Messages in this thread | | | Date | Tue, 17 Jul 2012 11:08:23 +0900 | From | Masami Hiramatsu <> | Subject | Re: Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save_regs for i386 function calls |
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(2012/07/14 3:47), Steven Rostedt wrote: > On Thu, 2012-07-12 at 21:39 +0900, Masami Hiramatsu wrote: > >> /* >> * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode >> * when it traps. The previous stack will be directly underneath the saved >> * registers, and 'sp/ss' won't even have been saved. Thus the '®s->sp'. >> * >> * This is valid only for kernel mode traps. >> */ >> static inline unsigned long kernel_stack_pointer(struct pt_regs *regs) >> { >> #ifdef CONFIG_X86_32 >> return (unsigned long)(®s->sp); >> #else >> return regs->sp; >> #endif >> } > > I found that regs_get_register() doesn't honor this either. Thus, > kprobes in tracing gets this: > > # 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 >
Yes, that is by design, since I made it so. :) Instead of %sp, kprobe tracer provides $stack special argument for stack address, because "sp" is not always means the stack address on every arch.
Thanks,
-- 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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