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Subject[PATCH 1/2] x86_64 ia32 ptrace vs -ENOSYS
Date

When we're stopped at syscall entry tracing, ptrace can change the %eax
value from -ENOSYS to something else. If no system call is actually made
because the syscall number (now in orig_eax) is bad, then the %eax value
set by ptrace should be returned to the user. But, instead it gets reset
to -ENOSYS again. This is a regression from the native 32-bit kernel.

This change fixes it by leaving the return value alone after entry tracing.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
arch/x86/ia32/ia32entry.S | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index b42d009..eafb0b9 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -325,7 +325,7 @@ ENTRY(ia32_syscall)
jnz ia32_tracesys
ia32_do_syscall:
cmpl $(IA32_NR_syscalls-1),%eax
- ja ia32_badsys
+ ja int_ret_from_sys_call /* ia32_tracesys has set RAX(%rsp) */
IA32_ARG_FIXUP
call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
ia32_sysret:
@@ -335,7 +335,7 @@ ia32_sysret:
ia32_tracesys:
SAVE_REST
CLEAR_RREGS
- movq $-ENOSYS,RAX(%rsp) /* really needed? */
+ movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
movq %rsp,%rdi /* &pt_regs -> arg1 */
call syscall_trace_enter
LOAD_ARGS32 ARGOFFSET /* reload args from stack in case ptrace changed it */

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