[PATCH v2] riscv: stacktrace: Add USER_STACKTRACE support

[Jinjie Ruan]

On 2024/7/3 22:36, Björn Töpel wrote:
> Jinjie Ruan <ruanjinjie at huawei.com> writes:
> 
>> Currently, userstacktrace is unsupported for riscv. So use the
>> perf_callchain_user() code as blueprint to implement the
>> arch_stack_walk_user() which add userstacktrace support on riscv.
>> Meanwhile, we can use arch_stack_walk_user() to simplify the implementation
>> of perf_callchain_user().
>>
>> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
>> Reported-by: kernel test robot <lkp at intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202406012109.PDAjXm2i-lkp@intel.com/
> 
> For future reference: The LTP tags shouldn't be used when you're
> spinning a new version.

Thank you! I'll remove it.

> 
>> ---
>> v2:
>> - Fix the cocci warning, !A || A && B is equivalent to !A || B.
>> ---
>>  arch/riscv/Kconfig                 |  1 +
>>  arch/riscv/kernel/perf_callchain.c | 46 ++----------------------------
>>  arch/riscv/kernel/stacktrace.c     | 43 ++++++++++++++++++++++++++++
>>  3 files changed, 47 insertions(+), 43 deletions(-)
> 
> [...]
> 
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 0525ee2d63c7..6ed96d935b8f 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -193,6 +193,7 @@ config RISCV
>>  	select THREAD_INFO_IN_TASK
>>  	select TRACE_IRQFLAGS_SUPPORT
>>  	select UACCESS_MEMCPY if !MMU
>> +	select USER_STACKTRACE_SUPPORT
>>  	select ZONE_DMA32 if 64BIT
>>  
>>  config CLANG_SUPPORTS_DYNAMIC_FTRACE
>> diff --git a/arch/riscv/kernel/perf_callchain.c b/arch/riscv/kernel/perf_callchain.c
>> index 3348a61de7d9..c7468af77c66 100644
>> --- a/arch/riscv/kernel/perf_callchain.c
>> +++ b/arch/riscv/kernel/perf_callchain.c
>> @@ -6,37 +6,9 @@
>>  
>>  #include <asm/stacktrace.h>
>>  
>> -/*
>> - * Get the return address for a single stackframe and return a pointer to the
>> - * next frame tail.
>> - */
>> -static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
>> -				    unsigned long fp, unsigned long reg_ra)
>> +static bool fill_callchain(void *entry, unsigned long pc)
>>  {
>> -	struct stackframe buftail;
>> -	unsigned long ra = 0;
>> -	unsigned long __user *user_frame_tail =
>> -		(unsigned long __user *)(fp - sizeof(struct stackframe));
>> -
>> -	/* Check accessibility of one struct frame_tail beyond */
>> -	if (!access_ok(user_frame_tail, sizeof(buftail)))
>> -		return 0;
>> -	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
>> -				      sizeof(buftail)))
>> -		return 0;
>> -
>> -	if (reg_ra != 0)
>> -		ra = reg_ra;
>> -	else
>> -		ra = buftail.ra;
>> -
>> -	fp = buftail.fp;
>> -	if (ra != 0)
>> -		perf_callchain_store(entry, ra);
>> -	else
>> -		return 0;
>> -
>> -	return fp;
>> +	return perf_callchain_store(entry, pc) == 0;
>>  }
>>  
>>  /*
>> @@ -56,19 +28,7 @@ static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
>>  void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
>>  			 struct pt_regs *regs)
>>  {
>> -	unsigned long fp = 0;
>> -
>> -	fp = regs->s0;
>> -	perf_callchain_store(entry, regs->epc);
>> -
>> -	fp = user_backtrace(entry, fp, regs->ra);
>> -	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
>> -		fp = user_backtrace(entry, fp, 0);
>> -}
>> -
>> -static bool fill_callchain(void *entry, unsigned long pc)
>> -{
>> -	return perf_callchain_store(entry, pc) == 0;
>> +	arch_stack_walk_user(fill_callchain, entry, regs);
>>  }
>>  
>>  void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
>> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
>> index 528ec7cc9a62..9685a2baa5d9 100644
>> --- a/arch/riscv/kernel/stacktrace.c
>> +++ b/arch/riscv/kernel/stacktrace.c
>> @@ -161,3 +161,46 @@ noinline void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie
>>  {
>>  	walk_stackframe(task, regs, consume_entry, cookie);
>>  }
>> +
>> +/*
>> + * Get the return address for a single stackframe and return a pointer to the
>> + * next frame tail.
>> + */
>> +static unsigned long unwind_user_frame(stack_trace_consume_fn consume_entry,
>> +				       void *cookie, unsigned long fp,
>> +				       unsigned long reg_ra)
>> +{
>> +	struct stackframe buftail;
>> +	unsigned long ra = 0;
>> +	unsigned long __user *user_frame_tail =
>> +		(unsigned long __user *)(fp - sizeof(struct stackframe));
>> +
>> +	/* Check accessibility of one struct frame_tail beyond */
>> +	if (!access_ok(user_frame_tail, sizeof(buftail)))
>> +		return 0;
>> +	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
>> +				      sizeof(buftail)))
>> +		return 0;
>> +
>> +	ra = reg_ra ? : buftail.ra;
>> +
>> +	fp = buftail.fp;
>> +	if (!ra || !consume_entry(cookie, ra))
>> +		return 0;
>> +
>> +	return fp;
>> +}
>> +
>> +void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
>> +			  const struct pt_regs *regs)
>> +{
>> +	unsigned long fp = 0;
>> +
>> +	fp = regs->s0;
>> +	if (!consume_entry(cookie, regs->epc))
>> +		return;
>> +
>> +	fp = unwind_user_frame(consume_entry, cookie, fp, regs->ra);
>> +	while (fp && !(fp & 0x3))
> 
> Just an observation that the "entry->nr < entry->max_stack" check was
> removed in this generalization, but that's OK since it's checked in
> perf_callchain_store().

Yes, the checked is not necessary, because perf_callchain_store() check
"entry->nr < entry->max_stack"

Also the caller function stack_trace_save_user() registers the
consume_entry callback "stack_trace_consume_entry" for saving user stack
traces into a storage array, in which entry->nr against entry->max_stack
is put.

> 
> Not really part of your change, but shouldn't the check be 0x7 (checking
> for 16B sp/fp alignment), rather than 0x3?

You are right! From the below "RISCV Calling Convention" :

    "In the standard RISC-V calling convention, the stack grows downward

     and the stack pointer is always kept 16-byte aligned"

So the sp should be 16-byte aligned, and the "PT_SIZE_ON_STACK" is also
16-byte aligned, so I think the fp is also 16-byte aligned.

Link: https://riscv.org/wp-content/uploads/2015/01/riscv-calling.pdf
> 
> 
> Björn
> 
>