Re: [PATCH v4 1/2] function_graph: Support recording and printing the return value of function
From: Peter Zijlstra <peterz@infradead.org>
Date: 2023-03-15 15:00:29
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linux-arm-kernel, linux-riscv, lkml
On Wed, Mar 15, 2023 at 10:13:48AM -0400, Steven Rostedt wrote:
On Wed, 15 Mar 2023 14:49:11 +0100 Peter Zijlstra [off-list ref] wrote:quoted
quoted
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_handlerWhat 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.