diff options
| -rw-r--r-- | linux-user/host/i386/hostdep.h | 23 | ||||
| -rw-r--r-- | linux-user/host/i386/safe-syscall.inc.S | 112 |
2 files changed, 135 insertions, 0 deletions
diff --git a/linux-user/host/i386/hostdep.h b/linux-user/host/i386/hostdep.h index 7609bf5cd7..5a12f4adce 100644 --- a/linux-user/host/i386/hostdep.h +++ b/linux-user/host/i386/hostdep.h @@ -12,4 +12,27 @@ #ifndef QEMU_HOSTDEP_H #define QEMU_HOSTDEP_H +/* We have a safe-syscall.inc.S */ +#define HAVE_SAFE_SYSCALL + +#ifndef __ASSEMBLER__ + +/* These are defined by the safe-syscall.inc.S file */ +extern char safe_syscall_start[]; +extern char safe_syscall_end[]; + +/* Adjust the signal context to rewind out of safe-syscall if we're in it */ +static inline void rewind_if_in_safe_syscall(void *puc) +{ + struct ucontext *uc = puc; + greg_t *pcreg = &uc->uc_mcontext.gregs[REG_EIP]; + + if (*pcreg > (uintptr_t)safe_syscall_start + && *pcreg < (uintptr_t)safe_syscall_end) { + *pcreg = (uintptr_t)safe_syscall_start; + } +} + +#endif /* __ASSEMBLER__ */ + #endif 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..766d0ded98 --- /dev/null +++ b/linux-user/host/i386/safe-syscall.inc.S @@ -0,0 +1,112 @@ +/* + * 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 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'). + * 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 + 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 */ + cmp $0, (%eax) + jnz 1f + mov 8+16(%esp), %eax /* syscall number */ + int $0x80 +safe_syscall_end: + /* code path for having successfully executed the syscall */ + pop %ebx + .cfi_remember_state + .cfi_def_cfa_offset -4 + .cfi_restore ebx + pop %edi + .cfi_def_cfa_offset -4 + .cfi_restore edi + pop %esi + .cfi_def_cfa_offset -4 + .cfi_restore esi + pop %ebp + .cfi_def_cfa_offset -4 + .cfi_restore ebp + ret + +1: + /* code path when we didn't execute the syscall */ + .cfi_restore_state + mov $-TARGET_ERESTARTSYS, %eax + pop %ebx + .cfi_def_cfa_offset -4 + .cfi_restore ebx + pop %edi + .cfi_def_cfa_offset -4 + .cfi_restore edi + pop %esi + .cfi_def_cfa_offset -4 + .cfi_restore esi + pop %ebp + .cfi_def_cfa_offset -4 + .cfi_restore ebp + ret + .cfi_endproc + + .size safe_syscall_base, .-safe_syscall_base |