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Re: [RFC][PATCH -tip 7/9] tracing: kprobe-tracer plugin supports arguments
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: Frederic Weisbecker <fweisbec at gmail dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, Steven Rostedt <rostedt at goodmis dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, systemtap-ml <systemtap at sources dot redhat dot com>, LKML <linux-kernel at vger dot kernel dot org>
- Date: Thu, 19 Mar 2009 23:40:17 -0400
- Subject: Re: [RFC][PATCH -tip 7/9] tracing: kprobe-tracer plugin supports arguments
- References: <49C2B4D0.8030904@redhat.com> <20090320005135.GC6895@nowhere>
Frederic Weisbecker wrote:
>> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
>> index 33bb355..e801e8c 100644
>> --- a/kernel/trace/trace_kprobe.c
>> +++ b/kernel/trace/trace_kprobe.c
>> @@ -27,15 +27,124 @@
>> #include <linux/types.h>
>> #include <linux/string.h>
>> #include <linux/ctype.h>
>> +#include <linux/ptrace.h>
>>
>> #include <linux/ftrace.h>
>> #include "trace.h"
>>
>> +/* TODO: Move these functions to arch/XXX/include/asm/ptrace.h */
>> +#define STACK_MASK (THREAD_SIZE - 1)
>> +#define valid_stack_addr(regs, addr) \
>> + (((addr) & ~STACK_MASK) == (kernel_trap_sp(regs) & ~STACK_MASK))
>> +
>> +#if defined(__i386__)
>> +#define MAX_REG_NUM 15
>> +#elif defined(__x86_64__)
>> +#define MAX_REG_NUM 21
>> +#else
>> +#define MAX_REG_NUM (sizeof(struct pt_regs)/sizeof(unsigned long))
>> +#endif
>> +
>> +static unsigned long fetch_register(struct pt_regs *regs, void *num)
>> +{
>> + if (unlikely((unsigned)num > MAX_REG_NUM))
>> + return 0;
>> + return *((unsigned long *)regs + (unsigned)num);
>> +}
>> +
>> +static unsigned long fetch_stack(struct pt_regs *regs, void *num)
>> +{
>> + unsigned long *addr = (unsigned long *)kernel_trap_sp(regs);
>> + addr += (unsigned)num;
>> + if (valid_stack_addr(regs, (unsigned long)addr))
>> + return *addr;
>> + else
>> + return 0;
>> +}
>> +
>> +static unsigned long fetch_memory(struct pt_regs *regs, void *addr)
>> +{
>> + unsigned long retval;
>> + probe_kernel_address(addr, retval);
>> + return retval;
>> +}
>
>
> It will return a random value.
ah, thanks. I'll check the retval of probe_kernel_address().
>> +
>> +#if defined(__i386__)
>> +#define REGPARMS 3
>> +static unsigned long fetch_argument(struct pt_regs *regs, void *data)
>> +{
>> + unsigned long n = (unsigned long)data;
>> + if (n > REGPARMS) {
>> + /*
>> + * The typical case: arg n is on the stack.
>> + * stack[0] = return address
>> + */
>> + return fetch_stack(regs, (void *)(n - REGPARMS));
>> + } else {
>> + switch (n) {
>> + case 1: return regs->ax;
>> + case 2: return regs->dx;
>> + case 3: return regs->cx;
>> + }
>> + return 0;
>> + }
>> +}
>> +#elif define(__x86_64__)
>> +#define REGPARMS 6
>
>
> These helpers could be defined in the appropriate arch directory.
> They may even be reused by further debugging engines.
Agreed. Since we don't have any those infrastructure (arch/*/lib/debug.c ?)
yet, I just put it in trace_kprobe.c.
Thank you,
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com