Re: [PATCH 1/2] powerpc/vdso: Remove unused ENTRY in linker scripts

[Nick Desaulniers <ndesaulniers@google.com>]

On Mon, May 9, 2022 at 1:46 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> When linking vdso{32,64}.so.dbg with ld.lld, there is a warning about
> not finding _start for the starting address:
>
>   ld.lld: warning: cannot find entry symbol _start; not setting start address
>   ld.lld: warning: cannot find entry symbol _start; not setting start address
>
> Looking at GCC + GNU ld, the entry point address is 0x0:
>
>   $ llvm-readelf -h vdso{32,64}.so.dbg &| rg "(File|Entry point address):"
>   File: vdso32.so.dbg
>     Entry point address:               0x0
>   File: vdso64.so.dbg
>     Entry point address:               0x0
>
> This matches what ld.lld emits:
>
>   $ powerpc64le-linux-gnu-readelf -p .comment vdso{32,64}.so.dbg
>
>   File: vdso32.so.dbg
>
>   String dump of section '.comment':
>     [     0]  Linker: LLD 14.0.0
>     [    14]  clang version 14.0.0 (Fedora 14.0.0-1.fc37)
>
>   File: vdso64.so.dbg
>
>   String dump of section '.comment':
>     [     0]  Linker: LLD 14.0.0
>     [    14]  clang version 14.0.0 (Fedora 14.0.0-1.fc37)
>
>   $ llvm-readelf -h vdso{32,64}.so.dbg &| rg "(File|Entry point address):"
>   File: vdso32.so.dbg
>     Entry point address:               0x0
>   File: vdso64.so.dbg
>     Entry point address:               0x0
>
> Remove ENTRY to remove the warning, as it is unnecessary for the vDSO to
> function correctly.

Right, the vdso is going to be injected into the process' mappings;
what would it even mean for a DSO to have an entry point?
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  arch/powerpc/kernel/vdso/vdso32.lds.S | 1 -
>  arch/powerpc/kernel/vdso/vdso64.lds.S | 1 -
>  2 files changed, 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/vdso/vdso32.lds.S b/arch/powerpc/kernel/vdso/vdso32.lds.S
> index 58e0099f70f4..e0d19d74455f 100644
> --- a/arch/powerpc/kernel/vdso/vdso32.lds.S
> +++ b/arch/powerpc/kernel/vdso/vdso32.lds.S
> @@ -13,7 +13,6 @@ OUTPUT_FORMAT("elf32-powerpcle", "elf32-powerpcle", "elf32-powerpcle")
>  OUTPUT_FORMAT("elf32-powerpc", "elf32-powerpc", "elf32-powerpc")
>  #endif
>  OUTPUT_ARCH(powerpc:common)
> -ENTRY(_start)
>
>  SECTIONS
>  {
> diff --git a/arch/powerpc/kernel/vdso/vdso64.lds.S b/arch/powerpc/kernel/vdso/vdso64.lds.S
> index 0288cad428b0..1a4a7bc4c815 100644
> --- a/arch/powerpc/kernel/vdso/vdso64.lds.S
> +++ b/arch/powerpc/kernel/vdso/vdso64.lds.S
> @@ -13,7 +13,6 @@ OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle")
>  OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc")
>  #endif
>  OUTPUT_ARCH(powerpc:common64)
> -ENTRY(_start)
>
>  SECTIONS
>  {
> --
> 2.36.1
>


-- 
Thanks,
~Nick Desaulniers