Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 16 Mar 2023 11:18:23 +0800 | From | Donglin Peng <> | Subject | Re: [PATCH v4 1/2] function_graph: Support recording and printing the return value of function |
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On 2023/3/15 22:57, Peter Zijlstra wrote: > On Wed, Mar 15, 2023 at 10:13:48AM -0400, Steven Rostedt wrote: >> On Wed, 15 Mar 2023 14:49:11 +0100 >> Peter Zijlstra <peterz@infradead.org> wrote: >> >>>> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S >>>> index 1265ad519249..35ac9c58dc77 100644 >>>> --- a/arch/x86/kernel/ftrace_64.S >>>> +++ b/arch/x86/kernel/ftrace_64.S >>>> @@ -348,6 +348,10 @@ SYM_CODE_START(return_to_handler) >>>> movq %rax, (%rsp) >>>> movq %rdx, 8(%rsp) >>>> movq %rbp, %rdi >>>> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL >>>> + /* Pass the function return value to ftrace_return_to_handler */ >>>> + movq %rax, %rsi >>>> +#endif >>>> >>>> call ftrace_return_to_handler >>> >>> What about the case of double register return values (when the value >>> is returned in the A,D pair) ? >> >> Is there anything that does that in 64 bit kernels? > > Note sure; but I have a patch series that introduces cmpxchg128 and > friends. Most of the actual functions are __always_inline, but still, > the moment a compiler decides to break out a subfunction on a u128 > boundary we're in luck. I have reviewed the kretprobe implementation and noticed that $retval only retrieves the value of pt_regs.ax, which is an unsigned long data type. I wrote a demo and tested it on an x86 machine, and found that $retval only shows the least significant 32 bits of retval.Therefore,I think it can be consistent with kretprobe.
static noinline unsigned long long test_retval_func(void) { unsigned long long value = 0x1234567887654321; return value; }
add a kretprobe event: echo 'r:myretprobe test_retval_func $retval:x64' > kprobe_events
the trace log: myretprobe: (retval_open+0x1c/0x2c [test_retval] <- test_retval_func) arg1=0x87654321
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