diff options
| author | Guo Ren <guoren@linux.alibaba.com> | 2020-12-17 16:01:41 +0000 |
|---|---|---|
| committer | Palmer Dabbelt <palmerdabbelt@google.com> | 2021-01-14 15:09:05 -0800 |
| commit | afc76b8b80112189b6f11e67e19cf58301944814 (patch) | |
| tree | 034c48f5730615893aa5d89f8c8e2327e2cb8585 /arch/riscv/Makefile | |
| parent | 5ad84adf5456313e285734102367c861c436c5ed (diff) | |
riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT
This patch changes the current detour mechanism of dynamic ftrace
which has been discussed during LPC 2020 RISCV-MC [1].
Before the patch, we used mcount for detour:
<funca>:
addi sp,sp,-16
sd ra,8(sp)
sd s0,0(sp)
addi s0,sp,16
mv a5,ra
mv a0,a5
auipc ra,0x0 -> nop
jalr -296(ra) <_mcount@plt> ->nop
...
After the patch, we use nop call site area for detour:
<funca>:
nop -> REG_S ra, -SZREG(sp)
nop -> auipc ra, 0x?
nop -> jalr ?(ra)
nop -> REG_L ra, -SZREG(sp)
...
The mcount mechanism is mixed with gcc function prologue which is
not very clear. The patchable function entry just put 16 bytes nop
before the front of the function prologue which could be filled
with a separated detour mechanism.
[1] https://www.linuxplumbersconf.org/event/7/contributions/807/
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Diffstat (limited to 'arch/riscv/Makefile')
| -rw-r--r-- | arch/riscv/Makefile | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile index 597b58b2d4c0..2372464ad27d 100644 --- a/arch/riscv/Makefile +++ b/arch/riscv/Makefile @@ -12,6 +12,8 @@ OBJCOPYFLAGS := -O binary LDFLAGS_vmlinux := ifeq ($(CONFIG_DYNAMIC_FTRACE),y) LDFLAGS_vmlinux := --no-relax + KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY + CC_FLAGS_FTRACE := -fpatchable-function-entry=8 endif ifeq ($(CONFIG_64BIT)$(CONFIG_CMODEL_MEDLOW),yy) |