semihosting: Move hw/semihosting/ -> semihosting/

With the exception of hw/core/, the hw/ directory only contains
device models used in system emulation. Semihosting is also used
by user emulation. As a generic feature, move it out of hw/ directory.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210226131356.3964782-3-f4bug@amsat.org>
Message-Id: <20210305135451.15427-3-alex.bennee@linaro.org>

6 files changed, 1726 insertions, 0 deletions

diff --git a/semihosting/Kconfig b/semihosting/Kconfig
new file mode 100644
index 0000000000..eaf3a20ef5
--- /dev/null
+++ b/semihosting/Kconfig
@@ -0,0 +1,7 @@
+
+config SEMIHOSTING
+       bool
+
+config ARM_COMPATIBLE_SEMIHOSTING
+       bool
+       select SEMIHOSTING
diff --git a/semihosting/arm-compat-semi.c b/semihosting/arm-compat-semi.c
new file mode 100644
index 0000000000..94950b6c56
--- /dev/null
+++ b/semihosting/arm-compat-semi.c
@@ -0,0 +1,1306 @@
+/*
+ *  Semihosting support for systems modeled on the Arm "Angel"
+ *  semihosting syscalls design. This includes Arm and RISC-V processors
+ *
+ *  Copyright (c) 2005, 2007 CodeSourcery.
+ *  Copyright (c) 2019 Linaro
+ *  Written by Paul Brook.
+ *
+ *  Copyright © 2020 by Keith Packard <keithp@keithp.com>
+ *  Adapted for systems other than ARM, including RISC-V, by Keith Packard
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ *  ARM Semihosting is documented in:
+ *     Semihosting for AArch32 and AArch64 Release 2.0
+ *     https://static.docs.arm.com/100863/0200/semihosting.pdf
+ *
+ *  RISC-V Semihosting is documented in:
+ *     RISC-V Semihosting
+ *     https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc
+ */
+
+#include "qemu/osdep.h"
+
+#include "cpu.h"
+#include "semihosting/semihost.h"
+#include "semihosting/console.h"
+#include "semihosting/common-semi.h"
+#include "qemu/log.h"
+#include "qemu/timer.h"
+#ifdef CONFIG_USER_ONLY
+#include "qemu.h"
+
+#define COMMON_SEMI_HEAP_SIZE (128 * 1024 * 1024)
+#else
+#include "exec/gdbstub.h"
+#include "qemu/cutils.h"
+#ifdef TARGET_ARM
+#include "hw/arm/boot.h"
+#endif
+#include "hw/boards.h"
+#endif
+
+#define TARGET_SYS_OPEN        0x01
+#define TARGET_SYS_CLOSE       0x02
+#define TARGET_SYS_WRITEC      0x03
+#define TARGET_SYS_WRITE0      0x04
+#define TARGET_SYS_WRITE       0x05
+#define TARGET_SYS_READ        0x06
+#define TARGET_SYS_READC       0x07
+#define TARGET_SYS_ISERROR     0x08
+#define TARGET_SYS_ISTTY       0x09
+#define TARGET_SYS_SEEK        0x0a
+#define TARGET_SYS_FLEN        0x0c
+#define TARGET_SYS_TMPNAM      0x0d
+#define TARGET_SYS_REMOVE      0x0e
+#define TARGET_SYS_RENAME      0x0f
+#define TARGET_SYS_CLOCK       0x10
+#define TARGET_SYS_TIME        0x11
+#define TARGET_SYS_SYSTEM      0x12
+#define TARGET_SYS_ERRNO       0x13
+#define TARGET_SYS_GET_CMDLINE 0x15
+#define TARGET_SYS_HEAPINFO    0x16
+#define TARGET_SYS_EXIT        0x18
+#define TARGET_SYS_SYNCCACHE   0x19
+#define TARGET_SYS_EXIT_EXTENDED 0x20
+#define TARGET_SYS_ELAPSED     0x30
+#define TARGET_SYS_TICKFREQ    0x31
+
+/* ADP_Stopped_ApplicationExit is used for exit(0),
+ * anything else is implemented as exit(1) */
+#define ADP_Stopped_ApplicationExit     (0x20026)
+
+#ifndef O_BINARY
+#define O_BINARY 0
+#endif
+
+#define GDB_O_RDONLY  0x000
+#define GDB_O_WRONLY  0x001
+#define GDB_O_RDWR    0x002
+#define GDB_O_APPEND  0x008
+#define GDB_O_CREAT   0x200
+#define GDB_O_TRUNC   0x400
+#define GDB_O_BINARY  0
+
+static int gdb_open_modeflags[12] = {
+    GDB_O_RDONLY,
+    GDB_O_RDONLY | GDB_O_BINARY,
+    GDB_O_RDWR,
+    GDB_O_RDWR | GDB_O_BINARY,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC | GDB_O_BINARY,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC | GDB_O_BINARY,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND | GDB_O_BINARY,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND | GDB_O_BINARY
+};
+
+static int open_modeflags[12] = {
+    O_RDONLY,
+    O_RDONLY | O_BINARY,
+    O_RDWR,
+    O_RDWR | O_BINARY,
+    O_WRONLY | O_CREAT | O_TRUNC,
+    O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
+    O_RDWR | O_CREAT | O_TRUNC,
+    O_RDWR | O_CREAT | O_TRUNC | O_BINARY,
+    O_WRONLY | O_CREAT | O_APPEND,
+    O_WRONLY | O_CREAT | O_APPEND | O_BINARY,
+    O_RDWR | O_CREAT | O_APPEND,
+    O_RDWR | O_CREAT | O_APPEND | O_BINARY
+};
+
+typedef enum GuestFDType {
+    GuestFDUnused = 0,
+    GuestFDHost = 1,
+    GuestFDGDB = 2,
+    GuestFDFeatureFile = 3,
+} GuestFDType;
+
+/*
+ * Guest file descriptors are integer indexes into an array of
+ * these structures (we will dynamically resize as necessary).
+ */
+typedef struct GuestFD {
+    GuestFDType type;
+    union {
+        int hostfd;
+        target_ulong featurefile_offset;
+    };
+} GuestFD;
+
+static GArray *guestfd_array;
+
+#ifndef CONFIG_USER_ONLY
+#include "exec/address-spaces.h"
+/*
+ * Find the base of a RAM region containing the specified address
+ */
+static inline hwaddr
+common_semi_find_region_base(hwaddr addr)
+{
+    MemoryRegion *subregion;
+
+    /*
+     * Find the chunk of R/W memory containing the address.  This is
+     * used for the SYS_HEAPINFO semihosting call, which should
+     * probably be using information from the loaded application.
+     */
+    QTAILQ_FOREACH(subregion, &get_system_memory()->subregions,
+                   subregions_link) {
+        if (subregion->ram && !subregion->readonly) {
+            Int128 top128 = int128_add(int128_make64(subregion->addr),
+                                       subregion->size);
+            Int128 addr128 = int128_make64(addr);
+            if (subregion->addr <= addr && int128_lt(addr128, top128)) {
+                return subregion->addr;
+            }
+        }
+    }
+    return 0;
+}
+#endif
+
+#ifdef TARGET_ARM
+static inline target_ulong
+common_semi_arg(CPUState *cs, int argno)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    if (is_a64(env)) {
+        return env->xregs[argno];
+    } else {
+        return env->regs[argno];
+    }
+}
+
+static inline void
+common_semi_set_ret(CPUState *cs, target_ulong ret)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    if (is_a64(env)) {
+        env->xregs[0] = ret;
+    } else {
+        env->regs[0] = ret;
+    }
+}
+
+static inline bool
+common_semi_sys_exit_extended(CPUState *cs, int nr)
+{
+    return (nr == TARGET_SYS_EXIT_EXTENDED || is_a64(cs->env_ptr));
+}
+
+#ifndef CONFIG_USER_ONLY
+#include "hw/arm/boot.h"
+static inline target_ulong
+common_semi_rambase(CPUState *cs)
+{
+    CPUArchState *env = cs->env_ptr;
+    const struct arm_boot_info *info = env->boot_info;
+    target_ulong sp;
+
+    if (info) {
+        return info->loader_start;
+    }
+
+    if (is_a64(env)) {
+        sp = env->xregs[31];
+    } else {
+        sp = env->regs[13];
+    }
+    return common_semi_find_region_base(sp);
+}
+#endif
+
+#endif /* TARGET_ARM */
+
+#ifdef TARGET_RISCV
+static inline target_ulong
+common_semi_arg(CPUState *cs, int argno)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+    return env->gpr[xA0 + argno];
+}
+
+static inline void
+common_semi_set_ret(CPUState *cs, target_ulong ret)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+    env->gpr[xA0] = ret;
+}
+
+static inline bool
+common_semi_sys_exit_extended(CPUState *cs, int nr)
+{
+    return (nr == TARGET_SYS_EXIT_EXTENDED || sizeof(target_ulong) == 8);
+}
+
+#ifndef CONFIG_USER_ONLY
+
+static inline target_ulong
+common_semi_rambase(CPUState *cs)
+{
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+    return common_semi_find_region_base(env->gpr[xSP]);
+}
+#endif
+
+#endif
+
+/*
+ * Allocate a new guest file descriptor and return it; if we
+ * couldn't allocate a new fd then return -1.
+ * This is a fairly simplistic implementation because we don't
+ * expect that most semihosting guest programs will make very
+ * heavy use of opening and closing fds.
+ */
+static int alloc_guestfd(void)
+{
+    guint i;
+
+    if (!guestfd_array) {
+        /* New entries zero-initialized, i.e. type GuestFDUnused */
+        guestfd_array = g_array_new(FALSE, TRUE, sizeof(GuestFD));
+    }
+
+    /* SYS_OPEN should return nonzero handle on success. Start guestfd from 1 */
+    for (i = 1; i < guestfd_array->len; i++) {
+        GuestFD *gf = &g_array_index(guestfd_array, GuestFD, i);
+
+        if (gf->type == GuestFDUnused) {
+            return i;
+        }
+    }
+
+    /* All elements already in use: expand the array */
+    g_array_set_size(guestfd_array, i + 1);
+    return i;
+}
+
+/*
+ * Look up the guestfd in the data structure; return NULL
+ * for out of bounds, but don't check whether the slot is unused.
+ * This is used internally by the other guestfd functions.
+ */
+static GuestFD *do_get_guestfd(int guestfd)
+{
+    if (!guestfd_array) {
+        return NULL;
+    }
+
+    if (guestfd <= 0 || guestfd >= guestfd_array->len) {
+        return NULL;
+    }
+
+    return &g_array_index(guestfd_array, GuestFD, guestfd);
+}
+
+/*
+ * Associate the specified guest fd (which must have been
+ * allocated via alloc_fd() and not previously used) with
+ * the specified host/gdb fd.
+ */
+static void associate_guestfd(int guestfd, int hostfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = use_gdb_syscalls() ? GuestFDGDB : GuestFDHost;
+    gf->hostfd = hostfd;
+}
+
+/*
+ * Deallocate the specified guest file descriptor. This doesn't
+ * close the host fd, it merely undoes the work of alloc_fd().
+ */
+static void dealloc_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = GuestFDUnused;
+}
+
+/*
+ * Given a guest file descriptor, get the associated struct.
+ * If the fd is not valid, return NULL. This is the function
+ * used by the various semihosting calls to validate a handle
+ * from the guest.
+ * Note: calling alloc_guestfd() or dealloc_guestfd() will
+ * invalidate any GuestFD* obtained by calling this function.
+ */
+static GuestFD *get_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    if (!gf || gf->type == GuestFDUnused) {
+        return NULL;
+    }
+    return gf;
+}
+
+/*
+ * The semihosting API has no concept of its errno being thread-safe,
+ * as the API design predates SMP CPUs and was intended as a simple
+ * real-hardware set of debug functionality. For QEMU, we make the
+ * errno be per-thread in linux-user mode; in softmmu it is a simple
+ * global, and we assume that the guest takes care of avoiding any races.
+ */
+#ifndef CONFIG_USER_ONLY
+static target_ulong syscall_err;
+
+#include "exec/softmmu-semi.h"
+#endif
+
+static inline uint32_t set_swi_errno(CPUState *cs, uint32_t code)
+{
+    if (code == (uint32_t)-1) {
+#ifdef CONFIG_USER_ONLY
+        TaskState *ts = cs->opaque;
+
+        ts->swi_errno = errno;
+#else
+        syscall_err = errno;
+#endif
+    }
+    return code;
+}
+
+static inline uint32_t get_swi_errno(CPUState *cs)
+{
+#ifdef CONFIG_USER_ONLY
+    TaskState *ts = cs->opaque;
+
+    return ts->swi_errno;
+#else
+    return syscall_err;
+#endif
+}
+
+static target_ulong common_semi_syscall_len;
+
+static void common_semi_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    target_ulong reg0 = common_semi_arg(cs, 0);
+
+    if (ret == (target_ulong)-1) {
+        errno = err;
+        set_swi_errno(cs, -1);
+        reg0 = ret;
+    } else {
+        /* Fixup syscalls that use nonstardard return conventions.  */
+        switch (reg0) {
+        case TARGET_SYS_WRITE:
+        case TARGET_SYS_READ:
+            reg0 = common_semi_syscall_len - ret;
+            break;
+        case TARGET_SYS_SEEK:
+            reg0 = 0;
+            break;
+        default:
+            reg0 = ret;
+            break;
+        }
+    }
+    common_semi_set_ret(cs, reg0);
+}
+
+static target_ulong common_semi_flen_buf(CPUState *cs)
+{
+    target_ulong sp;
+#ifdef TARGET_ARM
+    /* Return an address in target memory of 64 bytes where the remote
+     * gdb should write its stat struct. (The format of this structure
+     * is defined by GDB's remote protocol and is not target-specific.)
+     * We put this on the guest's stack just below SP.
+     */
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+
+    if (is_a64(env)) {
+        sp = env->xregs[31];
+    } else {
+        sp = env->regs[13];
+    }
+#endif
+#ifdef TARGET_RISCV
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    CPURISCVState *env = &cpu->env;
+
+    sp = env->gpr[xSP];
+#endif
+
+    return sp - 64;
+}
+
+static void
+common_semi_flen_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    /* The size is always stored in big-endian order, extract
+       the value. We assume the size always fit in 32 bits.  */
+    uint32_t size;
+    cpu_memory_rw_debug(cs, common_semi_flen_buf(cs) + 32,
+                        (uint8_t *)&size, 4, 0);
+    size = be32_to_cpu(size);
+    common_semi_set_ret(cs, size);
+    errno = err;
+    set_swi_errno(cs, -1);
+}
+
+static int common_semi_open_guestfd;
+
+static void
+common_semi_open_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    if (ret == (target_ulong)-1) {
+        errno = err;
+        set_swi_errno(cs, -1);
+        dealloc_guestfd(common_semi_open_guestfd);
+    } else {
+        associate_guestfd(common_semi_open_guestfd, ret);
+        ret = common_semi_open_guestfd;
+    }
+    common_semi_set_ret(cs, ret);
+}
+
+static target_ulong
+common_semi_gdb_syscall(CPUState *cs, gdb_syscall_complete_cb cb,
+                        const char *fmt, ...)
+{
+    va_list va;
+
+    va_start(va, fmt);
+    gdb_do_syscallv(cb, fmt, va);
+    va_end(va);
+
+    /*
+     * FIXME: in softmmu mode, the gdbstub will schedule our callback
+     * to occur, but will not actually call it to complete the syscall
+     * until after this function has returned and we are back in the
+     * CPU main loop. Therefore callers to this function must not
+     * do anything with its return value, because it is not necessarily
+     * the result of the syscall, but could just be the old value of X0.
+     * The only thing safe to do with this is that the callers of
+     * do_common_semihosting() will write it straight back into X0.
+     * (In linux-user mode, the callback will have happened before
+     * gdb_do_syscallv() returns.)
+     *
+     * We should tidy this up so neither this function nor
+     * do_common_semihosting() return a value, so the mistake of
+     * doing something with the return value is not possible to make.
+     */
+
+    return common_semi_arg(cs, 0);
+}
+
+/*
+ * Types for functions implementing various semihosting calls
+ * for specific types of guest file descriptor. These must all
+ * do the work and return the required return value for the guest,
+ * setting the guest errno if appropriate.
+ */
+typedef uint32_t sys_closefn(CPUState *cs, GuestFD *gf);
+typedef uint32_t sys_writefn(CPUState *cs, GuestFD *gf,
+                             target_ulong buf, uint32_t len);
+typedef uint32_t sys_readfn(CPUState *cs, GuestFD *gf,
+                            target_ulong buf, uint32_t len);
+typedef uint32_t sys_isattyfn(CPUState *cs, GuestFD *gf);
+typedef uint32_t sys_seekfn(CPUState *cs, GuestFD *gf,
+                            target_ulong offset);
+typedef uint32_t sys_flenfn(CPUState *cs, GuestFD *gf);
+
+static uint32_t host_closefn(CPUState *cs, GuestFD *gf)
+{
+    /*
+     * Only close the underlying host fd if it's one we opened on behalf
+     * of the guest in SYS_OPEN.
+     */
+    if (gf->hostfd == STDIN_FILENO ||
+        gf->hostfd == STDOUT_FILENO ||
+        gf->hostfd == STDERR_FILENO) {
+        return 0;
+    }
+    return set_swi_errno(cs, close(gf->hostfd));
+}
+
+static uint32_t host_writefn(CPUState *cs, GuestFD *gf,
+                             target_ulong buf, uint32_t len)
+{
+    CPUArchState *env = cs->env_ptr;
+    uint32_t ret;
+    char *s = lock_user(VERIFY_READ, buf, len, 1);
+    (void) env; /* Used in arm softmmu lock_user implicitly */
+    if (!s) {
+        /* Return bytes not written on error */
+        return len;
+    }
+    ret = set_swi_errno(cs, write(gf->hostfd, s, len));
+    unlock_user(s, buf, 0);
+    if (ret == (uint32_t)-1) {
+        ret = 0;
+    }
+    /* Return bytes not written */
+    return len - ret;
+}
+
+static uint32_t host_readfn(CPUState *cs, GuestFD *gf,
+                            target_ulong buf, uint32_t len)
+{
+    CPUArchState *env = cs->env_ptr;
+    uint32_t ret;
+    char *s = lock_user(VERIFY_WRITE, buf, len, 0);
+    (void) env; /* Used in arm softmmu lock_user implicitly */
+    if (!s) {
+        /* return bytes not read */
+        return len;
+    }
+    do {
+        ret = set_swi_errno(cs, read(gf->hostfd, s, len));
+    } while (ret == -1 && errno == EINTR);
+    unlock_user(s, buf, len);
+    if (ret == (uint32_t)-1) {
+        ret = 0;
+    }
+    /* Return bytes not read */
+    return len - ret;
+}
+
+static uint32_t host_isattyfn(CPUState *cs, GuestFD *gf)
+{
+    return isatty(gf->hostfd);
+}
+
+static uint32_t host_seekfn(CPUState *cs, GuestFD *gf, target_ulong offset)
+{
+    uint32_t ret = set_swi_errno(cs, lseek(gf->hostfd, offset, SEEK_SET));
+    if (ret == (uint32_t)-1) {
+        return -1;
+    }
+    return 0;
+}
+
+static uint32_t host_flenfn(CPUState *cs, GuestFD *gf)
+{
+    struct stat buf;
+    uint32_t ret = set_swi_errno(cs, fstat(gf->hostfd, &buf));
+    if (ret == (uint32_t)-1) {
+        return -1;
+    }
+    return buf.st_size;
+}
+
+static uint32_t gdb_closefn(CPUState *cs, GuestFD *gf)
+{
+    return common_semi_gdb_syscall(cs, common_semi_cb, "close,%x", gf->hostfd);
+}
+
+static uint32_t gdb_writefn(CPUState *cs, GuestFD *gf,
+                            target_ulong buf, uint32_t len)
+{
+    common_semi_syscall_len = len;
+    return common_semi_gdb_syscall(cs, common_semi_cb, "write,%x,%x,%x",
+                                   gf->hostfd, buf, len);
+}
+
+static uint32_t gdb_readfn(CPUState *cs, GuestFD *gf,
+                           target_ulong buf, uint32_t len)
+{
+    common_semi_syscall_len = len;
+    return common_semi_gdb_syscall(cs, common_semi_cb, "read,%x,%x,%x",
+                                   gf->hostfd, buf, len);
+}
+
+static uint32_t gdb_isattyfn(CPUState *cs, GuestFD *gf)
+{
+    return common_semi_gdb_syscall(cs, common_semi_cb, "isatty,%x", gf->hostfd);
+}
+
+static uint32_t gdb_seekfn(CPUState *cs, GuestFD *gf, target_ulong offset)
+{
+    return common_semi_gdb_syscall(cs, common_semi_cb, "lseek,%x,%x,0",
+                                   gf->hostfd, offset);
+}
+
+static uint32_t gdb_flenfn(CPUState *cs, GuestFD *gf)
+{
+    return common_semi_gdb_syscall(cs, common_semi_flen_cb, "fstat,%x,%x",
+                                   gf->hostfd, common_semi_flen_buf(cs));
+}
+
+#define SHFB_MAGIC_0 0x53
+#define SHFB_MAGIC_1 0x48
+#define SHFB_MAGIC_2 0x46
+#define SHFB_MAGIC_3 0x42
+
+/* Feature bits reportable in feature byte 0 */
+#define SH_EXT_EXIT_EXTENDED (1 << 0)
+#define SH_EXT_STDOUT_STDERR (1 << 1)
+
+static const uint8_t featurefile_data[] = {
+    SHFB_MAGIC_0,
+    SHFB_MAGIC_1,
+    SHFB_MAGIC_2,
+    SHFB_MAGIC_3,
+    SH_EXT_EXIT_EXTENDED | SH_EXT_STDOUT_STDERR, /* Feature byte 0 */
+};
+
+static void init_featurefile_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = GuestFDFeatureFile;
+    gf->featurefile_offset = 0;
+}
+
+static uint32_t featurefile_closefn(CPUState *cs, GuestFD *gf)
+{
+    /* Nothing to do */
+    return 0;
+}
+
+static uint32_t featurefile_writefn(CPUState *cs, GuestFD *gf,
+                                    target_ulong buf, uint32_t len)
+{
+    /* This fd can never be open for writing */
+
+    errno = EBADF;
+    return set_swi_errno(cs, -1);
+}
+
+static uint32_t featurefile_readfn(CPUState *cs, GuestFD *gf,
+                                   target_ulong buf, uint32_t len)
+{
+    CPUArchState *env = cs->env_ptr;
+    uint32_t i;
+    char *s;
+
+    (void) env; /* Used in arm softmmu lock_user implicitly */
+    s = lock_user(VERIFY_WRITE, buf, len, 0);
+    if (!s) {
+        return len;
+    }
+
+    for (i = 0; i < len; i++) {
+        if (gf->featurefile_offset >= sizeof(featurefile_data)) {
+            break;
+        }
+        s[i] = featurefile_data[gf->featurefile_offset];
+        gf->featurefile_offset++;
+    }
+
+    unlock_user(s, buf, len);
+
+    /* Return number of bytes not read */
+    return len - i;
+}
+
+static uint32_t featurefile_isattyfn(CPUState *cs, GuestFD *gf)
+{
+    return 0;
+}
+
+static uint32_t featurefile_seekfn(CPUState *cs, GuestFD *gf,
+                                   target_ulong offset)
+{
+    gf->featurefile_offset = offset;
+    return 0;
+}
+
+static uint32_t featurefile_flenfn(CPUState *cs, GuestFD *gf)
+{
+    return sizeof(featurefile_data);
+}
+
+typedef struct GuestFDFunctions {
+    sys_closefn *closefn;
+    sys_writefn *writefn;
+    sys_readfn *readfn;
+    sys_isattyfn *isattyfn;
+    sys_seekfn *seekfn;
+    sys_flenfn *flenfn;
+} GuestFDFunctions;
+
+static const GuestFDFunctions guestfd_fns[] = {
+    [GuestFDHost] = {
+        .closefn = host_closefn,
+        .writefn = host_writefn,
+        .readfn = host_readfn,
+        .isattyfn = host_isattyfn,
+        .seekfn = host_seekfn,
+        .flenfn = host_flenfn,
+    },
+    [GuestFDGDB] = {
+        .closefn = gdb_closefn,
+        .writefn = gdb_writefn,
+        .readfn = gdb_readfn,
+        .isattyfn = gdb_isattyfn,
+        .seekfn = gdb_seekfn,
+        .flenfn = gdb_flenfn,
+    },
+    [GuestFDFeatureFile] = {
+        .closefn = featurefile_closefn,
+        .writefn = featurefile_writefn,
+        .readfn = featurefile_readfn,
+        .isattyfn = featurefile_isattyfn,
+        .seekfn = featurefile_seekfn,
+        .flenfn = featurefile_flenfn,
+    },
+};
+
+/* Read the input value from the argument block; fail the semihosting
+ * call if the memory read fails.
+ */
+#ifdef TARGET_ARM
+#define GET_ARG(n) do {                                 \
+    if (is_a64(env)) {                                  \
+        if (get_user_u64(arg ## n, args + (n) * 8)) {   \
+            errno = EFAULT;                             \
+            return set_swi_errno(cs, -1);              \
+        }                                               \
+    } else {                                            \
+        if (get_user_u32(arg ## n, args + (n) * 4)) {   \
+            errno = EFAULT;                             \
+            return set_swi_errno(cs, -1);              \
+        }                                               \
+    }                                                   \
+} while (0)
+
+#define SET_ARG(n, val)                                 \
+    (is_a64(env) ?                                      \
+     put_user_u64(val, args + (n) * 8) :                \
+     put_user_u32(val, args + (n) * 4))
+#endif
+
+#ifdef TARGET_RISCV
+
+/*
+ * get_user_ual is defined as get_user_u32 in softmmu-semi.h,
+ * we need a macro that fetches a target_ulong
+ */
+#define get_user_utl(arg, p)                    \
+    ((sizeof(target_ulong) == 8) ?              \
+     get_user_u64(arg, p) :                     \
+     get_user_u32(arg, p))
+
+/*
+ * put_user_ual is defined as put_user_u32 in softmmu-semi.h,
+ * we need a macro that stores a target_ulong
+ */
+#define put_user_utl(arg, p)                    \
+    ((sizeof(target_ulong) == 8) ?              \
+     put_user_u64(arg, p) :                     \
+     put_user_u32(arg, p))
+
+#define GET_ARG(n) do {                                                 \
+        if (get_user_utl(arg ## n, args + (n) * sizeof(target_ulong))) { \
+            errno = EFAULT;                                             \
+            return set_swi_errno(cs, -1);                              \
+        }                                                               \
+    } while (0)
+
+#define SET_ARG(n, val)                                 \
+    put_user_utl(val, args + (n) * sizeof(target_ulong))
+#endif
+
+/*
+ * Do a semihosting call.
+ *
+ * The specification always says that the "return register" either
+ * returns a specific value or is corrupted, so we don't need to
+ * report to our caller whether we are returning a value or trying to
+ * leave the register unchanged. We use 0xdeadbeef as the return value
+ * when there isn't a defined return value for the call.
+ */
+target_ulong do_common_semihosting(CPUState *cs)
+{
+    CPUArchState *env = cs->env_ptr;
+    target_ulong args;
+    target_ulong arg0, arg1, arg2, arg3;
+    target_ulong ul_ret;
+    char * s;
+    int nr;
+    uint32_t ret;
+    uint32_t len;
+    GuestFD *gf;
+    int64_t elapsed;
+
+    (void) env; /* Used implicitly by arm lock_user macro */
+    nr = common_semi_arg(cs, 0) & 0xffffffffU;
+    args = common_semi_arg(cs, 1);
+
+    switch (nr) {
+    case TARGET_SYS_OPEN:
+    {
+        int guestfd;
+
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        s = lock_user_string(arg0);
+        if (!s) {
+            errno = EFAULT;
+            return set_swi_errno(cs, -1);
+        }
+        if (arg1 >= 12) {
+            unlock_user(s, arg0, 0);
+            errno = EINVAL;
+            return set_swi_errno(cs, -1);
+        }
+
+        guestfd = alloc_guestfd();
+        if (guestfd < 0) {
+            unlock_user(s, arg0, 0);
+            errno = EMFILE;
+            return set_swi_errno(cs, -1);
+        }
+
+        if (strcmp(s, ":tt") == 0) {
+            int result_fileno;
+
+            /*
+             * We implement SH_EXT_STDOUT_STDERR, so:
+             *  open for read == stdin
+             *  open for write == stdout
+             *  open for append == stderr
+             */
+            if (arg1 < 4) {
+                result_fileno = STDIN_FILENO;
+            } else if (arg1 < 8) {
+                result_fileno = STDOUT_FILENO;
+            } else {
+                result_fileno = STDERR_FILENO;
+            }
+            associate_guestfd(guestfd, result_fileno);
+            unlock_user(s, arg0, 0);
+            return guestfd;
+        }
+        if (strcmp(s, ":semihosting-features") == 0) {
+            unlock_user(s, arg0, 0);
+            /* We must fail opens for modes other than 0 ('r') or 1 ('rb') */
+            if (arg1 != 0 && arg1 != 1) {
+                dealloc_guestfd(guestfd);
+                errno = EACCES;
+                return set_swi_errno(cs, -1);
+            }
+            init_featurefile_guestfd(guestfd);
+            return guestfd;
+        }
+
+        if (use_gdb_syscalls()) {
+            common_semi_open_guestfd = guestfd;
+            ret = common_semi_gdb_syscall(cs, common_semi_open_cb,
+                                          "open,%s,%x,1a4", arg0, (int)arg2 + 1,
+                                          gdb_open_modeflags[arg1]);
+        } else {
+            ret = set_swi_errno(cs, open(s, open_modeflags[arg1], 0644));
+            if (ret == (uint32_t)-1) {
+                dealloc_guestfd(guestfd);
+            } else {
+                associate_guestfd(guestfd, ret);
+                ret = guestfd;
+            }
+        }
+        unlock_user(s, arg0, 0);
+        return ret;
+    }
+    case TARGET_SYS_CLOSE:
+        GET_ARG(0);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(cs, -1);
+        }
+
+        ret = guestfd_fns[gf->type].closefn(cs, gf);
+        dealloc_guestfd(arg0);
+        return ret;
+    case TARGET_SYS_WRITEC:
+        qemu_semihosting_console_outc(cs->env_ptr, args);
+        return 0xdeadbeef;
+    case TARGET_SYS_WRITE0:
+        return qemu_semihosting_console_outs(cs->env_ptr, args);
+    case TARGET_SYS_WRITE:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        len = arg2;
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(cs, -1);
+        }
+
+        return guestfd_fns[gf->type].writefn(cs, gf, arg1, len);
+    case TARGET_SYS_READ:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        len = arg2;
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(cs, -1);
+        }
+
+        return guestfd_fns[gf->type].readfn(cs, gf, arg1, len);
+    case TARGET_SYS_READC:
+        return qemu_semihosting_console_inc(cs->env_ptr);
+    case TARGET_SYS_ISERROR:
+        GET_ARG(0);
+        return (target_long) arg0 < 0 ? 1 : 0;
+    case TARGET_SYS_ISTTY:
+        GET_ARG(0);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(cs, -1);
+        }
+
+        return guestfd_fns[gf->type].isattyfn(cs, gf);
+    case TARGET_SYS_SEEK:
+        GET_ARG(0);
+        GET_ARG(1);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(cs, -1);
+        }
+
+        return guestfd_fns[gf->type].seekfn(cs, gf, arg1);
+    case TARGET_SYS_FLEN:
+        GET_ARG(0);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(cs, -1);
+        }
+
+        return guestfd_fns[gf->type].flenfn(cs, gf);
+    case TARGET_SYS_TMPNAM:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        if (asprintf(&s, "/tmp/qemu-%x%02x", getpid(),
+                     (int) (arg1 & 0xff)) < 0) {
+            return -1;
+        }
+        ul_ret = (target_ulong) -1;
+
+        /* Make sure there's enough space in the buffer */
+        if (strlen(s) < arg2) {
+            char *output = lock_user(VERIFY_WRITE, arg0, arg2, 0);
+            strcpy(output, s);
+            unlock_user(output, arg0, arg2);
+            ul_ret = 0;
+        }
+        free(s);
+        return ul_ret;
+    case TARGET_SYS_REMOVE:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            ret = common_semi_gdb_syscall(cs, common_semi_cb, "unlink,%s",
+                                          arg0, (int)arg1 + 1);
+        } else {
+            s = lock_user_string(arg0);
+            if (!s) {
+                errno = EFAULT;
+                return set_swi_errno(cs, -1);
+            }
+            ret =  set_swi_errno(cs, remove(s));
+            unlock_user(s, arg0, 0);
+        }
+        return ret;
+    case TARGET_SYS_RENAME:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        GET_ARG(3);
+        if (use_gdb_syscalls()) {
+            return common_semi_gdb_syscall(cs, common_semi_cb, "rename,%s,%s",
+                                           arg0, (int)arg1 + 1, arg2,
+                                           (int)arg3 + 1);
+        } else {
+            char *s2;
+            s = lock_user_string(arg0);
+            s2 = lock_user_string(arg2);
+            if (!s || !s2) {
+                errno = EFAULT;
+                ret = set_swi_errno(cs, -1);
+            } else {
+                ret = set_swi_errno(cs, rename(s, s2));
+            }
+            if (s2)
+                unlock_user(s2, arg2, 0);
+            if (s)
+                unlock_user(s, arg0, 0);
+            return ret;
+        }
+    case TARGET_SYS_CLOCK:
+        return clock() / (CLOCKS_PER_SEC / 100);
+    case TARGET_SYS_TIME:
+        return set_swi_errno(cs, time(NULL));
+    case TARGET_SYS_SYSTEM:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            return common_semi_gdb_syscall(cs, common_semi_cb, "system,%s",
+                                           arg0, (int)arg1 + 1);
+        } else {
+            s = lock_user_string(arg0);
+            if (!s) {
+                errno = EFAULT;
+                return set_swi_errno(cs, -1);
+            }
+            ret = set_swi_errno(cs, system(s));
+            unlock_user(s, arg0, 0);
+            return ret;
+        }
+    case TARGET_SYS_ERRNO:
+        return get_swi_errno(cs);
+    case TARGET_SYS_GET_CMDLINE:
+        {
+            /* Build a command-line from the original argv.
+             *
+             * The inputs are:
+             *     * arg0, pointer to a buffer of at least the size
+             *               specified in arg1.
+             *     * arg1, size of the buffer pointed to by arg0 in
+             *               bytes.
+             *
+             * The outputs are:
+             *     * arg0, pointer to null-terminated string of the
+             *               command line.
+             *     * arg1, length of the string pointed to by arg0.
+             */
+
+            char *output_buffer;
+            size_t input_size;
+            size_t output_size;
+            int status = 0;
+#if !defined(CONFIG_USER_ONLY)
+            const char *cmdline;
+#else
+            TaskState *ts = cs->opaque;
+#endif
+            GET_ARG(0);
+            GET_ARG(1);
+            input_size = arg1;
+            /* Compute the size of the output string.  */
+#if !defined(CONFIG_USER_ONLY)
+            cmdline = semihosting_get_cmdline();
+            if (cmdline == NULL) {
+                cmdline = ""; /* Default to an empty line. */
+            }
+            output_size = strlen(cmdline) + 1; /* Count terminating 0. */
+#else
+            unsigned int i;
+
+            output_size = ts->info->arg_end - ts->info->arg_start;
+            if (!output_size) {
+                /*
+                 * We special-case the "empty command line" case (argc==0).
+                 * Just provide the terminating 0.
+                 */
+                output_size = 1;
+            }
+#endif
+
+            if (output_size > input_size) {
+                /* Not enough space to store command-line arguments.  */
+                errno = E2BIG;
+                return set_swi_errno(cs, -1);
+            }
+
+            /* Adjust the command-line length.  */
+            if (SET_ARG(1, output_size - 1)) {
+                /* Couldn't write back to argument block */
+                errno = EFAULT;
+                return set_swi_errno(cs, -1);
+            }
+
+            /* Lock the buffer on the ARM side.  */
+            output_buffer = lock_user(VERIFY_WRITE, arg0, output_size, 0);
+            if (!output_buffer) {
+                errno = EFAULT;
+                return set_swi_errno(cs, -1);
+            }
+
+            /* Copy the command-line arguments.  */
+#if !defined(CONFIG_USER_ONLY)
+            pstrcpy(output_buffer, output_size, cmdline);
+#else
+            if (output_size == 1) {
+                /* Empty command-line.  */
+                output_buffer[0] = '\0';
+                goto out;
+            }
+
+            if (copy_from_user(output_buffer, ts->info->arg_start,
+                               output_size)) {
+                errno = EFAULT;
+                status = set_swi_errno(cs, -1);
+                goto out;
+            }
+
+            /* Separate arguments by white spaces.  */
+            for (i = 0; i < output_size - 1; i++) {
+                if (output_buffer[i] == 0) {
+                    output_buffer[i] = ' ';
+                }
+            }
+        out:
+#endif
+            /* Unlock the buffer on the ARM side.  */
+            unlock_user(output_buffer, arg0, output_size);
+
+            return status;
+        }
+    case TARGET_SYS_HEAPINFO:
+        {
+            target_ulong retvals[4];
+            target_ulong limit;
+            int i;
+#ifdef CONFIG_USER_ONLY
+            TaskState *ts = cs->opaque;
+#else
+            target_ulong rambase = common_semi_rambase(cs);
+#endif
+
+            GET_ARG(0);
+
+#ifdef CONFIG_USER_ONLY
+            /*
+             * Some C libraries assume the heap immediately follows .bss, so
+             * allocate it using sbrk.
+             */
+            if (!ts->heap_limit) {
+                abi_ulong ret;
+
+                ts->heap_base = do_brk(0);
+                limit = ts->heap_base + COMMON_SEMI_HEAP_SIZE;
+                /* Try a big heap, and reduce the size if that fails.  */
+                for (;;) {
+                    ret = do_brk(limit);
+                    if (ret >= limit) {
+                        break;
+                    }
+                    limit = (ts->heap_base >> 1) + (limit >> 1);
+                }
+                ts->heap_limit = limit;
+            }
+
+            retvals[0] = ts->heap_base;
+            retvals[1] = ts->heap_limit;
+            retvals[2] = ts->stack_base;
+            retvals[3] = 0; /* Stack limit.  */
+#else
+            limit = current_machine->ram_size;
+            /* TODO: Make this use the limit of the loaded application.  */
+            retvals[0] = rambase + limit / 2;
+            retvals[1] = rambase + limit;
+            retvals[2] = rambase + limit; /* Stack base */
+            retvals[3] = rambase; /* Stack limit.  */
+#endif
+
+            for (i = 0; i < ARRAY_SIZE(retvals); i++) {
+                bool fail;
+
+                fail = SET_ARG(i, retvals[i]);
+
+                if (fail) {
+                    /* Couldn't write back to argument block */
+                    errno = EFAULT;
+                    return set_swi_errno(cs, -1);
+                }
+            }
+            return 0;
+        }
+    case TARGET_SYS_EXIT:
+    case TARGET_SYS_EXIT_EXTENDED:
+        if (common_semi_sys_exit_extended(cs, nr)) {
+            /*
+             * The A64 version of SYS_EXIT takes a parameter block,
+             * so the application-exit type can return a subcode which
+             * is the exit status code from the application.
+             * SYS_EXIT_EXTENDED is an a new-in-v2.0 optional function
+             * which allows A32/T32 guests to also provide a status code.
+             */
+            GET_ARG(0);
+            GET_ARG(1);
+
+            if (arg0 == ADP_Stopped_ApplicationExit) {
+                ret = arg1;
+            } else {
+                ret = 1;
+            }
+        } else {
+            /*
+             * The A32/T32 version of SYS_EXIT specifies only
+             * Stopped_ApplicationExit as normal exit, but does not
+             * allow the guest to specify the exit status code.
+             * Everything else is considered an error.
+             */
+            ret = (args == ADP_Stopped_ApplicationExit) ? 0 : 1;
+        }
+        gdb_exit(ret);
+        exit(ret);
+    case TARGET_SYS_ELAPSED:
+        elapsed = get_clock() - clock_start;
+        if (sizeof(target_ulong) == 8) {
+            SET_ARG(0, elapsed);
+        } else {
+            SET_ARG(0, (uint32_t) elapsed);
+            SET_ARG(1, (uint32_t) (elapsed >> 32));
+        }
+        return 0;
+    case TARGET_SYS_TICKFREQ:
+        /* qemu always uses nsec */
+        return 1000000000;
+    case TARGET_SYS_SYNCCACHE:
+        /*
+         * Clean the D-cache and invalidate the I-cache for the specified
+         * virtual address range. This is a nop for us since we don't
+         * implement caches. This is only present on A64.
+         */
+#ifdef TARGET_ARM
+        if (is_a64(cs->env_ptr)) {
+            return 0;
+        }
+#endif
+#ifdef TARGET_RISCV
+        return 0;
+#endif
+        /* fall through -- invalid for A32/T32 */
+    default:
+        fprintf(stderr, "qemu: Unsupported SemiHosting SWI 0x%02x\n", nr);
+        cpu_dump_state(cs, stderr, 0);
+        abort();
+    }
+}
diff --git a/semihosting/common-semi.h b/semihosting/common-semi.h
new file mode 100644
index 0000000000..0bfab1c669
--- /dev/null
+++ b/semihosting/common-semi.h
@@ -0,0 +1,39 @@
+/*
+ *  Semihosting support for systems modeled on the Arm "Angel"
+ *  semihosting syscalls design. This includes Arm and RISC-V processors
+ *
+ *  Copyright (c) 2005, 2007 CodeSourcery.
+ *  Copyright (c) 2019 Linaro
+ *  Written by Paul Brook.
+ *
+ *  Copyright © 2020 by Keith Packard <keithp@keithp.com>
+ *  Adapted for systems other than ARM, including RISC-V, by Keith Packard
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ *  ARM Semihosting is documented in:
+ *     Semihosting for AArch32 and AArch64 Release 2.0
+ *     https://static.docs.arm.com/100863/0200/semihosting.pdf
+ *
+ *  RISC-V Semihosting is documented in:
+ *     RISC-V Semihosting
+ *     https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc
+ */
+
+#ifndef COMMON_SEMI_H
+#define COMMON_SEMI_H
+
+target_ulong do_common_semihosting(CPUState *cs);
+
+#endif /* COMMON_SEMI_H */
diff --git a/semihosting/config.c b/semihosting/config.c
new file mode 100644
index 0000000000..3548e0f627
--- /dev/null
+++ b/semihosting/config.c
@@ -0,0 +1,187 @@
+/*
+ * Semihosting configuration
+ *
+ * Copyright (c) 2015 Imagination Technologies
+ * Copyright (c) 2019 Linaro Ltd
+ *
+ * This controls the configuration of semihosting for all guest
+ * targets that support it. Architecture specific handling is handled
+ * in target/HW/HW-semi.c
+ *
+ * Semihosting is sightly strange in that it is also supported by some
+ * linux-user targets. However in that use case no configuration of
+ * the outputs and command lines is supported.
+ *
+ * The config module is common to all softmmu targets however as vl.c
+ * needs to link against the helpers.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/option.h"
+#include "qemu/config-file.h"
+#include "qemu/error-report.h"
+#include "semihosting/semihost.h"
+#include "chardev/char.h"
+#include "sysemu/sysemu.h"
+
+QemuOptsList qemu_semihosting_config_opts = {
+    .name = "semihosting-config",
+    .implied_opt_name = "enable",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_semihosting_config_opts.head),
+    .desc = {
+        {
+            .name = "enable",
+            .type = QEMU_OPT_BOOL,
+        }, {
+            .name = "target",
+            .type = QEMU_OPT_STRING,
+        }, {
+            .name = "chardev",
+            .type = QEMU_OPT_STRING,
+        }, {
+            .name = "arg",
+            .type = QEMU_OPT_STRING,
+        },
+        { /* end of list */ }
+    },
+};
+
+typedef struct SemihostingConfig {
+    bool enabled;
+    SemihostingTarget target;
+    Chardev *chardev;
+    const char **argv;
+    int argc;
+    const char *cmdline; /* concatenated argv */
+} SemihostingConfig;
+
+static SemihostingConfig semihosting;
+static const char *semihost_chardev;
+
+bool semihosting_enabled(void)
+{
+    return semihosting.enabled;
+}
+
+SemihostingTarget semihosting_get_target(void)
+{
+    return semihosting.target;
+}
+
+const char *semihosting_get_arg(int i)
+{
+    if (i >= semihosting.argc) {
+        return NULL;
+    }
+    return semihosting.argv[i];
+}
+
+int semihosting_get_argc(void)
+{
+    return semihosting.argc;
+}
+
+const char *semihosting_get_cmdline(void)
+{
+    if (semihosting.cmdline == NULL && semihosting.argc > 0) {
+        semihosting.cmdline = g_strjoinv(" ", (gchar **)semihosting.argv);
+    }
+    return semihosting.cmdline;
+}
+
+static int add_semihosting_arg(void *opaque,
+                               const char *name, const char *val,
+                               Error **errp)
+{
+    SemihostingConfig *s = opaque;
+    if (strcmp(name, "arg") == 0) {
+        s->argc++;
+        /* one extra element as g_strjoinv() expects NULL-terminated array */
+        s->argv = g_realloc(s->argv, (s->argc + 1) * sizeof(void *));
+        s->argv[s->argc - 1] = val;
+        s->argv[s->argc] = NULL;
+    }
+    return 0;
+}
+
+/* Use strings passed via -kernel/-append to initialize semihosting.argv[] */
+void semihosting_arg_fallback(const char *file, const char *cmd)
+{
+    char *cmd_token;
+
+    /* argv[0] */
+    add_semihosting_arg(&semihosting, "arg", file, NULL);
+
+    /* split -append and initialize argv[1..n] */
+    cmd_token = strtok(g_strdup(cmd), " ");
+    while (cmd_token) {
+        add_semihosting_arg(&semihosting, "arg", cmd_token, NULL);
+        cmd_token = strtok(NULL, " ");
+    }
+}
+
+Chardev *semihosting_get_chardev(void)
+{
+    return semihosting.chardev;
+}
+
+void qemu_semihosting_enable(void)
+{
+    semihosting.enabled = true;
+    semihosting.target = SEMIHOSTING_TARGET_AUTO;
+}
+
+int qemu_semihosting_config_options(const char *optarg)
+{
+    QemuOptsList *opt_list = qemu_find_opts("semihosting-config");
+    QemuOpts *opts = qemu_opts_parse_noisily(opt_list, optarg, false);
+
+    semihosting.enabled = true;
+
+    if (opts != NULL) {
+        semihosting.enabled = qemu_opt_get_bool(opts, "enable",
+                                                true);
+        const char *target = qemu_opt_get(opts, "target");
+        /* setup of chardev is deferred until they are initialised */
+        semihost_chardev = qemu_opt_get(opts, "chardev");
+        if (target != NULL) {
+            if (strcmp("native", target) == 0) {
+                semihosting.target = SEMIHOSTING_TARGET_NATIVE;
+            } else if (strcmp("gdb", target) == 0) {
+                semihosting.target = SEMIHOSTING_TARGET_GDB;
+            } else  if (strcmp("auto", target) == 0) {
+                semihosting.target = SEMIHOSTING_TARGET_AUTO;
+            } else {
+                error_report("unsupported semihosting-config %s",
+                             optarg);
+                return 1;
+            }
+        } else {
+            semihosting.target = SEMIHOSTING_TARGET_AUTO;
+        }
+        /* Set semihosting argument count and vector */
+        qemu_opt_foreach(opts, add_semihosting_arg,
+                         &semihosting, NULL);
+    } else {
+        error_report("unsupported semihosting-config %s", optarg);
+        return 1;
+    }
+
+    return 0;
+}
+
+void qemu_semihosting_connect_chardevs(void)
+{
+    /* We had to defer this until chardevs were created */
+    if (semihost_chardev) {
+        Chardev *chr = qemu_chr_find(semihost_chardev);
+        if (chr == NULL) {
+            error_report("semihosting chardev '%s' not found",
+                         semihost_chardev);
+            exit(1);
+        }
+        semihosting.chardev = chr;
+    }
+}
diff --git a/semihosting/console.c b/semihosting/console.c
new file mode 100644
index 0000000000..c9ebd6fdd0
--- /dev/null
+++ b/semihosting/console.c
@@ -0,0 +1,180 @@
+/*
+ * Semihosting Console Support
+ *
+ * Copyright (c) 2015 Imagination Technologies
+ * Copyright (c) 2019 Linaro Ltd
+ *
+ * This provides support for outputting to a semihosting console.
+ *
+ * While most semihosting implementations support reading and writing
+ * to arbitrary file descriptors we treat the console as something
+ * specifically for debugging interaction. This means messages can be
+ * re-directed to gdb (if currently being used to debug) or even
+ * re-directed elsewhere.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "cpu.h"
+#include "semihosting/semihost.h"
+#include "semihosting/console.h"
+#include "exec/gdbstub.h"
+#include "exec/exec-all.h"
+#include "qemu/log.h"
+#include "chardev/char.h"
+#include "chardev/char-fe.h"
+#include "sysemu/sysemu.h"
+#include "qemu/main-loop.h"
+#include "qapi/error.h"
+#include "qemu/fifo8.h"
+
+int qemu_semihosting_log_out(const char *s, int len)
+{
+    Chardev *chardev = semihosting_get_chardev();
+    if (chardev) {
+        return qemu_chr_write_all(chardev, (uint8_t *) s, len);
+    } else {
+        return write(STDERR_FILENO, s, len);
+    }
+}
+
+/*
+ * A re-implementation of lock_user_string that we can use locally
+ * instead of relying on softmmu-semi. Hopefully we can deprecate that
+ * in time. Copy string until we find a 0 or address error.
+ */
+static GString *copy_user_string(CPUArchState *env, target_ulong addr)
+{
+    CPUState *cpu = env_cpu(env);
+    GString *s = g_string_sized_new(128);
+    uint8_t c;
+
+    do {
+        if (cpu_memory_rw_debug(cpu, addr++, &c, 1, 0) == 0) {
+            if (c) {
+                s = g_string_append_c(s, c);
+            }
+        } else {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "%s: passed inaccessible address " TARGET_FMT_lx,
+                          __func__, addr);
+            break;
+        }
+    } while (c!=0);
+
+    return s;
+}
+
+static void semihosting_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    if (ret == (target_ulong) -1) {
+        qemu_log("%s: gdb console output failed ("TARGET_FMT_ld")",
+                 __func__, err);
+    }
+}
+
+int qemu_semihosting_console_outs(CPUArchState *env, target_ulong addr)
+{
+    GString *s = copy_user_string(env, addr);
+    int out = s->len;
+
+    if (use_gdb_syscalls()) {
+        gdb_do_syscall(semihosting_cb, "write,2,%x,%x", addr, s->len);
+    } else {
+        out = qemu_semihosting_log_out(s->str, s->len);
+    }
+
+    g_string_free(s, true);
+    return out;
+}
+
+void qemu_semihosting_console_outc(CPUArchState *env, target_ulong addr)
+{
+    CPUState *cpu = env_cpu(env);
+    uint8_t c;
+
+    if (cpu_memory_rw_debug(cpu, addr, &c, 1, 0) == 0) {
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(semihosting_cb, "write,2,%x,%x", addr, 1);
+        } else {
+            qemu_semihosting_log_out((const char *) &c, 1);
+        }
+    } else {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: passed inaccessible address " TARGET_FMT_lx,
+                      __func__, addr);
+    }
+}
+
+#define FIFO_SIZE   1024
+
+/* Access to this structure is protected by the BQL */
+typedef struct SemihostingConsole {
+    CharBackend         backend;
+    GSList              *sleeping_cpus;
+    bool                got;
+    Fifo8               fifo;
+} SemihostingConsole;
+
+static SemihostingConsole console;
+
+static int console_can_read(void *opaque)
+{
+    SemihostingConsole *c = opaque;
+    int ret;
+    g_assert(qemu_mutex_iothread_locked());
+    ret = (int) fifo8_num_free(&c->fifo);
+    return ret;
+}
+
+static void console_wake_up(gpointer data, gpointer user_data)
+{
+    CPUState *cs = (CPUState *) data;
+    /* cpu_handle_halt won't know we have work so just unbung here */
+    cs->halted = 0;
+    qemu_cpu_kick(cs);
+}
+
+static void console_read(void *opaque, const uint8_t *buf, int size)
+{
+    SemihostingConsole *c = opaque;
+    g_assert(qemu_mutex_iothread_locked());
+    while (size-- && !fifo8_is_full(&c->fifo)) {
+        fifo8_push(&c->fifo, *buf++);
+    }
+    g_slist_foreach(c->sleeping_cpus, console_wake_up, NULL);
+    c->sleeping_cpus = NULL;
+}
+
+target_ulong qemu_semihosting_console_inc(CPUArchState *env)
+{
+    uint8_t ch;
+    SemihostingConsole *c = &console;
+    g_assert(qemu_mutex_iothread_locked());
+    g_assert(current_cpu);
+    if (fifo8_is_empty(&c->fifo)) {
+        c->sleeping_cpus = g_slist_prepend(c->sleeping_cpus, current_cpu);
+        current_cpu->halted = 1;
+        current_cpu->exception_index = EXCP_HALTED;
+        cpu_loop_exit(current_cpu);
+        /* never returns */
+    }
+    ch = fifo8_pop(&c->fifo);
+    return (target_ulong) ch;
+}
+
+void qemu_semihosting_console_init(void)
+{
+    Chardev *chr = semihosting_get_chardev();
+
+    if  (chr) {
+        fifo8_create(&console.fifo, FIFO_SIZE);
+        qemu_chr_fe_init(&console.backend, chr, &error_abort);
+        qemu_chr_fe_set_handlers(&console.backend,
+                                 console_can_read,
+                                 console_read,
+                                 NULL, NULL, &console,
+                                 NULL, true);
+    }
+}
diff --git a/semihosting/meson.build b/semihosting/meson.build
new file mode 100644
index 0000000000..ea8090abe3
--- /dev/null
+++ b/semihosting/meson.build
@@ -0,0 +1,7 @@
+specific_ss.add(when: 'CONFIG_SEMIHOSTING', if_true: files(
+  'config.c',
+  'console.c',
+))
+
+specific_ss.add(when: ['CONFIG_ARM_COMPATIBLE_SEMIHOSTING'],
+		if_true: files('arm-compat-semi.c'))