diff options
Diffstat (limited to 'linux-user/host/x86_64/safe-syscall.inc.S')
| -rw-r--r-- | linux-user/host/x86_64/safe-syscall.inc.S | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/linux-user/host/x86_64/safe-syscall.inc.S b/linux-user/host/x86_64/safe-syscall.inc.S new file mode 100644 index 0000000000..dde434c8d7 --- /dev/null +++ b/linux-user/host/x86_64/safe-syscall.inc.S @@ -0,0 +1,81 @@ +/* + * 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 + * + * Copyright (C) 2015 Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk> + * + * 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: + /* This saves a frame pointer and aligns the stack for the syscall. + * (It's unclear if the syscall ABI has the same stack alignment + * requirements as the userspace function call ABI, but better safe than + * sorry. Appendix A2 of http://www.x86-64.org/documentation/abi.pdf + * does not list any ABI differences regarding stack alignment.) + */ + push %rbp + + /* The syscall calling convention isn't the same as the + * C one: + * we enter with rdi == *signal_pending + * rsi == syscall number + * rdx, rcx, r8, r9, (stack), (stack) == syscall arguments + * and return the result in rax + * and the syscall instruction needs + * rax == syscall number + * rdi, rsi, rdx, r10, r8, r9 == syscall arguments + * and returns the result in rax + * Shuffle everything around appropriately. + * Note that syscall will trash rcx and r11. + */ + mov %rsi, %rax /* syscall number */ + mov %rdi, %rbp /* signal_pending pointer */ + /* and the syscall arguments */ + mov %rdx, %rdi + mov %rcx, %rsi + mov %r8, %rdx + mov %r9, %r10 + mov 16(%rsp), %r8 + mov 24(%rsp), %r9 + + /* 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 */ + testl $1, (%rbp) + jnz return_ERESTARTSYS + syscall +safe_syscall_end: + /* code path for having successfully executed the syscall */ + pop %rbp + ret + +return_ERESTARTSYS: + /* code path when we didn't execute the syscall */ + mov $-TARGET_ERESTARTSYS, %rax + pop %rbp + ret + + .size safe_syscall_base, .-safe_syscall_base |