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Subject: Re: [PATCH v6 3/9] LoongArch/ftrace: Add dynamic function tracer
 support
To:     Huacai Chen <chenhuacai@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org, Jinyang He <hejinyang@loongson.cn>
References: <20221115025527.13382-1-zhangqing@loongson.cn>
 <20221115025527.13382-4-zhangqing@loongson.cn>
 <CAAhV-H41XxvVhtkL3WhHH_iFVWu1E28dPNZAbNCOgtrzfrZmpQ@mail.gmail.com>
From:   Qing Zhang <zhangqing@loongson.cn>
Message-ID: <89b91939-5618-35ff-24c3-d4f76ecf46b2@loongson.cn>
Date:   Tue, 15 Nov 2022 19:11:48 +0800
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Hi, huacai

On 2022/11/15 下午6:54, Huacai Chen wrote:
> Hi, Qing,
> 
> On Tue, Nov 15, 2022 at 10:55 AM Qing Zhang <zhangqing@loongson.cn> wrote:
>>
>> The compiler has inserted 2 NOPs before the regular function prologue.
>> T series registers are available and safe because of LoongArch psABI.
>>
>> At runtime, replace nop with bl to enable ftrace call and replace bl with
>> nop to disable ftrace call. The bl requires us to save the original RA
>> value, so here it saves RA at t0.
>> details are:
>>
>> | Compiled   |       Disabled         |        Enabled         |
>> +------------+------------------------+------------------------+
>> | nop        | move     t0, ra        | move     t0, ra        |
>> | nop        | nop                    | bl      ftrace_caller  |
>> | func_body  | func_body              | func_body              |
>>
>> The RA value will be recovered by ftrace_regs_entry, and restored into RA
>> before returning to the regular function prologue. When a function is not
>> being traced, the move t0, ra is not harmful.
>>
>> 1) ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c)
>>     The two functions turn each recorded call site of filtered functions
>>     into a call to ftrace_caller or nops.
>>
>> 2) ftracce_update_ftrace_func (in kernel/ftrace.c)
>>     turns the nops at ftrace_call into a call to a generic entry for
>>     function tracers.
>>
>> 3) ftrace_caller (in kernel/mcount-dyn.S)
>>     The entry where each _mcount call sites calls to once they are
>>     filtered to be traced.
>>
>> Co-developed-by: Jinyang He <hejinyang@loongson.cn>
>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>> Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
>> ---
>>   arch/loongarch/Kconfig                  |   1 +
>>   arch/loongarch/include/asm/ftrace.h     |  16 ++++
>>   arch/loongarch/include/asm/inst.h       |  15 ++++
>>   arch/loongarch/include/asm/unwind.h     |   2 +-
>>   arch/loongarch/kernel/Makefile          |   5 ++
>>   arch/loongarch/kernel/ftrace_dyn.c      | 111 ++++++++++++++++++++++++
>>   arch/loongarch/kernel/inst.c            |  92 ++++++++++++++++++++
>>   arch/loongarch/kernel/mcount-dyn.S      |  89 +++++++++++++++++++
>>   arch/loongarch/kernel/unwind_prologue.c |  35 ++++++--
>>   9 files changed, 360 insertions(+), 6 deletions(-)
>>   create mode 100644 arch/loongarch/kernel/ftrace_dyn.c
>>   create mode 100644 arch/loongarch/kernel/mcount-dyn.S
>>
>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> index e6b1defca1f1..615ce62422b8 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -89,6 +89,7 @@ config LOONGARCH
>>          select HAVE_C_RECORDMCOUNT
>>          select HAVE_DEBUG_STACKOVERFLOW
>>          select HAVE_DMA_CONTIGUOUS
>> +       select HAVE_DYNAMIC_FTRACE
>>          select HAVE_EBPF_JIT
>>          select HAVE_EXIT_THREAD
>>          select HAVE_FAST_GUP
>> diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
>> index 6a3e76234618..76ca58767f4d 100644
>> --- a/arch/loongarch/include/asm/ftrace.h
>> +++ b/arch/loongarch/include/asm/ftrace.h
>> @@ -10,9 +10,25 @@
>>   #define MCOUNT_INSN_SIZE 4             /* sizeof mcount call */
>>
>>   #ifndef __ASSEMBLY__
>> +#ifndef CONFIG_DYNAMIC_FTRACE
>>   extern void _mcount(void);
>>   #define mcount _mcount
>> +#endif
>>
>> +#ifdef CONFIG_DYNAMIC_FTRACE
>> +static inline unsigned long ftrace_call_adjust(unsigned long addr)
>> +{
>> +       return addr;
>> +}
>> +
>> +struct dyn_arch_ftrace {
>> +};
>> +
>> +struct dyn_ftrace;
>> +int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
>> +#define ftrace_init_nop ftrace_init_nop
>> +
>> +#endif /* CONFIG_DYNAMIC_FTRACE */
>>   #endif /* __ASSEMBLY__ */
>>   #endif /* CONFIG_FUNCTION_TRACER */
>>   #endif /* _ASM_LOONGARCH_FTRACE_H */
>> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
>> index a52913787183..0ec775d39ca5 100644
>> --- a/arch/loongarch/include/asm/inst.h
>> +++ b/arch/loongarch/include/asm/inst.h
>> @@ -11,6 +11,9 @@
>>   #define INSN_NOP               0x03400000
>>   #define INSN_BREAK             0x002a0000
>>
>> +#define INSN_NOP 0x03400000
>> +#define INSN_BREAK 0x002a0000
> They are already defined.

Sorry :( , I will resend the next version.

Thanks
-Qing
> 
> Huacai
>> +
>>   #define ADDR_IMMMASK_LU52ID    0xFFF0000000000000
>>   #define ADDR_IMMMASK_LU32ID    0x000FFFFF00000000
>>   #define ADDR_IMMMASK_ADDU16ID  0x00000000FFFF0000
>> @@ -349,6 +352,18 @@ static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
>>                  is_imm12_negative(ip->reg2i12_format.immediate);
>>   }
>>
>> +int larch_insn_read(void *addr, u32 *insnp);
>> +int larch_insn_write(void *addr, u32 insn);
>> +int larch_insn_patch_text(void *addr, u32 insn);
>> +
>> +u32 larch_insn_gen_nop(void);
>> +u32 larch_insn_gen_b(unsigned long pc, unsigned long dest);
>> +u32 larch_insn_gen_bl(unsigned long pc, unsigned long dest);
>> +
>> +u32 larch_insn_gen_or(enum loongarch_gpr rd, enum loongarch_gpr rj,
>> +                       enum loongarch_gpr rk);
>> +u32 larch_insn_gen_move(enum loongarch_gpr rd, enum loongarch_gpr rj);
>> +
>>   u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
>>   u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
>>   u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);
>> diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
>> index 6af4718bdf01..a51eec00efb8 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;
>>          unsigned long sp, pc, ra;
>>   };
>>
>> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
>> index 3f71bce1c7ce..c5e2bfd8247d 100644
>> --- a/arch/loongarch/kernel/Makefile
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -16,8 +16,13 @@ obj-$(CONFIG_EFI)            += efi.o
>>   obj-$(CONFIG_CPU_HAS_FPU)      += fpu.o
>>
>>   ifdef CONFIG_FUNCTION_TRACER
>> +ifndef CONFIG_DYNAMIC_FTRACE
>>   obj-y += mcount.o ftrace.o
>>   CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
>> +else
>> +obj-y += mcount-dyn.o ftrace_dyn.o
>> +CFLAGS_REMOVE_ftrace_dyn.o = $(CC_FLAGS_FTRACE)
>> +endif
>>   CFLAGS_REMOVE_inst.o = $(CC_FLAGS_FTRACE)
>>   CFLAGS_REMOVE_time.o = $(CC_FLAGS_FTRACE)
>>   CFLAGS_REMOVE_perf_event.o = $(CC_FLAGS_FTRACE)
>> diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
>> new file mode 100644
>> index 000000000000..1f8955be8b64
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/ftrace_dyn.c
>> @@ -0,0 +1,111 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Based on arch/arm64/kernel/ftrace.c
>> + *
>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>> + */
>> +
>> +#include <linux/ftrace.h>
>> +#include <linux/uaccess.h>
>> +
>> +#include <asm/inst.h>
>> +
>> +static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
>> +                             bool validate)
>> +{
>> +       u32 replaced;
>> +
>> +       if (validate) {
>> +               if (larch_insn_read((void *)pc, &replaced))
>> +                       return -EFAULT;
>> +
>> +               if (replaced != old)
>> +                       return -EINVAL;
>> +       }
>> +
>> +       if (larch_insn_patch_text((void *)pc, new))
>> +               return -EPERM;
>> +
>> +       return 0;
>> +}
>> +
>> +int ftrace_update_ftrace_func(ftrace_func_t func)
>> +{
>> +       unsigned long pc;
>> +       u32 new;
>> +
>> +       pc = (unsigned long)&ftrace_call;
>> +       new = larch_insn_gen_bl(pc, (unsigned long)func);
>> +
>> +       return ftrace_modify_code(pc, 0, new, false);
>> +}
>> +
>> +/*
>> + * The compiler has inserted 2 NOPs before the regular function prologue.
>> + * T series registers are available and safe because of LoongArch psABI.
>> + *
>> + * At runtime, replace nop with bl to enable ftrace call and replace bl with
>> + * nop to disable ftrace call. The bl requires us to save the original RA value,
>> + * so here it saves RA at t0.
>> + * details are:
>> + *
>> + * | Compiled   |       Disabled         |        Enabled         |
>> + * +------------+------------------------+------------------------+
>> + * | nop        | move     t0, ra        | move     t0, ra        |
>> + * | nop        | nop                    | bl      ftrace_caller  |
>> + * | func_body  | func_body              | func_body              |
>> + *
>> + * The RA value will be recovered by ftrace_regs_entry, and restored into RA
>> + * before returning to the regular function prologue. When a function is not
>> + * being traced, the move t0, ra is not harmful.
>> + */
>> +
>> +int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>> +{
>> +       unsigned long pc;
>> +       u32 old, new;
>> +
>> +       pc = rec->ip;
>> +       old = larch_insn_gen_nop();
>> +       new = larch_insn_gen_move(LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);
>> +
>> +       return ftrace_modify_code(pc, old, new, true);
>> +}
>> +
>> +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>> +{
>> +       unsigned long pc;
>> +       u32 old, new;
>> +
>> +       pc = rec->ip + LOONGARCH_INSN_SIZE;
>> +
>> +       old = larch_insn_gen_nop();
>> +       new = larch_insn_gen_bl(pc, addr);
>> +
>> +       return ftrace_modify_code(pc, old, new, true);
>> +}
>> +
>> +int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>> +                   unsigned long addr)
>> +{
>> +       unsigned long pc;
>> +       u32 old, new;
>> +
>> +       pc = rec->ip + LOONGARCH_INSN_SIZE;
>> +
>> +       new = larch_insn_gen_nop();
>> +       old = larch_insn_gen_bl(pc, addr);
>> +
>> +       return ftrace_modify_code(pc, old, new, true);
>> +}
>> +
>> +void arch_ftrace_update_code(int command)
>> +{
>> +       command |= FTRACE_MAY_SLEEP;
>> +       ftrace_modify_all_code(command);
>> +}
>> +
>> +int __init ftrace_dyn_arch_init(void)
>> +{
>> +       return 0;
>> +}
>> diff --git a/arch/loongarch/kernel/inst.c b/arch/loongarch/kernel/inst.c
>> index b1df0ec34bd1..d62cdf4a9ffb 100644
>> --- a/arch/loongarch/kernel/inst.c
>> +++ b/arch/loongarch/kernel/inst.c
>> @@ -2,8 +2,83 @@
>>   /*
>>    * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>>    */
>> +#include <linux/sizes.h>
>> +#include <linux/uaccess.h>
>> +
>> +#include <asm/cacheflush.h>
>>   #include <asm/inst.h>
>>
>> +static DEFINE_RAW_SPINLOCK(patch_lock);
>> +
>> +int larch_insn_read(void *addr, u32 *insnp)
>> +{
>> +       int ret;
>> +       u32 val;
>> +
>> +       ret = copy_from_kernel_nofault(&val, addr, LOONGARCH_INSN_SIZE);
>> +       if (!ret)
>> +               *insnp = val;
>> +
>> +       return ret;
>> +}
>> +
>> +int larch_insn_write(void *addr, u32 insn)
>> +{
>> +       int ret;
>> +       unsigned long flags = 0;
>> +
>> +       raw_spin_lock_irqsave(&patch_lock, flags);
>> +       ret = copy_to_kernel_nofault(addr, &insn, LOONGARCH_INSN_SIZE);
>> +       raw_spin_unlock_irqrestore(&patch_lock, flags);
>> +
>> +       return ret;
>> +}
>> +
>> +int larch_insn_patch_text(void *addr, u32 insn)
>> +{
>> +       int ret;
>> +       u32 *tp = addr;
>> +
>> +       if ((unsigned long)tp & 3)
>> +               return -EINVAL;
>> +
>> +       ret = larch_insn_write(tp, insn);
>> +       if (!ret)
>> +               flush_icache_range((unsigned long)tp,
>> +                                  (unsigned long)tp + LOONGARCH_INSN_SIZE);
>> +
>> +       return ret;
>> +}
>> +
>> +u32 larch_insn_gen_nop(void)
>> +{
>> +       return INSN_NOP;
>> +}
>> +
>> +u32 larch_insn_gen_bl(unsigned long pc, unsigned long dest)
>> +{
>> +       unsigned int immediate_l, immediate_h;
>> +       union loongarch_instruction insn;
>> +       long offset = dest - pc;
>> +
>> +       if ((offset & 3) || offset < -SZ_128M || offset >= SZ_128M) {
>> +               pr_warn("The generated bl instruction is out of range.\n");
>> +               return INSN_BREAK;
>> +       }
>> +
>> +       offset >>= 2;
>> +
>> +       immediate_l = offset & 0xffff;
>> +       offset >>= 16;
>> +       immediate_h = offset & 0x3ff;
>> +
>> +       insn.reg0i26_format.opcode = bl_op;
>> +       insn.reg0i26_format.immediate_l = immediate_l;
>> +       insn.reg0i26_format.immediate_h = immediate_h;
>> +
>> +       return insn.word;
>> +}
>> +
>>   u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm)
>>   {
>>          union loongarch_instruction insn;
>> @@ -38,3 +113,20 @@ u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned l
>>
>>          return insn.word;
>>   }
>> +
>> +u32 larch_insn_gen_or(enum loongarch_gpr rd, enum loongarch_gpr rj, enum loongarch_gpr rk)
>> +{
>> +       union loongarch_instruction insn;
>> +
>> +       insn.reg3_format.opcode = or_op;
>> +       insn.reg3_format.rd = rd;
>> +       insn.reg3_format.rj = rj;
>> +       insn.reg3_format.rk = rk;
>> +
>> +       return insn.word;
>> +}
>> +
>> +u32 larch_insn_gen_move(enum loongarch_gpr rd, enum loongarch_gpr rj)
>> +{
>> +       return larch_insn_gen_or(rd, rj, 0);
>> +}
>> diff --git a/arch/loongarch/kernel/mcount-dyn.S b/arch/loongarch/kernel/mcount-dyn.S
>> new file mode 100644
>> index 000000000000..205925bc3822
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/mcount-dyn.S
>> @@ -0,0 +1,89 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>> + */
>> +
>> +#include <asm/export.h>
>> +#include <asm/regdef.h>
>> +#include <asm/stackframe.h>
>> +#include <asm/ftrace.h>
>> +
>> +       .text
>> +/*
>> + * Due to -fpatchable-function-entry=2: the compiler inserted 2 NOPs before the
>> + * regular C function prologue. When PC arrived here, the last 2 instructions
>> + * as follows,
>> + *     move            t0, ra
>> + *     bl              callsite (for modules, callsite is a tramplione)
>> + *
>> + * modules tramplione as follows,
>> + *     lu12i.w         t1, callsite[31:12]
>> + *     lu32i.d         t1, callsite[51:32]
>> + *     lu52i.d         t1, t1, callsite[63:52]
>> + *     jirl            zero, t1, callsite[11:0] >> 2
>> + *
>> + * See arch/loongarch/kernel/ftrace_dyn.c for details. Here, pay attention to
>> + * that the T series regs are available and safe because each C functions
>> + * follows the LoongArch psABI well.
>> + */
>> +
>> +       .macro  ftrace_regs_entry
>> +       PTR_ADDI sp, sp, -PT_SIZE
>> +       /* Save trace function ra at PT_ERA */
>> +       PTR_S   ra, sp, PT_ERA
>> +       /* Save parent ra at PT_R1(RA) */
>> +       PTR_S   t0, sp, PT_R1
>> +       PTR_S   a0, sp, PT_R4
>> +       PTR_S   a1, sp, PT_R5
>> +       PTR_S   a2, sp, PT_R6
>> +       PTR_S   a3, sp, PT_R7
>> +       PTR_S   a4, sp, PT_R8
>> +       PTR_S   a5, sp, PT_R9
>> +       PTR_S   a6, sp, PT_R10
>> +       PTR_S   a7, sp, PT_R11
>> +       PTR_S   fp, sp, PT_R22
>> +
>> +       PTR_ADDI t8, sp, PT_SIZE
>> +       PTR_S   t8, sp, PT_R3
>> +
>> +       .endm
>> +
>> +SYM_CODE_START(ftrace_caller)
>> +       ftrace_regs_entry
>> +       b       ftrace_common
>> +SYM_CODE_END(ftrace_caller)
>> +
>> +SYM_CODE_START(ftrace_common)
>> +       PTR_ADDI        a0, ra, -8      /* arg0: ip */
>> +       move            a1, t0          /* arg1: parent_ip */
>> +       la.pcrel        t1, function_trace_op
>> +       PTR_L           a2, t1, 0       /* arg2: op */
>> +       move            a3, sp          /* arg3: regs */
>> +       .globl ftrace_call
>> +ftrace_call:
>> +       bl              ftrace_stub
>> +/*
>> + * As we didn't use S series regs in this assmembly code and all calls
>> + * are C function which will save S series regs by themselves, there is
>> + * no need to restore S series regs. The T series is available and safe
>> + * at the callsite, so there is no need to restore the T series regs.
>> + */
>> +ftrace_common_return:
>> +       PTR_L   a0, sp, PT_R4
>> +       PTR_L   a1, sp, PT_R5
>> +       PTR_L   a2, sp, PT_R6
>> +       PTR_L   a3, sp, PT_R7
>> +       PTR_L   a4, sp, PT_R8
>> +       PTR_L   a5, sp, PT_R9
>> +       PTR_L   a6, sp, PT_R10
>> +       PTR_L   a7, sp, PT_R11
>> +       PTR_L   fp, sp, PT_R22
>> +       PTR_L   ra, sp, PT_R1
>> +       PTR_L   t0, sp, PT_ERA
>> +       PTR_ADDI sp, sp, PT_SIZE
>> +       jr      t0
>> +SYM_CODE_END(ftrace_common)
>> +
>> +SYM_FUNC_START(ftrace_stub)
>> +       jr      ra
>> +SYM_FUNC_END(ftrace_stub)
>> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
>> index b206d9159205..c5df4ae73e0d 100644
>> --- a/arch/loongarch/kernel/unwind_prologue.c
>> +++ b/arch/loongarch/kernel/unwind_prologue.c
>> @@ -13,9 +13,7 @@ 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);
>> @@ -39,16 +37,41 @@ static bool unwind_by_guess(struct unwind_state *state)
>>          return false;
>>   }
>>
>> +static inline void unwind_state_fixup(struct unwind_state *state)
>> +{
>> +#ifdef CONFIG_DYNAMIC_FTRACE
>> +       static unsigned long ftrace_case = (unsigned long)ftrace_call + 4;
>> +
>> +       if (state->pc == ftrace_case)
>> +               state->is_ftrace = true;
>> +#endif
>> +}
>> +
>>   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;
>>
>> @@ -94,7 +117,7 @@ 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;
>> @@ -103,7 +126,9 @@ 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,
>> --
>> 2.36.0
>>
>>