diff options
Diffstat (limited to 'linux-user/host/i386/safe-syscall.inc.S')
| -rw-r--r-- | linux-user/host/i386/safe-syscall.inc.S | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/linux-user/host/i386/safe-syscall.inc.S b/linux-user/host/i386/safe-syscall.inc.S new file mode 100644 index 0000000000..9d98332148 --- /dev/null +++ b/linux-user/host/i386/safe-syscall.inc.S @@ -0,0 +1,134 @@ +/* + * 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 linux-user/safe-syscall.S + * + * * Written by Peter Maydell <peter.maydell@linaro.org> + * + * Copyright (C) 2016 Linaro Limited + * + * 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'). + * We return a long which is the syscall's return value, which + * may be negative-errno on failure. Conversion to the + * -1-and-errno-set convention is done by the calling wrapper. + */ +safe_syscall_base: + .cfi_startproc + /* Save ebx esi edi ebp, as the calling convention requires */ + pushl %ebp + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset ebp, 0 + pushl %edi + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset edi, 0 + pushl %esi + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset esi, 0 + pushl %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 all arguments on the stack: + * *signal_pending + * syscall number + * 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. + * + * At this point the stack layout is: + * 48(%esp) syscall arg 6 + * 44(%esp) syscall arg 5 + * 40(%esp) syscall arg 4 + * 36(%esp) syscall arg 3 + * 32(%esp) syscall arg 2 + * 28(%esp) syscall arg 1 + * 24(%esp) syscall number + * 20(%esp) *signal_pending + * 16(%esp) return address + * 12(%esp) saved EBP + * 8(%esp) saved EDI + * 4(%esp) saved ESI + * (%esp) saved EBX + */ + /* syscall arguments */ + movl 48(%esp), %ebp + movl 44(%esp), %edi + movl 40(%esp), %esi + movl 36(%esp), %edx + movl 32(%esp), %ecx + movl 28(%esp), %ebx + + /* 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. + * For i386 we have absolutely no spare registers at the point of + * the syscall, so we must load *signal_pending and the syscall + * number off the stack inside the start/end section. + */ +safe_syscall_start: + /* *signal_pending */ + movl 20(%esp), %eax + /* if signal_pending is non-zero, don't do the call */ + testl $1, (%eax) + jnz return_ERESTARTSYS + movl 24(%esp), %eax + int $0x80 +safe_syscall_end: + /* code path for having successfully executed the syscall */ + .cfi_remember_state + popl %ebx + .cfi_adjust_cfa_offset -4 + .cfi_restore ebx + popl %esi + .cfi_adjust_cfa_offset -4 + .cfi_restore esi + popl %edi + .cfi_adjust_cfa_offset -4 + .cfi_restore edi + popl %ebp + .cfi_adjust_cfa_offset -4 + .cfi_restore ebp + ret + +return_ERESTARTSYS: + /* code path when we didn't execute the syscall */ + .cfi_restore_state + mov $-TARGET_ERESTARTSYS, %eax + popl %ebx + .cfi_adjust_cfa_offset -4 + .cfi_restore ebx + popl %esi + .cfi_adjust_cfa_offset -4 + .cfi_restore esi + popl %edi + .cfi_adjust_cfa_offset -4 + .cfi_restore edi + popl %ebp + .cfi_adjust_cfa_offset -4 + .cfi_restore ebp + ret + .cfi_endproc + + .size safe_syscall_base, .-safe_syscall_base |