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Date: Wed, 7 Sep 2022 18:40:34 +0800 From: Jinyang He <hejinyang@...ngson.cn> To: Qing Zhang <zhangqing@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com> Cc: WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, Jiaxun Yang <jiaxun.yang@...goat.com>, Jeff Xie <xiehuan09@...il.com> Subject: Re: [PATCH v3 10/10] LoongArch/ftrace: Fix unwind state when option func_stack_trace On 2022/9/7 18:06, Qing Zhang wrote: > Ftrace plays like function head exception, prologue analysis will stop soon > because PC is at entry. > > 90000000004c5a54 <callee>: > 90000000004c5a54: 03400000 andi $zero, $zero, 0x0 ==>move t0, ra > 90000000004c5a58: 03400000 andi $zero, $zero, 0x0 ==>bl callsite > ==>90000000004c5a5c: 02fcc063 addi.d $sp, $sp, -208(0xf30) > ... > > When encountering ftrace_call, save trace function ra at PT_ERA, save parent ra > at PT_R1, At this time, pc is the position after the two nops of callee. There is > no conventional prologue operation between this position and the function entry, > so we need to resetthe first flag to make the caller continue to unwind. > > testing method: > echo path_openat > ./set_ftrace_filter > echo 1 > ./options/func_stack_trace > echo function > ./current_tracer > > Signed-off-by: Qing Zhang <zhangqing@...ngson.cn> > --- > arch/loongarch/include/asm/unwind.h | 2 +- > arch/loongarch/kernel/unwind_prologue.c | 33 +++++++++++++++++++++---- > 2 files changed, 29 insertions(+), 6 deletions(-) > > diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h > index f66b07c3e6a1..f2b52b9ea93d 100644 > --- a/arch/loongarch/include/asm/unwind.h > +++ b/arch/loongarch/include/asm/unwind.h > @@ -20,7 +20,7 @@ struct unwind_state { > char type; /* UNWINDER_XXX */ > struct stack_info stack_info; > struct task_struct *task; > - bool first, error; > + bool first, error, is_ftrace; > int graph_idx; > unsigned long sp, pc, ra; > }; > diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c > index 03f8b31a90cc..0bb19d3ae8ba 100644 > --- a/arch/loongarch/kernel/unwind_prologue.c > +++ b/arch/loongarch/kernel/unwind_prologue.c > @@ -14,9 +14,7 @@ unsigned long unwind_get_return_address(struct unwind_state *state) > > if (unwind_done(state)) > return 0; > - else if (state->type) > - return state->pc; > - else if (state->first) > + else if (state->type || state->first) > return state->pc; > > return *(unsigned long *)(state->sp); > @@ -42,16 +40,39 @@ static bool unwind_by_guess(struct unwind_state *state) > return false; > } > > +static void unwind_state_fixup(struct unwind_state *state) > +{ > + static unsigned long ftrace_case = (unsigned long)ftrace_call + 4; > + > + if (state->pc == ftrace_case) > + state->is_ftrace = true; > +} > + > static bool unwind_by_prologue(struct unwind_state *state) > { > struct stack_info *info = &state->stack_info; > union loongarch_instruction *ip, *ip_end; > unsigned long frame_size = 0, frame_ra = -1; > unsigned long size, offset, pc = state->pc; > + struct pt_regs *regs; > > if (state->sp >= info->end || state->sp < info->begin) > return false; > > + if (state->is_ftrace) { > + /* > + * As we meet ftrace_regs_entry, reset first flag like first doing > + * tracing, Prologue analysis will stop soon because PC is at entry. > + */ > + regs = (struct pt_regs *)state->sp; > + state->pc = regs->csr_era; > + state->ra = regs->regs[1]; > + state->sp = regs->regs[3]; > + state->first = true; > + state->is_ftrace = false; > + return true; > + } > + > if (!kallsyms_lookup_size_offset(pc, &size, &offset)) > return false; > > @@ -97,7 +118,7 @@ static bool unwind_by_prologue(struct unwind_state *state) > > state->pc = *(unsigned long *)(state->sp + frame_ra); > state->sp = state->sp + frame_size; > - return !!__kernel_text_address(state->pc); > + goto out; > > first: > state->first = false; > @@ -106,7 +127,9 @@ static bool unwind_by_prologue(struct unwind_state *state) > > state->pc = state->ra; > > - return !!__kernel_text_address(state->ra); > +out: > + unwind_state_fixup(state); > + return !!__kernel_text_address(state->pc); > } > > void unwind_start(struct unwind_state *state, struct task_struct *task, Hi, Qing Additional 'Reported-by: Jeff Xie <xiehuan09@...il.com>' is welcome. For this patch, Tested-by: Jinyang He <hejinyang@...ngson.cn>. Thanks, Jinyang
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