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SubjectRe: [PATCH v8 3/8] ARM: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL
On Tue, Mar 28, 2023 at 06:43:14AM -0700, Donglin Peng wrote:
> The commit d4815c5d1bbd ("function_graph: Support recording and printing
> the return value of function") laid the groundwork for the for the
> funcgraph-retval, and this modification makes it available on the
> ARM platform.
>
> We introduce a new structure called fgraph_ret_regs for the ARM platform
> to hold return registers and the frame pointer. We then fill its content
> in the return_to_handler and pass its address to the function
> ftrace_return_to_handler to record the return value.
>
> Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
> ---
> v8:
> - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
> ---
> arch/arm/Kconfig | 1 +
> arch/arm/include/asm/ftrace.h | 18 ++++++++++++++++++
> arch/arm/kernel/entry-ftrace.S | 6 +++++-
> 3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index e24a9820e12f..73061379855a 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -98,6 +98,7 @@ config ARM
> select HAVE_FAST_GUP if ARM_LPAE
> select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> select HAVE_FUNCTION_ERROR_INJECTION
> + select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
> select HAVE_FUNCTION_GRAPH_TRACER
> select HAVE_FUNCTION_TRACER if !XIP_KERNEL
> select HAVE_GCC_PLUGINS
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index 7e9251ca29fe..2ab4bee21d79 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -77,4 +77,22 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
>
> #endif /* ifndef __ASSEMBLY__ */
>
> +
> +#ifndef __ASSEMBLY__
> +struct fgraph_ret_regs {
> + unsigned long regs[4];
> + unsigned long fp;
> +};
> +
> +static inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
> +{
> + return ret_regs->regs[0];
> +}
> +
> +static inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
> +{
> + return ret_regs->fp;
> +}
> +#endif
> +
> #endif /* _ASM_ARM_FTRACE */
> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
> index 3e7bcaca5e07..5f1e74555b25 100644
> --- a/arch/arm/kernel/entry-ftrace.S
> +++ b/arch/arm/kernel/entry-ftrace.S
> @@ -257,11 +257,15 @@ ENDPROC(ftrace_graph_regs_caller)
>
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> ENTRY(return_to_handler)
> + sub sp, sp, #4
> stmdb sp!, {r0-r3}
> - add r0, sp, #16 @ sp at exit of instrumented routine
> + add r0, sp, #20 @ sp at exit of instrumented routine
> + str r0, [sp, #16]
> + mov r0, sp

1) EABI wants the stack to be aligned to 8 bytes.
2) We can do better than this.

mov ip, sp
stmdb sp!, {r0-r3, ip, lr}
mov r0, sp

> bl ftrace_return_to_handler
> mov lr, r0 @ r0 has real ret addr
> ldmia sp!, {r0-r3}

ldmia sp, {r0-r3} @ since we need to manually adjust sp,

> + add sp, sp, #4 @ skip fp

add sp, sp, #4 * 6 @ restore stack pointer here

> ret lr
> ENDPROC(return_to_handler)
> #endif
> --
> 2.25.1
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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