GCC somehow manages to place some of the symbols from main.c into .rel.dyn section:

mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn' from `init/main.o' being placed in section `.rel.dyn'

I couldn't catch up the exact symbol, but seems like it's harmless to discard it from the final vmlinux as kernel doesn't use or support dynamic relocations.

Misc: sort DISCARDS section entries alphabetically.

Signed-off-by: Alexander Lobakin alobakin@pm.me --- arch/mips/kernel/vmlinux.lds.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 83e27a181206..1c3c2e903062 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -221,9 +221,10 @@ SECTIONS /* ABI crap starts here */ *(.MIPS.abiflags) *(.MIPS.options) + *(.eh_frame) *(.options) *(.pdr) *(.reginfo) - *(.eh_frame) + *(.rel.dyn) } }

在 2021/1/5 下午3:39, Fāng-ruì Sòng 写道:

On Mon, Jan 4, 2021 at 4:21 AM Alexander Lobakin alobakin@pm.me wrote:

...

GCC somehow manages to place some of the symbols from main.c into .rel.dyn section:

mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn' from `init/main.o' being placed in section `.rel.dyn'

I couldn't catch up the exact symbol, but seems like it's harmless to discard it from the final vmlinux as kernel doesn't use or support dynamic relocations.

Misc: sort DISCARDS section entries alphabetically.

Signed-off-by: Alexander Lobakin alobakin@pm.me

arch/mips/kernel/vmlinux.lds.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S index 83e27a181206..1c3c2e903062 100644 --- a/arch/mips/kernel/vmlinux.lds.S +++ b/arch/mips/kernel/vmlinux.lds.S @@ -221,9 +221,10 @@ SECTIONS /* ABI crap starts here */ *(.MIPS.abiflags) *(.MIPS.options)

•           *(.eh_frame)
             *(.options)
             *(.pdr)
             *(.reginfo)
  

•           *(.eh_frame)
  

•           *(.rel.dyn)
     }
  

  }

-- 2.30.0

(I don't know why I am on the CC list since I know little about mips... Anyway, I know the LLD linker's behavior in case that was the intention... )

I think it'd be good to know the reason why these dynamic relocations are produced and fix the root cause.

arch/x86/kernel/vmlinux.lds.S asserts no dynamic relocation: ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")

Hi all,

Runtime .rela can't be avoided as MIPS kernel can't be built with fPIC. Our relocatable kernel uses another approach, fixup dynamic relocations at boot time.

abicalls simply gave us too much overhead on PIC code, which is unacceptable for kernel.

In my local tests, PIC kernel reduced unix bench results for around 30%.

For MIPS Release6 and afterwards, we may utilize new pcrel instructions to reduce overhead but for older ISA I don't have any idea.

Thanks.

- Jiaxun

Now, after that all the sections are explicitly described and declared in vmlinux.lds.S, we can enable ld orphan warnings to prevent from missing any new sections in future.

Signed-off-by: Alexander Lobakin alobakin@pm.me --- arch/mips/Kconfig | 1 + 1 file changed, 1 insertion(+)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index d68df1febd25..d3e64cc0932b 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -18,6 +18,7 @@ config MIPS select ARCH_USE_QUEUED_SPINLOCKS select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU select ARCH_WANT_IPC_PARSE_VERSION + select ARCH_WANT_LD_ORPHAN_WARN select BUILDTIME_TABLE_SORT select CLONE_BACKWARDS select CPU_NO_EFFICIENT_FFS if (TARGET_ISA_REV < 1)