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x86: ptrace vs -ENOSYS 

When we're stopped at syscall entry tracing, ptrace can change the %rax
value from -ENOSYS to something else.  If no system call is actually made
because the syscall number (now in orig_rax) is bad, then we now always
reset %rax to -ENOSYS again.

This changes it to leave the return value alone after entry tracing.
That way, the %rax value set by ptrace is there to be seen in user mode
(or in syscall exit tracing).  This is consistent with what the 32-bit
kernel does.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Roland McGrath 2008-03-16 21:59:11 -07:00 committed by Ingo Molnar
parent 8ab32bb89b
commit a31f8dd7ee
1 changed files with 3 additions and 5 deletions
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8
arch/x86/kernel/entry_64.S
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@ -319,19 +319,17 @@ badsys:
/* Do syscall tracing */
tracesys:
SAVE_REST
movq $-ENOSYS,RAX(%rsp)
movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
FIXUP_TOP_OF_STACK %rdi
movq %rsp,%rdi
call syscall_trace_enter
LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */
RESTORE_REST
cmpq $__NR_syscall_max,%rax
movq $-ENOSYS,%rcx
cmova %rcx,%rax
ja 1f
ja int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */
movq %r10,%rcx /* fixup for C */
call *sys_call_table(,%rax,8)
1: movq %rax,RAX-ARGOFFSET(%rsp)
movq %rax,RAX-ARGOFFSET(%rsp)
/* Use IRET because user could have changed frame */
/*