[PATCH v11 3/8] ARM: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

[Donglin Peng]

On 2023/6/9 9:57, Steven Rostedt wrote:
> On Sat,  8 Apr 2023 05:42:17 -0700
> Donglin Peng <pengdonglin at sangfor.com.cn> wrote:
> 
>> The previous patch ("function_graph: Support recording and printing
>> the return value of function") has 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 at sangfor.com.cn>
> 
> I really don't want to add this without an ack from an arm maintainer.
> 
> I have the patches queued (for testing), but I may remove the ones that do
> not have the appropriate acks.
> 
> -- Steve
> 

Hi Russell, can I get a ack for arm?

> 
>> ---
>> v10:
>>   - Use CONFIG_FUNCTION_GRAPH_TRACER to control fgraph_ret_regs definition
>>
>> v9:
>>   - Fix stack pointer align issues
>>   - Update the commit message
>>
>> v8:
>>   - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
>> ---
>>   arch/arm/Kconfig               |  1 +
>>   arch/arm/include/asm/ftrace.h  | 22 ++++++++++++++++++++++
>>   arch/arm/kernel/asm-offsets.c  |  8 +++++++-
>>   arch/arm/kernel/entry-ftrace.S | 10 ++++++----
>>   4 files changed, 36 insertions(+), 5 deletions(-)
>>
>> 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..3c457902b355 100644
>> --- a/arch/arm/include/asm/ftrace.h
>> +++ b/arch/arm/include/asm/ftrace.h
>> @@ -77,4 +77,26 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
>>   
>>   #endif /* ifndef __ASSEMBLY__ */
>>   
>> +#ifndef __ASSEMBLY__
>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> +struct fgraph_ret_regs {
>> +	/* r0 - r3 */
>> +	unsigned long regs[4];
>> +
>> +	unsigned long fp;
>> +	unsigned long __unused;
>> +};
>> +
>> +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 /* ifdef CONFIG_FUNCTION_GRAPH_TRACER */
>> +#endif
>> +
>>   #endif /* _ASM_ARM_FTRACE */
>> diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
>> index 38121c59cbc2..18bb85115b21 100644
>> --- a/arch/arm/kernel/asm-offsets.c
>> +++ b/arch/arm/kernel/asm-offsets.c
>> @@ -23,6 +23,7 @@
>>   #include <asm/suspend.h>
>>   #include <asm/vdso_datapage.h>
>>   #include <asm/hardware/cache-l2x0.h>
>> +#include <asm/ftrace.h>
>>   #include <linux/kbuild.h>
>>   #include <linux/arm-smccc.h>
>>   #include "signal.h"
>> @@ -170,5 +171,10 @@ int main(void)
>>     DEFINE(KEXEC_INDIR_PAGE,	offsetof(struct kexec_relocate_data, kexec_indirection_page));
>>     DEFINE(KEXEC_MACH_TYPE,	offsetof(struct kexec_relocate_data, kexec_mach_type));
>>     DEFINE(KEXEC_R2,		offsetof(struct kexec_relocate_data, kexec_r2));
>> -  return 0;
>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> +  BLANK();
>> +  DEFINE(FGRET_REGS_SIZE,	sizeof(struct fgraph_ret_regs));
>> +  BLANK();
>> +#endif
>> +  return 0;
>>   }
>> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
>> index 3e7bcaca5e07..d41a1676608c 100644
>> --- a/arch/arm/kernel/entry-ftrace.S
>> +++ b/arch/arm/kernel/entry-ftrace.S
>> @@ -257,11 +257,13 @@ ENDPROC(ftrace_graph_regs_caller)
>>   
>>   #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>   ENTRY(return_to_handler)
>> -	stmdb	sp!, {r0-r3}
>> -	add	r0, sp, #16		@ sp at exit of instrumented routine
>> +	mov	ip, sp				@ sp at exit of instrumented routine
>> +	stmdb	sp!, {r0-r3, ip, lr}		@ fill fgraph_ret_regs
>> +	mov	r0, sp
>>   	bl	ftrace_return_to_handler
>> -	mov	lr, r0			@ r0 has real ret addr
>> -	ldmia	sp!, {r0-r3}
>> +	mov	lr, r0				@ r0 has real ret addr
>> +	ldmia	sp, {r0-r3}
>> +	add	sp, sp, #FGRET_REGS_SIZE	@ restore stack pointer
>>   	ret	lr
>>   ENDPROC(return_to_handler)
>>   #endif
>