Re: [PATCH v1 10/14] DCE/DSE: riscv: make every ex_table's name unique

[Fangrui Song]

On Fri, Nov 3, 2023 at 9:02 AM Yuan Tan <tanyuan@xxxxxxxxxxx> wrote:
>
> gc-sections require section names to be unique.

This is not precise, since a monolithic section can be garbage
collected as well.

https://maskray.me/blog/2021-02-28-linker-garbage-collection

"Without the options, the compiler tends to produce monolithic text
and data sections. The large sections make the GC coarse-grained and
they will likely be retained as a whole. ld --gc-sections can still
discard some sections, but the effect is likely very poor."


> Signed-off-by: Yuan Tan <tanyuan@xxxxxxxxxxx>
> Signed-off-by: Zhangjin Wu <falcon@xxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/asm-extable.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/asm-extable.h b/arch/riscv/include/asm/asm-extable.h
> index 00a96e7a9664..d0be5a838242 100644
> --- a/arch/riscv/include/asm/asm-extable.h
> +++ b/arch/riscv/include/asm/asm-extable.h
> @@ -9,10 +9,12 @@
>
>  #ifdef CONFIG_MMU
>
> +#include <linux/compiler.h>
> +
>  #ifdef __ASSEMBLY__
>
>  #define __ASM_EXTABLE_RAW(insn, fixup, type, data)     \
> -       .pushsection    __ex_table, "a";                \
> +       .pushsection    __SECTION_NAME(__ex_table), "a";                \
>         .balign         4;                              \
>         .long           ((insn) - .);                   \
>         .long           ((fixup) - .);                  \
> @@ -31,7 +33,7 @@
>  #include <asm/gpr-num.h>

__SECTION_NAME is probably added by a previous patch.
An alternative is to use the .section directive's `unique` feature
(binutils>=2.35).

>  #define __ASM_EXTABLE_RAW(insn, fixup, type, data)     \
> -       ".pushsection   __ex_table, \"a\"\n"            \
> +       ".pushsection " __SECTION_NAME(__ex_table) ", \"a\"\n"          \
>         ".balign        4\n"                            \
>         ".long          ((" insn ") - .)\n"             \
>         ".long          ((" fixup ") - .)\n"            \
> --
> 2.34.1
>