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SubjectRe: [RFC][PATCH] x86_32: Return actual stack when requesting sp from regs
(2012/07/14 4:44), Steven Rostedt wrote:
>
> As x86_32 traps do not save sp when taken in kernel mode, we need to
> accommodate the sp when requesting to get the register.
>
> This affects kprobes.
>
> Before:
>
> # echo 'p:ftrace sys_read+4 s=%sp' > /debug/tracing/kprobe_events
> # echo 1 > /debug/tracing/events/kprobes/enable
> # cat trace
> sshd-1345 [000] d... 489.117168: ftrace: (sys_read+0x4/0x70) s=b7e96768
> sshd-1345 [000] d... 489.117191: ftrace: (sys_read+0x4/0x70) s=b7e96768
> cat-1447 [000] d... 489.117392: ftrace: (sys_read+0x4/0x70) s=5a7
> cat-1447 [001] d... 489.118023: ftrace: (sys_read+0x4/0x70) s=b77ad05f
> less-1448 [000] d... 489.118079: ftrace: (sys_read+0x4/0x70) s=b7762e06
> less-1448 [000] d... 489.118117: ftrace: (sys_read+0x4/0x70) s=b7764970
>
> After:
> sshd-1352 [000] d... 362.348016: ftrace: (sys_read+0x4/0x70) s=f3febfa8
> sshd-1352 [000] d... 362.348048: ftrace: (sys_read+0x4/0x70) s=f3febfa8
> bash-1355 [001] d... 362.348081: ftrace: (sys_read+0x4/0x70) s=f5075fa8
> sshd-1352 [000] d... 362.348082: ftrace: (sys_read+0x4/0x70) s=f3febfa8
> sshd-1352 [000] d... 362.690950: ftrace: (sys_read+0x4/0x70) s=f3febfa8
> bash-1355 [001] d... 362.691033: ftrace: (sys_read+0x4/0x70) s=f5075fa8
>
> [ I wonder if this should also go to stable? ]
>

This obviously makes tracing output better on i386. Original %sp
gives nothing (or just misleading)...

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

NOTE: if someone needs to get kernel stack address from regs,
I recommend him to use kernel_stack_pointer() directly.

Thank you,

> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
>
> Index: linux-trace.git/arch/x86/include/asm/ptrace.h
> ===================================================================
> --- linux-trace.git.orig/arch/x86/include/asm/ptrace.h
> +++ linux-trace.git/arch/x86/include/asm/ptrace.h
> @@ -246,6 +246,15 @@ static inline unsigned long regs_get_reg
> {
> if (unlikely(offset > MAX_REG_OFFSET))
> return 0;
> +#ifdef CONFIG_X86_32
> + /*
> + * Traps from the kernel do not save sp and ss.
> + * Use the helper function to retrieve sp.
> + */
> + if (offset == offsetof(struct pt_regs, sp) &&
> + regs->cs == __KERNEL_CS)
> + return kernel_stack_pointer(regs);
> +#endif
> return *(unsigned long *)((unsigned long)regs + offset);
> }

--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com




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