[PATCH v3] ARM: support syscall tracing

[Will Deacon]

Hi Wade,

On Mon, Aug 20, 2012 at 03:38:37PM +0100, Wade Farnsworth wrote:
> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
> index 978eac5..b032c94 100644
> --- a/arch/arm/kernel/entry-common.S
> +++ b/arch/arm/kernel/entry-common.S
> @@ -94,6 +94,15 @@ ENDPROC(ret_from_fork)
>  	.equ NR_syscalls,0
>  #define CALL(x) .equ NR_syscalls,NR_syscalls+1
>  #include "calls.S"
> +
> +/*
> + * Ensure that the system call table is equal to __NR_syscalls,
> + * which is the value the rest of the system sees
> + */
> +.ifne NR_syscalls - __NR_syscalls
> +.error "__NR_syscalls is not equal to the size of the syscall table"
> +.endif
> +
>  #undef CALL
>  #define CALL(x) .long x
>  
> @@ -415,7 +424,7 @@ local_restart:
>  1:
>  #endif
>  
> -	tst	r10, #_TIF_SYSCALL_WORK		@ are we tracing syscalls?
> +	tst     r10, #_TIF_SYSCALL_WORK		@ are we tracing syscalls?

This is just a whitespace change, so I think you can drop it.

> diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
> index 3e0fc5f..4974cdf 100644
> --- a/arch/arm/kernel/ptrace.c
> +++ b/arch/arm/kernel/ptrace.c
> @@ -30,6 +30,9 @@
>  #include <asm/pgtable.h>
>  #include <asm/traps.h>
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/syscalls.h>
> +
>  #define REG_PC	15
>  #define REG_PSR	16
>  /*
> @@ -918,11 +921,11 @@ static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
>  {
>  	unsigned long ip;
>  
> +	current_thread_info()->syscall = scno;
> +
>  	if (!test_thread_flag(TIF_SYSCALL_TRACE))
>  		return scno;
>  
> -	current_thread_info()->syscall = scno;
> -
>  	/*
>  	 * IP is used to denote syscall entry/exit:
>  	 * IP = 0 -> entry, =1 -> exit
> @@ -942,6 +945,8 @@ static int ptrace_syscall_trace(struct pt_regs *regs, int scno,
>  asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
>  {
>  	int ret = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_ENTER);
> +	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
> +		trace_sys_enter(regs, scno);
>  	audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0, regs->ARM_r1,
>  			    regs->ARM_r2, regs->ARM_r3);
>  	return ret;
> @@ -950,6 +955,8 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
>  asmlinkage int syscall_trace_exit(struct pt_regs *regs, int scno)
>  {
>  	int ret = ptrace_syscall_trace(regs, scno, PTRACE_SYSCALL_EXIT);
> +	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
> +		trace_sys_exit(regs, scno);

I think that trace_sys_{enter,exit} should take ret rather than scno. A
debugger could change the syscall number if TIF_SYSCALL_TRACE is set and
that new number should be the one that we use.

The style, however, is much better and I think the code is fairly clear now
so we just need to wait for my fix to the core code to get merged (it got
picked up by Steve Rostedt) and I think we can use ret directly. It might be
worth dropping the local variable and using scno for everything, so that
it's obvious where the syscall number is stored.

Will