diff options
Diffstat (limited to 'common-user/host/i386/safe-syscall.inc.S')
| -rw-r--r-- | common-user/host/i386/safe-syscall.inc.S | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/common-user/host/i386/safe-syscall.inc.S b/common-user/host/i386/safe-syscall.inc.S new file mode 100644 index 0000000000..db2ed09839 --- /dev/null +++ b/common-user/host/i386/safe-syscall.inc.S @@ -0,0 +1,127 @@ +/* + * 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 + + /* 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: + .cfi_startproc + push %ebp + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset ebp, 0 + push %esi + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset esi, 0 + push %edi + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset edi, 0 + push %ebx + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset ebx, 0 + + /* The syscall calling convention isn't the same as the C one: + * we enter with 0(%esp) == return address + * 4(%esp) == &signal_pending + * 8(%esp) == syscall number + * 12(%esp) ... 32(%esp) == syscall arguments + * and return the result in eax + * and the syscall instruction needs + * eax == syscall number + * ebx, ecx, edx, esi, edi, ebp == syscall arguments + * and returns the result in eax + * Shuffle everything around appropriately. + * Note the 16 bytes that we pushed to save registers. + */ + mov 12+16(%esp), %ebx /* the syscall arguments */ + mov 16+16(%esp), %ecx + mov 20+16(%esp), %edx + mov 24+16(%esp), %esi + mov 28+16(%esp), %edi + mov 32+16(%esp), %ebp + + /* 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 */ + mov 4+16(%esp), %eax /* signal_pending */ + cmpl $0, (%eax) + jnz 2f + mov 8+16(%esp), %eax /* syscall number */ + int $0x80 +safe_syscall_end: + + /* code path for having successfully executed the syscall */ +#if defined(__linux__) + /* Linux kernel returns (small) negative errno. */ + cmp $-4095, %eax + jae 0f +#elif defined(__FreeBSD__) + /* FreeBSD kernel returns positive errno and C bit set. */ + jc 1f +#else +#error "unsupported os" +#endif + pop %ebx + .cfi_remember_state + .cfi_adjust_cfa_offset -4 + .cfi_restore ebx + pop %edi + .cfi_adjust_cfa_offset -4 + .cfi_restore edi + pop %esi + .cfi_adjust_cfa_offset -4 + .cfi_restore esi + pop %ebp + .cfi_adjust_cfa_offset -4 + .cfi_restore ebp + ret + .cfi_restore_state + +#if defined(__linux__) +0: neg %eax + jmp 1f +#endif + + /* code path when we didn't execute the syscall */ +2: mov $QEMU_ERESTARTSYS, %eax + + /* code path setting errno */ +1: pop %ebx + .cfi_adjust_cfa_offset -4 + .cfi_restore ebx + pop %edi + .cfi_adjust_cfa_offset -4 + .cfi_restore edi + pop %esi + .cfi_adjust_cfa_offset -4 + .cfi_restore esi + pop %ebp + .cfi_adjust_cfa_offset -4 + .cfi_restore ebp + mov %eax, 4(%esp) + jmp safe_syscall_set_errno_tail + + .cfi_endproc + .size safe_syscall_base, .-safe_syscall_base |