diff options
Diffstat (limited to 'common-user/host/arm/safe-syscall.inc.S')
| -rw-r--r-- | common-user/host/arm/safe-syscall.inc.S | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/common-user/host/arm/safe-syscall.inc.S b/common-user/host/arm/safe-syscall.inc.S new file mode 100644 index 0000000000..bbfb89634e --- /dev/null +++ b/common-user/host/arm/safe-syscall.inc.S @@ -0,0 +1,108 @@ +/* + * safe-syscall.inc.S : host-specific assembly fragment + * to handle signals occurring at the same time as system calls. + * This is intended to be included by common-user/safe-syscall.S + * + * Written by Richard Henderson <rth@twiddle.net> + * Copyright (C) 2016 Red Hat, Inc. + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ + + .global safe_syscall_base + .global safe_syscall_start + .global safe_syscall_end + .type safe_syscall_base, %function + + .cfi_sections .debug_frame + + .text + .syntax unified + .arm + .align 2 + + /* This is the entry point for making a system call. The calling + * convention here is that of a C varargs function with the + * first argument an 'int *' to the signal_pending flag, the + * second one the system call number (as a 'long'), and all further + * arguments being syscall arguments (also 'long'). + */ +safe_syscall_base: + .fnstart + .cfi_startproc + mov r12, sp /* save entry stack */ + push { r4, r5, r6, r7, r8, lr } + .save { r4, r5, r6, r7, r8, lr } + .cfi_adjust_cfa_offset 24 + .cfi_rel_offset r4, 0 + .cfi_rel_offset r5, 4 + .cfi_rel_offset r6, 8 + .cfi_rel_offset r7, 12 + .cfi_rel_offset r8, 16 + .cfi_rel_offset lr, 20 + + /* The syscall calling convention isn't the same as the C one: + * we enter with r0 == &signal_pending + * r1 == syscall number + * r2, r3, [sp+0] ... [sp+12] == syscall arguments + * and return the result in r0 + * and the syscall instruction needs + * r7 == syscall number + * r0 ... r6 == syscall arguments + * and returns the result in r0 + * Shuffle everything around appropriately. + * Note the 16 bytes that we pushed to save registers. + */ + mov r8, r0 /* copy signal_pending */ + mov r7, r1 /* syscall number */ + mov r0, r2 /* syscall args */ + mov r1, r3 + ldm r12, { r2, r3, r4, r5, r6 } + + /* This next sequence of code works in conjunction with the + * rewind_if_safe_syscall_function(). If a signal is taken + * and the interrupted PC is anywhere between 'safe_syscall_start' + * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. + * The code sequence must therefore be able to cope with this, and + * the syscall instruction must be the final one in the sequence. + */ +safe_syscall_start: + /* if signal_pending is non-zero, don't do the call */ + ldr r12, [r8] /* signal_pending */ + tst r12, r12 + bne 2f + swi 0 +safe_syscall_end: + + /* code path for having successfully executed the syscall */ +#if defined(__linux__) + /* Linux kernel returns (small) negative errno. */ + cmp r0, #-4096 + neghi r0, r0 + bhi 1f +#elif defined(__FreeBSD__) + /* FreeBSD kernel returns positive errno and C bit set. */ + bcs 1f +#else +#error "unsupported os" +#endif + pop { r4, r5, r6, r7, r8, pc } + + /* code path when we didn't execute the syscall */ +2: mov r0, #QEMU_ERESTARTSYS + + /* code path setting errno */ +1: pop { r4, r5, r6, r7, r8, lr } + .cfi_adjust_cfa_offset -24 + .cfi_restore r4 + .cfi_restore r5 + .cfi_restore r6 + .cfi_restore r7 + .cfi_restore r8 + .cfi_restore lr + b safe_syscall_set_errno_tail + + .fnend + .cfi_endproc + .size safe_syscall_base, .-safe_syscall_base |