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    Subject[PATCH -next V6 2/7] riscv: ftrace: Remove wasted nops for !RISCV_ISA_C
    Date
    From: Guo Ren <guoren@linux.alibaba.com>

    When CONFIG_RISCV_ISA_C=n, -fpatchable-function-entry=8 would generate
    more nops than we expect. Because it treat nop opcode as 0x00000013
    instead of 0x0001.

    Dump of assembler code for function dw_pcie_free_msi:
    0xffffffff806fce94 <+0>: sd ra,-8(sp)
    0xffffffff806fce98 <+4>: auipc ra,0xff90f
    0xffffffff806fce9c <+8>: jalr -684(ra) # 0xffffffff8000bbec
    <ftrace_caller>
    0xffffffff806fcea0 <+12>: ld ra,-8(sp)
    0xffffffff806fcea4 <+16>: nop /* wasted */
    0xffffffff806fcea8 <+20>: nop /* wasted */
    0xffffffff806fceac <+24>: nop /* wasted */
    0xffffffff806fceb0 <+28>: nop /* wasted */
    0xffffffff806fceb4 <+0>: addi sp,sp,-48
    0xffffffff806fceb8 <+4>: sd s0,32(sp)
    0xffffffff806fcebc <+8>: sd s1,24(sp)
    0xffffffff806fcec0 <+12>: sd s2,16(sp)
    0xffffffff806fcec4 <+16>: sd s3,8(sp)
    0xffffffff806fcec8 <+20>: sd ra,40(sp)
    0xffffffff806fcecc <+24>: addi s0,sp,48

    Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
    Signed-off-by: Guo Ren <guoren@kernel.org>
    ---
    arch/riscv/Makefile | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
    index 12d91b0a73d8..ea5a91da6897 100644
    --- a/arch/riscv/Makefile
    +++ b/arch/riscv/Makefile
    @@ -11,7 +11,11 @@ LDFLAGS_vmlinux :=
    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
    +endif
    endif

    ifeq ($(CONFIG_CMODEL_MEDLOW),y)
    --
    2.36.1
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