diff mbox series

[-next,V7,3/7] riscv: ftrace: Reduce the detour code size to half

Message ID 20230112090603.1295340-4-guoren@kernel.org (mailing list archive)
State Accepted
Commit 6724a76cff85ee271bbbff42ac527e4643b2ec52
Delegated to: Palmer Dabbelt
Headers show
Series riscv: Optimize function trace | expand

Checks

Context Check Description
conchuod/build_warn_rv64 success Errors and warnings before: 2054 this patch: 2054
conchuod/patch_count success Link
conchuod/cover_letter success Series has a cover letter
conchuod/tree_selection success Guessed tree name to be fixes
conchuod/fixes_present success Fixes tag present in non-next series
conchuod/maintainers_pattern success MAINTAINERS pattern errors before the patch: 13 and now 13
conchuod/verify_signedoff success Signed-off-by tag matches author and committer
conchuod/kdoc success Errors and warnings before: 0 this patch: 0
conchuod/module_param success Was 0 now: 0
conchuod/build_rv64_gcc_allmodconfig success Errors and warnings before: 2014 this patch: 0
conchuod/alphanumeric_selects success Out of order selects before the patch: 57 and now 57
conchuod/build_rv32_defconfig success Build OK
conchuod/dtb_warn_rv64 success Errors and warnings before: 4 this patch: 4
conchuod/header_inline success No static functions without inline keyword in header files
conchuod/checkpatch warning CHECK: Macro argument 'callee' may be better as '(callee)' to avoid precedence issues CHECK: Macro argument 'offset' may be better as '(offset)' to avoid precedence issues CHECK: No space is necessary after a cast
conchuod/source_inline success Was 0 now: 0
conchuod/build_rv64_nommu_k210_defconfig success Build OK
conchuod/verify_fixes success No Fixes tag
conchuod/build_rv64_nommu_virt_defconfig success Build OK

Commit Message

Guo Ren Jan. 12, 2023, 9:05 a.m. UTC 
From: Guo Ren <guoren@linux.alibaba.com>

Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.

Before the patch:
<func_prolog>:
 0: REG_S  ra, -SZREG(sp)
 4: auipc  ra, ?
 8: jalr   ?(ra)
12: REG_L  ra, -SZREG(sp)
 (func_boddy)

After the patch:
<func_prolog>:
 0: auipc  t0, ?
 4: jalr   t0, ?(t0)
 (func_boddy)

This patch not just reduces the size of detour code, but also fixes an
important issue:

An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.

In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.

This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.

Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
---
 arch/riscv/Makefile             |  4 +-
 arch/riscv/include/asm/ftrace.h | 50 +++++++++++++++++++------
 arch/riscv/kernel/ftrace.c      | 65 ++++++++++-----------------------
 arch/riscv/kernel/mcount-dyn.S  | 42 ++++++++-------------
 4 files changed, 75 insertions(+), 86 deletions(-)

Comments

Evgenii Shatokhin Jan. 16, 2023, 2:11 p.m. UTC | #1 
Hi,

On 12.01.2023 12:05, guoren@kernel.org wrote:
> From: Guo Ren <guoren@linux.alibaba.com>
> 
> Use a temporary register to reduce the size of detour code from 16 bytes to
> 8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
> Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
> 
> Before the patch:
> <func_prolog>:
>   0: REG_S  ra, -SZREG(sp)
>   4: auipc  ra, ?
>   8: jalr   ?(ra)
> 12: REG_L  ra, -SZREG(sp)
>   (func_boddy)
> 
> After the patch:
> <func_prolog>:
>   0: auipc  t0, ?
>   4: jalr   t0, ?(t0)
>   (func_boddy)
> 
> This patch not just reduces the size of detour code, but also fixes an
> important issue:
> 
> An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
> actually change the instruction pointer, e.g. to "replace" the given
> kernel function with a new one, which is needed for livepatching, etc.
> 
> In this case, the trampoline (ftrace_regs_caller) would not return to
> <func_prolog+12> but would rather jump to the new function. So, "REG_L
> ra, -SZREG(sp)" would not run and the original return address would not
> be restored. The kernel is likely to hang or crash as a result.
> 
> This can be easily demonstrated if one tries to "replace", say,
> cmdline_proc_show() with a new function with the same signature using
> instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
> callback.
> 
> Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
> Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
> Co-developed-by: Song Shuai <suagrfillet@gmail.com>
> Signed-off-by: Song Shuai <suagrfillet@gmail.com>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> Cc: Evgenii Shatokhin <e.shatokhin@yadro.com>
> ---
>   arch/riscv/Makefile             |  4 +-
>   arch/riscv/include/asm/ftrace.h | 50 +++++++++++++++++++------
>   arch/riscv/kernel/ftrace.c      | 65 ++++++++++-----------------------
>   arch/riscv/kernel/mcount-dyn.S  | 42 ++++++++-------------
>   4 files changed, 75 insertions(+), 86 deletions(-)
> 
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index ea5a91da6897..3c9aaf67ed79 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -12,9 +12,9 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>          LDFLAGS_vmlinux := --no-relax
>          KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
>   ifeq ($(CONFIG_RISCV_ISA_C),y)
> -       CC_FLAGS_FTRACE := -fpatchable-function-entry=8
> -else
>          CC_FLAGS_FTRACE := -fpatchable-function-entry=4
> +else
> +       CC_FLAGS_FTRACE := -fpatchable-function-entry=2
>   endif
>   endif
> 
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 04dad3380041..9e73922e1e2e 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -42,6 +42,14 @@ struct dyn_arch_ftrace {
>    * 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to
>    *          return address (original pc + 4)
>    *
> + *<ftrace enable>:
> + * 0: auipc  t0/ra, 0x?
> + * 4: jalr   t0/ra, ?(t0/ra)
> + *
> + *<ftrace disable>:
> + * 0: nop
> + * 4: nop
> + *
>    * Dynamic ftrace generates probes to call sites, so we must deal with
>    * both auipc and jalr at the same time.
>    */
> @@ -52,25 +60,43 @@ struct dyn_arch_ftrace {
>   #define AUIPC_OFFSET_MASK      (0xfffff000)
>   #define AUIPC_PAD              (0x00001000)
>   #define JALR_SHIFT             20
> -#define JALR_BASIC             (0x000080e7)
> -#define AUIPC_BASIC            (0x00000097)
> +#define JALR_RA                        (0x000080e7)
> +#define AUIPC_RA               (0x00000097)
> +#define JALR_T0                        (0x000282e7)
> +#define AUIPC_T0               (0x00000297)
>   #define NOP4                   (0x00000013)
> 
> -#define make_call(caller, callee, call)                                        \
> +#define to_jalr_t0(offset)                                             \
> +       (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0)
> +
> +#define to_auipc_t0(offset)                                            \
> +       ((offset & JALR_SIGN_MASK) ?                                    \
> +       (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_T0) :       \
> +       ((offset & AUIPC_OFFSET_MASK) | AUIPC_T0))
> +
> +#define make_call_t0(caller, callee, call)                             \
>   do {                                                                   \
> -       call[0] = to_auipc_insn((unsigned int)((unsigned long)callee -  \
> -                               (unsigned long)caller));                \
> -       call[1] = to_jalr_insn((unsigned int)((unsigned long)callee -   \
> -                              (unsigned long)caller));                 \
> +       unsigned int offset =                                           \
> +               (unsigned long) callee - (unsigned long) caller;        \
> +       call[0] = to_auipc_t0(offset);                                  \
> +       call[1] = to_jalr_t0(offset);                                   \
>   } while (0)
> 
> -#define to_jalr_insn(offset)                                           \
> -       (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_BASIC)
> +#define to_jalr_ra(offset)                                             \
> +       (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_RA)
> 
> -#define to_auipc_insn(offset)                                          \
> +#define to_auipc_ra(offset)                                            \
>          ((offset & JALR_SIGN_MASK) ?                                    \
> -       (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_BASIC) :    \
> -       ((offset & AUIPC_OFFSET_MASK) | AUIPC_BASIC))
> +       (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_RA) :       \
> +       ((offset & AUIPC_OFFSET_MASK) | AUIPC_RA))
> +
> +#define make_call_ra(caller, callee, call)                             \
> +do {                                                                   \
> +       unsigned int offset =                                           \
> +               (unsigned long) callee - (unsigned long) caller;        \
> +       call[0] = to_auipc_ra(offset);                                  \
> +       call[1] = to_jalr_ra(offset);                                   \
> +} while (0)
> 
>   /*
>    * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index 2086f6585773..5bff37af4770 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -55,12 +55,15 @@ static int ftrace_check_current_call(unsigned long hook_pos,
>   }
> 
>   static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
> -                               bool enable)
> +                               bool enable, bool ra)
>   {
>          unsigned int call[2];
>          unsigned int nops[2] = {NOP4, NOP4};
> 
> -       make_call(hook_pos, target, call);
> +       if (ra)
> +               make_call_ra(hook_pos, target, call);
> +       else
> +               make_call_t0(hook_pos, target, call);
> 
>          /* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
>          if (patch_text_nosync
> @@ -70,42 +73,13 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
>          return 0;
>   }
> 
> -/*
> - * Put 5 instructions with 16 bytes at the front of function within
> - * patchable function entry nops' area.
> - *
> - * 0: REG_S  ra, -SZREG(sp)
> - * 1: auipc  ra, 0x?
> - * 2: jalr   -?(ra)
> - * 3: REG_L  ra, -SZREG(sp)
> - *
> - * So the opcodes is:
> - * 0: 0xfe113c23 (sd)/0xfe112e23 (sw)
> - * 1: 0x???????? -> auipc
> - * 2: 0x???????? -> jalr
> - * 3: 0xff813083 (ld)/0xffc12083 (lw)
> - */
> -#if __riscv_xlen == 64
> -#define INSN0  0xfe113c23
> -#define INSN3  0xff813083
> -#elif __riscv_xlen == 32
> -#define INSN0  0xfe112e23
> -#define INSN3  0xffc12083
> -#endif
> -
> -#define FUNC_ENTRY_SIZE        16
> -#define FUNC_ENTRY_JMP 4
> -
>   int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>   {
> -       unsigned int call[4] = {INSN0, 0, 0, INSN3};
> -       unsigned long target = addr;
> -       unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
> +       unsigned int call[2];
> 
> -       call[1] = to_auipc_insn((unsigned int)(target - caller));
> -       call[2] = to_jalr_insn((unsigned int)(target - caller));
> +       make_call_t0(rec->ip, addr, call);
> 
> -       if (patch_text_nosync((void *)rec->ip, call, FUNC_ENTRY_SIZE))
> +       if (patch_text_nosync((void *)rec->ip, call, MCOUNT_INSN_SIZE))
>                  return -EPERM;
> 
>          return 0;
> @@ -114,15 +88,14 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>   int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>                      unsigned long addr)
>   {
> -       unsigned int nops[4] = {NOP4, NOP4, NOP4, NOP4};
> +       unsigned int nops[2] = {NOP4, NOP4};
> 
> -       if (patch_text_nosync((void *)rec->ip, nops, FUNC_ENTRY_SIZE))
> +       if (patch_text_nosync((void *)rec->ip, nops, MCOUNT_INSN_SIZE))
>                  return -EPERM;
> 
>          return 0;
>   }
> 
> -
>   /*
>    * This is called early on, and isn't wrapped by
>    * ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold
> @@ -144,10 +117,10 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
>   int ftrace_update_ftrace_func(ftrace_func_t func)
>   {
>          int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
> -                                      (unsigned long)func, true);
> +                                      (unsigned long)func, true, true);
>          if (!ret) {
>                  ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call,
> -                                          (unsigned long)func, true);
> +                                          (unsigned long)func, true, true);
>          }
> 
>          return ret;
> @@ -159,16 +132,16 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
>                         unsigned long addr)
>   {
>          unsigned int call[2];
> -       unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
> +       unsigned long caller = rec->ip;
>          int ret;
> 
> -       make_call(caller, old_addr, call);
> +       make_call_t0(caller, old_addr, call);
>          ret = ftrace_check_current_call(caller, call);
> 
>          if (ret)
>                  return ret;
> 
> -       return __ftrace_modify_call(caller, addr, true);
> +       return __ftrace_modify_call(caller, addr, true, false);
>   }
>   #endif
> 
> @@ -203,12 +176,12 @@ int ftrace_enable_ftrace_graph_caller(void)
>          int ret;
> 
>          ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
> -                                   (unsigned long)&prepare_ftrace_return, true);
> +                                   (unsigned long)&prepare_ftrace_return, true, true);
>          if (ret)
>                  return ret;
> 
>          return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
> -                                   (unsigned long)&prepare_ftrace_return, true);
> +                                   (unsigned long)&prepare_ftrace_return, true, true);
>   }
> 
>   int ftrace_disable_ftrace_graph_caller(void)
> @@ -216,12 +189,12 @@ int ftrace_disable_ftrace_graph_caller(void)
>          int ret;
> 
>          ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
> -                                   (unsigned long)&prepare_ftrace_return, false);
> +                                   (unsigned long)&prepare_ftrace_return, false, true);
>          if (ret)
>                  return ret;
> 
>          return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
> -                                   (unsigned long)&prepare_ftrace_return, false);
> +                                   (unsigned long)&prepare_ftrace_return, false, true);
>   }
>   #endif /* CONFIG_DYNAMIC_FTRACE */
>   #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
> diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> index d171eca623b6..125de818d1ba 100644
> --- a/arch/riscv/kernel/mcount-dyn.S
> +++ b/arch/riscv/kernel/mcount-dyn.S
> @@ -13,8 +13,8 @@
> 
>          .text
> 
> -#define FENTRY_RA_OFFSET       12
> -#define ABI_SIZE_ON_STACK      72
> +#define FENTRY_RA_OFFSET       8
> +#define ABI_SIZE_ON_STACK      80
>   #define ABI_A0                 0
>   #define ABI_A1                 8
>   #define ABI_A2                 16
> @@ -23,10 +23,10 @@
>   #define ABI_A5                 40
>   #define ABI_A6                 48
>   #define ABI_A7                 56
> -#define ABI_RA                 64
> +#define ABI_T0                 64
> +#define ABI_RA                 72
> 
>          .macro SAVE_ABI
> -       addi    sp, sp, -SZREG
>          addi    sp, sp, -ABI_SIZE_ON_STACK
> 
>          REG_S   a0, ABI_A0(sp)
> @@ -37,6 +37,7 @@
>          REG_S   a5, ABI_A5(sp)
>          REG_S   a6, ABI_A6(sp)
>          REG_S   a7, ABI_A7(sp)
> +       REG_S   t0, ABI_T0(sp)
>          REG_S   ra, ABI_RA(sp)
>          .endm
> 
> @@ -49,24 +50,18 @@
>          REG_L   a5, ABI_A5(sp)
>          REG_L   a6, ABI_A6(sp)
>          REG_L   a7, ABI_A7(sp)
> +       REG_L   t0, ABI_T0(sp)
>          REG_L   ra, ABI_RA(sp)
> 
>          addi    sp, sp, ABI_SIZE_ON_STACK
> -       addi    sp, sp, SZREG
>          .endm
> 
>   #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>          .macro SAVE_ALL
> -       addi    sp, sp, -SZREG
>          addi    sp, sp, -PT_SIZE_ON_STACK
> 
> -       REG_S x1,  PT_EPC(sp)
> -       addi    sp, sp, PT_SIZE_ON_STACK
> -       REG_L x1,  (sp)
> -       addi    sp, sp, -PT_SIZE_ON_STACK
> +       REG_S t0,  PT_EPC(sp)
>          REG_S x1,  PT_RA(sp)
> -       REG_L x1,  PT_EPC(sp)
> -
>          REG_S x2,  PT_SP(sp)
>          REG_S x3,  PT_GP(sp)
>          REG_S x4,  PT_TP(sp)
> @@ -100,15 +95,11 @@
>          .endm
> 
>          .macro RESTORE_ALL
> +       REG_L t0,  PT_EPC(sp)
>          REG_L x1,  PT_RA(sp)
> -       addi    sp, sp, PT_SIZE_ON_STACK
> -       REG_S x1,  (sp)
> -       addi    sp, sp, -PT_SIZE_ON_STACK
> -       REG_L x1,  PT_EPC(sp)
>          REG_L x2,  PT_SP(sp)
>          REG_L x3,  PT_GP(sp)
>          REG_L x4,  PT_TP(sp)
> -       REG_L x5,  PT_T0(sp)
>          REG_L x6,  PT_T1(sp)
>          REG_L x7,  PT_T2(sp)
>          REG_L x8,  PT_S0(sp)
> @@ -137,17 +128,16 @@
>          REG_L x31, PT_T6(sp)
> 
>          addi    sp, sp, PT_SIZE_ON_STACK
> -       addi    sp, sp, SZREG
>          .endm
>   #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> 
>   ENTRY(ftrace_caller)
>          SAVE_ABI
> 
> -       addi    a0, ra, -FENTRY_RA_OFFSET
> +       addi    a0, t0, -FENTRY_RA_OFFSET
>          la      a1, function_trace_op
>          REG_L   a2, 0(a1)
> -       REG_L   a1, ABI_SIZE_ON_STACK(sp)
> +       mv      a1, ra
>          mv      a3, sp
> 
>   ftrace_call:
> @@ -155,8 +145,8 @@ ftrace_call:
>          call    ftrace_stub
> 
>   #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> -       addi    a0, sp, ABI_SIZE_ON_STACK
> -       REG_L   a1, ABI_RA(sp)
> +       addi    a0, sp, ABI_RA
> +       REG_L   a1, ABI_T0(sp)
>          addi    a1, a1, -FENTRY_RA_OFFSET
>   #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
>          mv      a2, s0
> @@ -166,17 +156,17 @@ ftrace_graph_call:
>          call    ftrace_stub
>   #endif
>          RESTORE_ABI
> -       ret
> +       jr t0
>   ENDPROC(ftrace_caller)
> 
>   #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>   ENTRY(ftrace_regs_caller)
>          SAVE_ALL
> 
> -       addi    a0, ra, -FENTRY_RA_OFFSET
> +       addi    a0, t0, -FENTRY_RA_OFFSET
>          la      a1, function_trace_op
>          REG_L   a2, 0(a1)
> -       REG_L   a1, PT_SIZE_ON_STACK(sp)
> +       mv      a1, ra
>          mv      a3, sp
> 
>   ftrace_regs_call:
> @@ -196,6 +186,6 @@ ftrace_graph_regs_call:
>   #endif
> 
>          RESTORE_ALL
> -       ret
> +       jr t0
>   ENDPROC(ftrace_regs_caller)
>   #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> --
> 2.36.1
> 
> 

Looks good to me.

I also re-checked if "replacement" of cmdline_proc_show() with a custom 
function via Ftrace works in this case - it does. Rollback to the 
original cmdline_proc_show() seems to work OK too.

Reviewed-by: Evgenii Shatokhin <e.shatokhin@yadro.com>

Regards,
Evgenii
diff mbox series

Patch

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index ea5a91da6897..3c9aaf67ed79 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -12,9 +12,9 @@  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
 	LDFLAGS_vmlinux := --no-relax
 	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
 ifeq ($(CONFIG_RISCV_ISA_C),y)
-	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
-else
 	CC_FLAGS_FTRACE := -fpatchable-function-entry=4
+else
+	CC_FLAGS_FTRACE := -fpatchable-function-entry=2
 endif
 endif
 
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 04dad3380041..9e73922e1e2e 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -42,6 +42,14 @@  struct dyn_arch_ftrace {
  * 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to
  *          return address (original pc + 4)
  *
+ *<ftrace enable>:
+ * 0: auipc  t0/ra, 0x?
+ * 4: jalr   t0/ra, ?(t0/ra)
+ *
+ *<ftrace disable>:
+ * 0: nop
+ * 4: nop
+ *
  * Dynamic ftrace generates probes to call sites, so we must deal with
  * both auipc and jalr at the same time.
  */
@@ -52,25 +60,43 @@  struct dyn_arch_ftrace {
 #define AUIPC_OFFSET_MASK	(0xfffff000)
 #define AUIPC_PAD		(0x00001000)
 #define JALR_SHIFT		20
-#define JALR_BASIC		(0x000080e7)
-#define AUIPC_BASIC		(0x00000097)
+#define JALR_RA			(0x000080e7)
+#define AUIPC_RA		(0x00000097)
+#define JALR_T0			(0x000282e7)
+#define AUIPC_T0		(0x00000297)
 #define NOP4			(0x00000013)
 
-#define make_call(caller, callee, call)					\
+#define to_jalr_t0(offset)						\
+	(((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0)
+
+#define to_auipc_t0(offset)						\
+	((offset & JALR_SIGN_MASK) ?					\
+	(((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_T0) :	\
+	((offset & AUIPC_OFFSET_MASK) | AUIPC_T0))
+
+#define make_call_t0(caller, callee, call)				\
 do {									\
-	call[0] = to_auipc_insn((unsigned int)((unsigned long)callee -	\
-				(unsigned long)caller));		\
-	call[1] = to_jalr_insn((unsigned int)((unsigned long)callee -	\
-			       (unsigned long)caller));			\
+	unsigned int offset =						\
+		(unsigned long) callee - (unsigned long) caller;	\
+	call[0] = to_auipc_t0(offset);					\
+	call[1] = to_jalr_t0(offset);					\
 } while (0)
 
-#define to_jalr_insn(offset)						\
-	(((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_BASIC)
+#define to_jalr_ra(offset)						\
+	(((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_RA)
 
-#define to_auipc_insn(offset)						\
+#define to_auipc_ra(offset)						\
 	((offset & JALR_SIGN_MASK) ?					\
-	(((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_BASIC) :	\
-	((offset & AUIPC_OFFSET_MASK) | AUIPC_BASIC))
+	(((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_RA) :	\
+	((offset & AUIPC_OFFSET_MASK) | AUIPC_RA))
+
+#define make_call_ra(caller, callee, call)				\
+do {									\
+	unsigned int offset =						\
+		(unsigned long) callee - (unsigned long) caller;	\
+	call[0] = to_auipc_ra(offset);					\
+	call[1] = to_jalr_ra(offset);					\
+} while (0)
 
 /*
  * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 2086f6585773..5bff37af4770 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -55,12 +55,15 @@  static int ftrace_check_current_call(unsigned long hook_pos,
 }
 
 static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
-				bool enable)
+				bool enable, bool ra)
 {
 	unsigned int call[2];
 	unsigned int nops[2] = {NOP4, NOP4};
 
-	make_call(hook_pos, target, call);
+	if (ra)
+		make_call_ra(hook_pos, target, call);
+	else
+		make_call_t0(hook_pos, target, call);
 
 	/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
 	if (patch_text_nosync
@@ -70,42 +73,13 @@  static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
 	return 0;
 }
 
-/*
- * Put 5 instructions with 16 bytes at the front of function within
- * patchable function entry nops' area.
- *
- * 0: REG_S  ra, -SZREG(sp)
- * 1: auipc  ra, 0x?
- * 2: jalr   -?(ra)
- * 3: REG_L  ra, -SZREG(sp)
- *
- * So the opcodes is:
- * 0: 0xfe113c23 (sd)/0xfe112e23 (sw)
- * 1: 0x???????? -> auipc
- * 2: 0x???????? -> jalr
- * 3: 0xff813083 (ld)/0xffc12083 (lw)
- */
-#if __riscv_xlen == 64
-#define INSN0	0xfe113c23
-#define INSN3	0xff813083
-#elif __riscv_xlen == 32
-#define INSN0	0xfe112e23
-#define INSN3	0xffc12083
-#endif
-
-#define FUNC_ENTRY_SIZE	16
-#define FUNC_ENTRY_JMP	4
-
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
-	unsigned int call[4] = {INSN0, 0, 0, INSN3};
-	unsigned long target = addr;
-	unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
+	unsigned int call[2];
 
-	call[1] = to_auipc_insn((unsigned int)(target - caller));
-	call[2] = to_jalr_insn((unsigned int)(target - caller));
+	make_call_t0(rec->ip, addr, call);
 
-	if (patch_text_nosync((void *)rec->ip, call, FUNC_ENTRY_SIZE))
+	if (patch_text_nosync((void *)rec->ip, call, MCOUNT_INSN_SIZE))
 		return -EPERM;
 
 	return 0;
@@ -114,15 +88,14 @@  int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 		    unsigned long addr)
 {
-	unsigned int nops[4] = {NOP4, NOP4, NOP4, NOP4};
+	unsigned int nops[2] = {NOP4, NOP4};
 
-	if (patch_text_nosync((void *)rec->ip, nops, FUNC_ENTRY_SIZE))
+	if (patch_text_nosync((void *)rec->ip, nops, MCOUNT_INSN_SIZE))
 		return -EPERM;
 
 	return 0;
 }
 
-
 /*
  * This is called early on, and isn't wrapped by
  * ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold
@@ -144,10 +117,10 @@  int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
 	int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
-				       (unsigned long)func, true);
+				       (unsigned long)func, true, true);
 	if (!ret) {
 		ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call,
-					   (unsigned long)func, true);
+					   (unsigned long)func, true, true);
 	}
 
 	return ret;
@@ -159,16 +132,16 @@  int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 		       unsigned long addr)
 {
 	unsigned int call[2];
-	unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
+	unsigned long caller = rec->ip;
 	int ret;
 
-	make_call(caller, old_addr, call);
+	make_call_t0(caller, old_addr, call);
 	ret = ftrace_check_current_call(caller, call);
 
 	if (ret)
 		return ret;
 
-	return __ftrace_modify_call(caller, addr, true);
+	return __ftrace_modify_call(caller, addr, true, false);
 }
 #endif
 
@@ -203,12 +176,12 @@  int ftrace_enable_ftrace_graph_caller(void)
 	int ret;
 
 	ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
-				    (unsigned long)&prepare_ftrace_return, true);
+				    (unsigned long)&prepare_ftrace_return, true, true);
 	if (ret)
 		return ret;
 
 	return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
-				    (unsigned long)&prepare_ftrace_return, true);
+				    (unsigned long)&prepare_ftrace_return, true, true);
 }
 
 int ftrace_disable_ftrace_graph_caller(void)
@@ -216,12 +189,12 @@  int ftrace_disable_ftrace_graph_caller(void)
 	int ret;
 
 	ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
-				    (unsigned long)&prepare_ftrace_return, false);
+				    (unsigned long)&prepare_ftrace_return, false, true);
 	if (ret)
 		return ret;
 
 	return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
-				    (unsigned long)&prepare_ftrace_return, false);
+				    (unsigned long)&prepare_ftrace_return, false, true);
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index d171eca623b6..125de818d1ba 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -13,8 +13,8 @@ 
 
 	.text
 
-#define FENTRY_RA_OFFSET	12
-#define ABI_SIZE_ON_STACK	72
+#define FENTRY_RA_OFFSET	8
+#define ABI_SIZE_ON_STACK	80
 #define ABI_A0			0
 #define ABI_A1			8
 #define ABI_A2			16
@@ -23,10 +23,10 @@ 
 #define ABI_A5			40
 #define ABI_A6			48
 #define ABI_A7			56
-#define ABI_RA			64
+#define ABI_T0			64
+#define ABI_RA			72
 
 	.macro SAVE_ABI
-	addi	sp, sp, -SZREG
 	addi	sp, sp, -ABI_SIZE_ON_STACK
 
 	REG_S	a0, ABI_A0(sp)
@@ -37,6 +37,7 @@ 
 	REG_S	a5, ABI_A5(sp)
 	REG_S	a6, ABI_A6(sp)
 	REG_S	a7, ABI_A7(sp)
+	REG_S	t0, ABI_T0(sp)
 	REG_S	ra, ABI_RA(sp)
 	.endm
 
@@ -49,24 +50,18 @@ 
 	REG_L	a5, ABI_A5(sp)
 	REG_L	a6, ABI_A6(sp)
 	REG_L	a7, ABI_A7(sp)
+	REG_L	t0, ABI_T0(sp)
 	REG_L	ra, ABI_RA(sp)
 
 	addi	sp, sp, ABI_SIZE_ON_STACK
-	addi	sp, sp, SZREG
 	.endm
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 	.macro SAVE_ALL
-	addi	sp, sp, -SZREG
 	addi	sp, sp, -PT_SIZE_ON_STACK
 
-	REG_S x1,  PT_EPC(sp)
-	addi	sp, sp, PT_SIZE_ON_STACK
-	REG_L x1,  (sp)
-	addi	sp, sp, -PT_SIZE_ON_STACK
+	REG_S t0,  PT_EPC(sp)
 	REG_S x1,  PT_RA(sp)
-	REG_L x1,  PT_EPC(sp)
-
 	REG_S x2,  PT_SP(sp)
 	REG_S x3,  PT_GP(sp)
 	REG_S x4,  PT_TP(sp)
@@ -100,15 +95,11 @@ 
 	.endm
 
 	.macro RESTORE_ALL
+	REG_L t0,  PT_EPC(sp)
 	REG_L x1,  PT_RA(sp)
-	addi	sp, sp, PT_SIZE_ON_STACK
-	REG_S x1,  (sp)
-	addi	sp, sp, -PT_SIZE_ON_STACK
-	REG_L x1,  PT_EPC(sp)
 	REG_L x2,  PT_SP(sp)
 	REG_L x3,  PT_GP(sp)
 	REG_L x4,  PT_TP(sp)
-	REG_L x5,  PT_T0(sp)
 	REG_L x6,  PT_T1(sp)
 	REG_L x7,  PT_T2(sp)
 	REG_L x8,  PT_S0(sp)
@@ -137,17 +128,16 @@ 
 	REG_L x31, PT_T6(sp)
 
 	addi	sp, sp, PT_SIZE_ON_STACK
-	addi	sp, sp, SZREG
 	.endm
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 
 ENTRY(ftrace_caller)
 	SAVE_ABI
 
-	addi	a0, ra, -FENTRY_RA_OFFSET
+	addi	a0, t0, -FENTRY_RA_OFFSET
 	la	a1, function_trace_op
 	REG_L	a2, 0(a1)
-	REG_L	a1, ABI_SIZE_ON_STACK(sp)
+	mv	a1, ra
 	mv	a3, sp
 
 ftrace_call:
@@ -155,8 +145,8 @@  ftrace_call:
 	call	ftrace_stub
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	addi	a0, sp, ABI_SIZE_ON_STACK
-	REG_L	a1, ABI_RA(sp)
+	addi	a0, sp, ABI_RA
+	REG_L	a1, ABI_T0(sp)
 	addi	a1, a1, -FENTRY_RA_OFFSET
 #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 	mv	a2, s0
@@ -166,17 +156,17 @@  ftrace_graph_call:
 	call	ftrace_stub
 #endif
 	RESTORE_ABI
-	ret
+	jr t0
 ENDPROC(ftrace_caller)
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 ENTRY(ftrace_regs_caller)
 	SAVE_ALL
 
-	addi	a0, ra, -FENTRY_RA_OFFSET
+	addi	a0, t0, -FENTRY_RA_OFFSET
 	la	a1, function_trace_op
 	REG_L	a2, 0(a1)
-	REG_L	a1, PT_SIZE_ON_STACK(sp)
+	mv	a1, ra
 	mv	a3, sp
 
 ftrace_regs_call:
@@ -196,6 +186,6 @@  ftrace_graph_regs_call:
 #endif
 
 	RESTORE_ALL
-	ret
+	jr t0
 ENDPROC(ftrace_regs_caller)
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */