[PATCH 2/3] ARM: add TRACEHOOK support

[Will Deacon]

Hi Steven,

On Tue, Nov 29, 2011 at 04:28:14PM +0000, Steven Walter wrote:
> diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
> index 9726006..1411848 100644
> --- a/arch/arm/kernel/ptrace.c
> +++ b/arch/arm/kernel/ptrace.c
> @@ -22,6 +22,7 @@
>  #include <linux/perf_event.h>
>  #include <linux/hw_breakpoint.h>
>  #include <linux/regset.h>
> +#include <linux/tracehook.h>
>  
>  #include <asm/pgtable.h>
>  #include <asm/system.h>
> @@ -928,8 +929,6 @@ asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
>  
>  	if (!test_thread_flag(TIF_SYSCALL_TRACE))
>  		return scno;
> -	if (!(current->ptrace & PT_PTRACED))
> -		return scno;

This means that we can potentially corrupt current_thread_info()->syscall
for tasks that aren't being traced. I don't think that matters as it's only
used by ptrace, but worth bearing in mind.

>  	/*
>  	 * Save IP.  IP is used to denote syscall entry/exit:
> @@ -940,19 +939,13 @@ asmlinkage int syscall_trace(int why, struct pt_regs *regs, int scno)
>  
>  	current_thread_info()->syscall = scno;
>  
> -	/* the 0x80 provides a way for the tracing parent to distinguish
> -	   between a syscall stop and SIGTRAP delivery */
> -	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
> -				 ? 0x80 : 0));
> -	/*
> -	 * this isn't the same as continuing with a signal, but it will do
> -	 * for normal use.  strace only continues with a signal if the
> -	 * stopping signal is not SIGTRAP.  -brl
> -	 */
> -	if (current->exit_code) {
> -		send_sig(current->exit_code, current, 1);
> -		current->exit_code = 0;
> +	if (why == 0) {
> +		if (tracehook_report_syscall_entry(regs))
> +			current_thread_info()->syscall = -1;

Why do you set syscall to -1 here? It looks like
tracehook_report_syscall_entry always returns 0, but even so, I'm not sure
what this -1 represents. You could also rewrite this a bit more neatly:

if (why)
	tracehook_report_syscall_exit(...);
else
	tracehook_report_syscall_entry(...);


> +	} else {
> +		tracehook_report_syscall_exit(regs, 0);
>  	}
> +
>  	regs->ARM_ip = ip;
>  
>  	return current_thread_info()->syscall;
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index 0340224..26c26f5 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -645,6 +645,8 @@ handle_signal(unsigned long sig, struct k_sigaction *ka,
>  	recalc_sigpending();
>  	spin_unlock_irq(&tsk->sighand->siglock);
>  
> +	tracehook_signal_handler(sig, info, ka, regs, 0);
> +

This doesn't appear to do anything but I guess that's where it should live.

Will