Am 06.08.2012 17:37, schrieb Renzo Davoli:
> ---
> diff -Naur linux-3.6-rc1/arch/um/include/asm/ptrace-generic.h linux-3.6-rc1.tracehook/arch/um/include/asm/ptrace-generic.h
> --- linux-3.6-rc1/arch/um/include/asm/ptrace-generic.h	2012-08-03 01:38:10.000000000 +0200
> +++ linux-3.6-rc1.tracehook/arch/um/include/asm/ptrace-generic.h	2012-08-06 14:43:01.000000000 +0200
> @@ -37,7 +37,7 @@
>  
>  extern int arch_copy_tls(struct task_struct *new);
>  extern void clear_flushed_tls(struct task_struct *task);
> -extern void syscall_trace_enter(struct pt_regs *regs);
> +extern int syscall_trace_enter(struct pt_regs *regs);
>  extern void syscall_trace_leave(struct pt_regs *regs);
>  
>  #endif
> diff -Naur linux-3.6-rc1/arch/um/include/shared/kern_util.h linux-3.6-rc1.tracehook/arch/um/include/shared/kern_util.h
> --- linux-3.6-rc1/arch/um/include/shared/kern_util.h	2012-08-03 01:38:10.000000000 +0200
> +++ linux-3.6-rc1.tracehook/arch/um/include/shared/kern_util.h	2012-08-06 14:43:40.000000000 +0200
> @@ -57,7 +57,6 @@
>  extern unsigned long to_irq_stack(unsigned long *mask_out);
>  extern unsigned long from_irq_stack(int nested);
>  
> -extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
>  extern int singlestepping(void *t);
>  
>  extern void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs);
> diff -Naur linux-3.6-rc1/arch/um/kernel/ptrace.c linux-3.6-rc1.tracehook/arch/um/kernel/ptrace.c
> --- linux-3.6-rc1/arch/um/kernel/ptrace.c	2012-08-03 01:38:10.000000000 +0200
> +++ linux-3.6-rc1.tracehook/arch/um/kernel/ptrace.c	2012-08-06 14:45:07.000000000 +0200
> @@ -163,7 +163,7 @@
>   * XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
>   * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
>   */
> -void syscall_trace_enter(struct pt_regs *regs)
> +int syscall_trace_enter(struct pt_regs *regs)
>  {
>  	audit_syscall_entry(HOST_AUDIT_ARCH,
>  			    UPT_SYSCALL_NR(&regs->regs),
> @@ -173,9 +173,9 @@
>  			    UPT_SYSCALL_ARG4(&regs->regs));
>  
>  	if (!test_thread_flag(TIF_SYSCALL_TRACE))
> -		return;
> +		return 0;
>  
> -	tracehook_report_syscall_entry(regs);
> +	return tracehook_report_syscall_entry(regs);
>  }
>  
>  void syscall_trace_leave(struct pt_regs *regs)
> diff -Naur linux-3.6-rc1/arch/um/kernel/skas/syscall.c linux-3.6-rc1.tracehook/arch/um/kernel/skas/syscall.c
> --- linux-3.6-rc1/arch/um/kernel/skas/syscall.c	2012-08-03 01:38:10.000000000 +0200
> +++ linux-3.6-rc1.tracehook/arch/um/kernel/skas/syscall.c	2012-08-06 14:46:35.000000000 +0200
> @@ -18,23 +18,24 @@
>  	long result;
>  	int syscall;
>  
> -	syscall_trace_enter(regs);
> +	if (syscall_trace_enter(regs) == 0)
> +	{
> +		/*
> +		 * This should go in the declaration of syscall, but when I do that,
> +		 * strace -f -c bash -c 'ls ; ls' breaks, sometimes not tracing
> +		 * children at all, sometimes hanging when bash doesn't see the first
> +		 * ls exit.
> +		 * The assembly looks functionally the same to me.  This is
> +		 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
> +		 * in case it's a compiler bug.
> +		 */
> +		syscall = UPT_SYSCALL_NR(r);
> +		if ((syscall >= NR_SYSCALLS) || (syscall < 0))
> +			result = -ENOSYS;
> +		else result = EXECUTE_SYSCALL(syscall, regs);
>  
> -	/*
> -	 * This should go in the declaration of syscall, but when I do that,
> -	 * strace -f -c bash -c 'ls ; ls' breaks, sometimes not tracing
> -	 * children at all, sometimes hanging when bash doesn't see the first
> -	 * ls exit.
> -	 * The assembly looks functionally the same to me.  This is
> -	 *     gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
> -	 * in case it's a compiler bug.
> -	 */
> -	syscall = UPT_SYSCALL_NR(r);
> -	if ((syscall >= NR_SYSCALLS) || (syscall < 0))
> -		result = -ENOSYS;
> -	else result = EXECUTE_SYSCALL(syscall, regs);
> -
> -	PT_REGS_SET_SYSCALL_RETURN(regs, result);
> +		PT_REGS_SET_SYSCALL_RETURN(regs, result);
> +	}
>  
>  	syscall_trace_leave(regs);

Hmm, is it a good idea to call syscall_trace_leave() in any case?
E.g. if syscall_trace_enter() fails for whatever reason...

Thanks,
//richard