On Mon, Aug 06, 2012 at 06:05:30PM +0200, Richard Weinberger wrote:
> Hmm, is it a good idea to call syscall_trace_leave() in any case?
> E.g. if syscall_trace_enter() fails for whatever reason...
I have replicated the behavior of other architectures.
For example in x86/32 a.k.a. i386:
arch/x86/kernel/entry_32.S:
489 ENTRY(system_call)
490 RING0_INT_FRAME # can't unwind into user space anyway
491 pushl_cfi %eax # save orig_eax
492 SAVE_ALL
493 GET_THREAD_INFO(%ebp)
494 # system call tracing in operation / emulation
495 testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%ebp)
496 jnz syscall_trace_entry
497 cmpl $(NR_syscalls), %eax
498 jae syscall_badsys
499 syscall_call:
500 call *sys_call_table(,%eax,4)
501 movl %eax,PT_EAX(%esp) # store the return value
502 syscall_exit:
503 LOCKDEP_SYS_EXIT
504 DISABLE_INTERRUPTS(CLBR_ANY) # make sure we don't miss an interrupt
505 # setting need_resched or sigpending
506 # between sampling and the iret
507 TRACE_IRQS_OFF
508 movl TI_flags(%ebp), %ecx
509 testl $_TIF_ALLWORK_MASK, %ecx # current->work
510 jne syscall_exit_work
....
647 syscall_trace_entry:
648 movl $-ENOSYS,PT_EAX(%esp)
649 movl %esp, %eax
650 call syscall_trace_enter
651 /* What it returned is what we'll actually use. */
652 cmpl $(NR_syscalls), %eax
653 jnae syscall_call
654 jmp syscall_exit
655 END(syscall_trace_entry)
....
659 syscall_exit_work:
660 testl $_TIF_WORK_SYSCALL_EXIT, %ecx
661 jz work_pending
662 TRACE_IRQS_ON
663 ENABLE_INTERRUPTS(CLBR_ANY) # could let syscall_trace_leave() call
664 # schedule() instead
665 movl %esp, %eax
666 call syscall_trace_leave
667 jmp resume_userspace
as you can see:
if the process is traced line 496 jumps to syscall_trace_entry:
if syscall_trace_entry returns nonzero (line 652-654) jumps to syscall_exit
(skipping the
system call) otherwise returns to syscall_call.
whatever is the return value of syscall_trace_enter, if the process is traced
(line 510: it jumps to syscall_exit_work) and then it will call
syscall_trace_leave.
So I think we must replicate the same beavior for user-mode linux, too.
renzo
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