get_nr_restart_syscall() checks TS_I386_REGS_POKED but this bit is only set if debugger is 32-bit. If a 64-bit debugger restores the registers of a 32-bit debugee outside of syscall exit path get_nr_restart_syscall() wrongly returns __NR_restart_syscall.
Test-case: $ cvs -d :pserver:anoncvs:anon...@sourceware.org:/cvs/systemtap co ptrace-tests $ gcc -o erestartsys-trap-debuggee ptrace-tests/tests/erestartsys-trap-debuggee.c --m32 $ gcc -o erestartsys-trap-debugger ptrace-tests/tests/erestartsys-trap-debugger.c -lutil $ ./erestartsys-trap-debugger Unexpected: retval 1, errno 22 erestartsys-trap-debugger: ptrace-tests/tests/erestartsys-trap-debugger.c:421 As Jan explains this is what "(gdb) call func()" actually does: * Tracee calls sleep(2). * Debugger interrupts the tracee by CTRL-C after 1 sec. * Save regs by PTRACE_GETREGS. * Use PTRACE_SETREGS changing %rip to some 'func' and setting %orig_rax=-1 * PTRACE_CONT * func() uses int3. * Debugger catches SIGTRAP. * Restore original regs by PTRACE_SETREGS. * PTRACE_CONT Change get_nr_restart_syscall() to take __USER32_CS into account, to me this looks a bit better than TIF_IA32 check but either way this logic can't be always right as the comment explains. Alternatively we could change putreg() to set TS_I386_REGS_POKED just like putreg32() does if "child" is 32-bit, but this won't fix all the problems too and I think it would be beter to kill TS_I386_REGS_POKED after this change. Reported-by: Jan Kratochvil <jan.kratoch...@redhat.com> Signed-off-by: Oleg Nesterov <o...@redhat.com> Cc: sta...@vger.kernel.org --- arch/x86/kernel/signal.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c index 763af1d..1b05448 100644 --- a/arch/x86/kernel/signal.c +++ b/arch/x86/kernel/signal.c @@ -785,7 +785,8 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs) * than the tracee. */ #ifdef CONFIG_IA32_EMULATION - if (current->thread.status & (TS_COMPAT|TS_I386_REGS_POKED)) + if ((current->thread.status & (TS_COMPAT|TS_I386_REGS_POKED)) || + regs->cs == __USER32_CS) return __NR_ia32_restart_syscall; #endif #ifdef CONFIG_X86_X32_ABI -- 2.5.0