On 2 December 2015 at 17:06, Ard Biesheuvel <[email protected]> wrote:
> Unlike GNU ld, which can be instructed to emit symbol based static
> relocations into fully linked binaries using the --emit-relocs command
> line switch, the RVCT armlink tool can only emit dynamic relocations
> into the PT_DYNAMIC segment.
>
> This has two consequences
> . we can only identify absolute relocations, so there is no way to fix
> up relative relocations between sections, or check their validity in
> the PE/COFF layout
> . the r_offset fields of the PT_DYNAMIC DT_REL entries are relative
> either to the base of the image or to any of its segments but *not* to
> the base of the input section that contains the location they refer
> to, and converting them to PE/COFF image offsets is non-trivial unless
> the sections are laid out in the same way in the ELF and PE/COFF
> versions of the binary.
>
> There is really only one way to deal with this, and that is to require
> that the ELF and PE/COFF versions of the binary are identical in memory.
> So enforce that in the code.
>
> Also, fix the utterly broken relocation fixup code that dereferences
> ELF32_R_SYM(r_info) both as a 1-based program header index and a 0-based
> section header index. If this code ever produced working binaries, it
> was purely by chance.
>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <[email protected]>
> ---
> BaseTools/Source/C/GenFw/Elf32Convert.c | 36 ++++++++++++++------
> 1 file changed, 26 insertions(+), 10 deletions(-)
>
@Liming, Yonghong
If there are no objections to this patch (if affects EM_ARM only), I
would like to proceed and apply it.
Thanks,
Ard.
> diff --git a/BaseTools/Source/C/GenFw/Elf32Convert.c
> b/BaseTools/Source/C/GenFw/Elf32Convert.c
> index 469394540e6a..eede64576940 100644
> --- a/BaseTools/Source/C/GenFw/Elf32Convert.c
> +++ b/BaseTools/Source/C/GenFw/Elf32Convert.c
> @@ -804,9 +804,7 @@ WriteRelocations32 (
> UINTN RelSize;
> UINTN RelOffset;
> UINTN K;
> - UINT8 *Targ;
> Elf32_Phdr *DynamicSegment;
> - Elf32_Phdr *TargetSegment;
>
> for (Index = 0, FoundRelocations = FALSE; Index < mEhdr->e_shnum; Index++)
> {
> Elf_Shdr *RelShdr = GetShdrByIndex(Index);
> @@ -957,6 +955,31 @@ WriteRelocations32 (
> Error (NULL, 0, 3000, "Invalid", "%s bad ARM dynamic
> relocations.", mInImageName);
> }
>
> + for (Index = 0; Index < mEhdr->e_shnum; Index++) {
> + Elf_Shdr *shdr = GetShdrByIndex(Index);
> +
> + //
> + // The PT_DYNAMIC section contains DT_REL relocations whose
> r_offset
> + // field is relative to the base of a segment (or the entire
> image),
> + // and not to the base of an ELF input section as is the case for
> + // SHT_REL sections. This means that we cannot fix up such
> relocations
> + // unless we cross-reference ELF sections and segments, considering
> + // that the output placement recorded in mCoffSectionsOffset[] is
> + // section based, not segment based.
> + //
> + // Fortunately, there is a simple way around this: we require that
> the
> + // in-memory layout of the ELF and PE/COFF versions of the binary
> is
> + // identical. That way, r_offset will retain its validity as a
> PE/COFF
> + // image offset, and we can record it in the COFF fixup table
> + // unmodified.
> + //
> + if (shdr->sh_addr != mCoffSectionsOffset[Index]) {
> + Error (NULL, 0, 3000,
> + "Invalid", "%s: PT_DYNAMIC relocations require identical ELF
> and PE/COFF section offsets.",
> + mInImageName);
> + }
> + }
> +
> for (K = 0; K < RelSize; K += RelElementSize) {
>
> if (DynamicSegment->p_paddr == 0) {
> @@ -973,14 +996,7 @@ WriteRelocations32 (
> break;
>
> case R_ARM_RABS32:
> - TargetSegment = GetPhdrByIndex (ELF32_R_SYM (Rel->r_info) - 1);
> -
> - // Note: r_offset in a memory address. Convert it to a pointer
> in the coff file.
> - Targ = mCoffFile + mCoffSectionsOffset[ ELF32_R_SYM( Rel->r_info
> ) ] + Rel->r_offset - TargetSegment->p_vaddr;
> -
> - *(UINT32 *)Targ = *(UINT32 *)Targ + mCoffSectionsOffset
> [ELF32_R_SYM( Rel->r_info )];
> -
> - CoffAddFixup (mCoffSectionsOffset[ELF32_R_SYM (Rel->r_info)] +
> (Rel->r_offset - TargetSegment->p_vaddr), EFI_IMAGE_REL_BASED_HIGHLOW);
> + CoffAddFixup (Rel->r_offset, EFI_IMAGE_REL_BASED_HIGHLOW);
> break;
>
> default:
> --
> 1.9.1
>
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