[PATCH 16/17] efi_loader: Move .dynamic out of .text in EFI

[Sam Edwards]

On Sun, Feb 23, 2025 at 11:34 PM Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
>
>
> Sam Edwards <cfsworks at gmail.com> schrieb am Mo., 24. Feb. 2025, 06:56:
>>
>> This was not proper: A .text section is SHT_PROGBITS, while the .dynamic
>> section is SHT_DYNAMIC. Attempting to combine them like this creates a
>> section type mismatch.
>>
>> It seems that while GNU ld does not complain, LLVM's lld considers this
>> an error.
>>
>> Signed-off-by: Sam Edwards <CFSworks at gmail.com>
>> Cc: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>> ---
>>  lib/efi_loader/elf_efi.ldsi | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/efi_loader/elf_efi.ldsi b/lib/efi_loader/elf_efi.ldsi
>> index dc4d1a3660e..acf02eba4d6 100644
>> --- a/lib/efi_loader/elf_efi.ldsi
>> +++ b/lib/efi_loader/elf_efi.ldsi
>> @@ -20,10 +20,10 @@ SECTIONS
>>                 *(.gnu.linkonce.t.*)
>>                 *(.srodata)
>>                 *(.rodata*)
>> -               . = ALIGN(16);
>> -               *(.dynamic);
>> -               . = ALIGN(512);
>>         }
>> +       . = ALIGN(16);
>> +       .dynamic : { *(.dynamic) }
>
>
> .dynamic is related to dynamic linking of libraries.
>
> Under which circumstances would we have content in .dynamic? Why would it be needed for executing an EFI application?

Hey Heinrich,

Apologies for the late response; I didn't have sufficient time/tuits
to get to this until now.

While EFI applications are indeed statically linked, they need to be
relocatable. The .dynamic section contains the ELF dynamic table
(exposed via the _DYNAMIC symbol), which is passed to _relocate by the
crt0_[arch]_efi.S stubs. _relocate finds the relocations table by
querying the DT_RELA/_RELASZ/_RELAENT entries in the dynamic table.
Normally, the PE loader handles relocation of EFI applications before
transferring control by applying the PE relocations in .reloc, but
generating PE-format relocations would require some toolchain
trickery. Hence the ELF dynamic information (and relocations) in a PE
file. :)

Happy Monday,
Sam

>
> Best regards
>
> Heinrich
>
>
>> +       . = ALIGN(512);
>>         .rela.dyn : { *(.rela.dyn) }
>>         .rela.plt : { *(.rela.plt) }
>>         .rela.got : { *(.rela.got) }
>> --
>> 2.45.2
>>