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(-) 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 _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
