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Date: Wed, 26 Apr 2023 22:30:51 +0800
From: Youling Tang <tangyouling@...ngson.cn>
To: Mark Rutland <mark.rutland@....com>
Cc: Huacai Chen <chenhuacai@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
WANG Xuerui <kernel@...0n.name>, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
loongson-kernel@...ts.loongnix.cn,
Qing Zhang <zhangqing@...ngson.cn>
Subject: Re: [PATCH 3/5] LoongArch: ftrace: Add direct call support
Hi, Mark
On 2023/4/26 21:43, Mark Rutland wrote:
> Hi,
>
> On Wed, Apr 26, 2023 at 09:49:12AM +0800, Youling Tang wrote:
>> select the DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide the
>> register_ftrace_direct[_multi] interfaces allowing users to register
>> the customed trampoline (direct_caller) as the mcount for one or
>> more target functions. And modify_ftrace_direct[_multi] are also
>> provided for modifying direct_caller.
>>
>> There are a few cases to distinguish:
>> - If a direct call ops is the only one tracing a function:
>> - If the direct called trampoline is within the reach of a 'bl'
>> instruction
>> -> the ftrace patchsite jumps to the trampoline
>> - Else
>> -> the ftrace patchsite jumps to the ftrace_regs_caller trampoline
>> which reads the ops pointer in the patchsite and jumps to the
>> direct call address stored in the ops
> I think you forgot to update this wording; there's no ops pointer in the
> patchsite as you don't implement DYNAMIC_FTRACE_WITH_CALL_OPS.
>
> I think you can delete the "Else" case here, and replace the above with:
>
> - If a direct call ops is the only one tracing a function AND the direct called
> trampoline is within the reach of a 'bl' instruction
> -> the ftrace patchsite jumps to the trampoline
>
>> - Else
>> -> the ftrace patchsite jumps to the ftrace_regs_caller trampoline and
>> its ops literal points to ftrace_list_ops so it iterates over all
>> registered ftrace ops, including the direct call ops and calls its
>> call_direct_funcs handler which stores the direct called trampoline's
>> address in the ftrace_regs and the ftrace_regs_caller trampoline will
> Likewise here, there's no "ops literal" associated with the patchsite.
Yes, thank you for pointing out, I will fix this description.
Thanks,
Youling.
>
> Otherwise, this looks sane to me.
>
> Mark.
>
>> return to that address instead of returning to the traced function
>>
>> Signed-off-by: Qing Zhang <zhangqing@...ngson.cn>
>> Signed-off-by: Youling Tang <tangyouling@...ngson.cn>
>> ---
>> arch/loongarch/Kconfig | 1 +
>> arch/loongarch/include/asm/ftrace.h | 12 ++++++++++++
>> arch/loongarch/kernel/ftrace_dyn.c | 8 ++++++++
>> arch/loongarch/kernel/mcount_dyn.S | 7 ++++++-
>> 4 files changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> index 3ddde336e6a5..d6068a88d53f 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -92,6 +92,7 @@ config LOONGARCH
>> select HAVE_DMA_CONTIGUOUS
>> select HAVE_DYNAMIC_FTRACE
>> select HAVE_DYNAMIC_FTRACE_WITH_ARGS
>> + select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>> select HAVE_DYNAMIC_FTRACE_WITH_REGS
>> select HAVE_EBPF_JIT
>> select HAVE_EFFICIENT_UNALIGNED_ACCESS if !ARCH_STRICT_ALIGN
>> diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
>> index 3418d32d4fc7..f789e680f633 100644
>> --- a/arch/loongarch/include/asm/ftrace.h
>> +++ b/arch/loongarch/include/asm/ftrace.h
>> @@ -57,6 +57,18 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
>> #define ftrace_graph_func ftrace_graph_func
>> void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
>> struct ftrace_ops *op, struct ftrace_regs *fregs);
>> +
>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>> +static inline void
>> +__arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
>> +{
>> + regs->regs[13] = addr; /* t1 */
>> +}
>> +
>> +#define arch_ftrace_set_direct_caller(fregs, addr) \
>> + __arch_ftrace_set_direct_caller(&(fregs)->regs, addr)
>> +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
>> +
>> #endif
>>
>> #endif /* __ASSEMBLY__ */
>> diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
>> index 3cc4f8159f48..4062a7e63137 100644
>> --- a/arch/loongarch/kernel/ftrace_dyn.c
>> +++ b/arch/loongarch/kernel/ftrace_dyn.c
>> @@ -66,6 +66,14 @@ static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod
>> unsigned long pc = rec->ip + LOONGARCH_INSN_SIZE;
>> struct plt_entry *plt;
>>
>> + /*
>> + * If a custom trampoline is unreachable, rely on the ftrace_regs_caller
>> + * trampoline which knows how to indirectly reach that trampoline
>> + * through ops->direct_call.
>> + */
>> + if (*addr != FTRACE_ADDR && *addr != FTRACE_REGS_ADDR && !reachable_by_bl(*addr, pc))
>> + *addr = FTRACE_REGS_ADDR;
>> +
>> /*
>> * When the target is within range of the 'bl' instruction, use 'addr'
>> * as-is and branch to that directly.
>> diff --git a/arch/loongarch/kernel/mcount_dyn.S b/arch/loongarch/kernel/mcount_dyn.S
>> index bbabf06244c2..1008fbc3cabc 100644
>> --- a/arch/loongarch/kernel/mcount_dyn.S
>> +++ b/arch/loongarch/kernel/mcount_dyn.S
>> @@ -42,7 +42,6 @@
>> .if \allregs
>> PTR_S tp, sp, PT_R2
>> PTR_S t0, sp, PT_R12
>> - PTR_S t1, sp, PT_R13
>> PTR_S t2, sp, PT_R14
>> PTR_S t3, sp, PT_R15
>> PTR_S t4, sp, PT_R16
>> @@ -64,6 +63,8 @@
>> PTR_S zero, sp, PT_R0
>> .endif
>> PTR_S ra, sp, PT_ERA /* Save trace function ra at PT_ERA */
>> + move t1, zero
>> + PTR_S t1, sp, PT_R13
>> PTR_ADDI t8, sp, PT_SIZE
>> PTR_S t8, sp, PT_R3
>> .endm
>> @@ -104,8 +105,12 @@ ftrace_common_return:
>> PTR_L a7, sp, PT_R11
>> PTR_L fp, sp, PT_R22
>> PTR_L t0, sp, PT_ERA
>> + PTR_L t1, sp, PT_R13
>> PTR_ADDI sp, sp, PT_SIZE
>> + bnez t1,.Ldirect
>> jr t0
>> +.Ldirect:
>> + jr t1
>> SYM_CODE_END(ftrace_common)
>>
>> SYM_CODE_START(ftrace_caller)
>> --
>> 2.37.1
>>
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