Re: [PATCH] MIPS: VDSO: Avoid including .got in dynamic segment

[Nick Desaulniers <ndesaulniers@google.com>]

On Tue, Jun 09, 2026 at 06:31:21PM -0700, Nathan Chancellor wrote:
> After commit 2db1ec80dfd5 ("MIPS: VDSO: Fold MIPS_DISABLE_VDSO into
> MIPS_GENERIC_GETTIMEOFDAY"), building ARCH=mips allnoconfig with LLVM=1
> shows some warnings from llvm-readelf while checking the VDSO for
> dynamic relocations:
> 
>   llvm-readelf: warning: 'arch/mips/vdso/vdso.so.dbg.raw': invalid PT_DYNAMIC size (0xa4)
>   llvm-readelf: warning: 'arch/mips/vdso/vdso.so.dbg.raw': PT_DYNAMIC dynamic table is invalid: SHT_DYNAMIC will be used
> 
> The blamed commit alters the link order of objects into vdso.so.raw,
> placing vgettimeofday.o after sigreturn.o. This ultimately results in
> the .text section shrinking slightly in size, which in turn changes the
> offset of the .dynamic section.
> 
>   -  [ 9] .text             PROGBITS        000002f0 0002f0 000930 00  AX  0   0 16
>   -  [10] .dynamic          DYNAMIC         00000c20 000c20 000090 08   A  5   0  4
>   +  [ 9] .text             PROGBITS        000002f0 0002f0 000924 00  AX  0   0 16
>   +  [10] .dynamic          DYNAMIC         00000c14 000c14 000090 08   A  5   0  4
> 
> Changing the offset of the .dynamic section causes the dynamic segment
> size to grow by the same amount, which triggers a warning in
> llvm-readelf because PT_DYNAMIC's p_filesz (0xa4) is no longer a
> multiple of its sh_entsize (8):
> 
>   -  DYNAMIC        0x000c20 0x00000c20 0x00000c20 0x00098 0x00098 R   0x10
>   +  DYNAMIC        0x000c14 0x00000c14 0x00000c14 0x000a4 0x000a4 R   0x10
> 
> The size of the dynamic segment was already incorrect before the blamed
> comment, as it should be 0x90 like the .dynamic section above (18
> entries at 8 bytes per entry); it just so happens that 0x98 % 8 is 0,
> whereas 0xa4 % 8 is 4, so there was no warning.
> 
> Looking at the section to segment mapping of the dynamic segment reveals
> that it includes the .got section, as it is implicitly placed after
> .dynamic by ld.lld's orphan section heuristics and inherits its segments
> from the linker script.
> 
>   [ 9] .text             PROGBITS        000002f0 0002f0 000924 00  AX  0   0 16
>   [10] .dynamic          DYNAMIC         00000c14 000c14 000090 08   A  5   0  4
>   [11] .got              PROGBITS        00000cb0 000cb0 000008 00 WAp  0   0 16
> 
>   Section to Segment mapping:
>    Segment Sections...
>     00     .mips_abiflags
>     01     .reginfo
>     02     .mips_abiflags .reginfo .hash .dynsym .dynstr .gnu.version .gnu.version_d .note .text .dynamic .got
>     03     .dynamic .got
>     04     .note
> 
> Explicitly describe the .got section in the MIPS VDSO linker script
> after .rodata, which switches back to the default text segment,
> resulting in a dynamic segment that is the exact size of the .dynamic
> section as expected with no other layout changes.
> 
>   -  DYNAMIC        0x000c14 0x00000c14 0x00000c14 0x000a4 0x000a4 R   0x10
>   +  DYNAMIC        0x000c14 0x00000c14 0x00000c14 0x00090 0x00090 R   0x4
> 
>   -   03     .dynamic .got
>   +   03     .dynamic
> 
> Closes: https://github.com/ClangBuiltLinux/linux/issues/2166
> Fixes: 2db1ec80dfd5 ("MIPS: VDSO: Fold MIPS_DISABLE_VDSO into MIPS_GENERIC_GETTIMEOFDAY")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the patch!
Acked-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> The fixes tag feels a little strong since it seems like it has just been
> luck up until this point that there has been no warning but I decided to
> be conservative and include it regardless. Feel free to remove it if you
> see fit.
> 
> I think this should go via timers/vdso with the blamed commit. I plan to
> send a follow up series for 7.3 to add '--orphan-handling' to the MIPS
> VDSO to avoid issues like this in the future but that can go via the
> MIPS tree, as it is not really a fix and I will need to properly test
> it.
> ---
>  arch/mips/vdso/vdso.lds.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/mips/vdso/vdso.lds.S b/arch/mips/vdso/vdso.lds.S
> index 05badf3ae0ff..278ab6444e98 100644
> --- a/arch/mips/vdso/vdso.lds.S
> +++ b/arch/mips/vdso/vdso.lds.S
> @@ -56,6 +56,7 @@ SECTIONS
>  	.dynamic	: { *(.dynamic) }		:text :dynamic
>  
>  	.rodata		: { *(.rodata*) }		:text
> +	.got		: { *(.got) }
>  
>  	_end = .;
>  	PROVIDE(end = .);
> 
> ---
> base-commit: 13f6218e6fe79dc64aed76d738b765b45f62492b
> change-id: 20260608-mips-vdso-fix-section-layout-262bc18d0c29
> 
> Best regards,
> --  
> Cheers,
> Nathan
>