[llvm-objcopy] Simplify SHT_NOBITS -> SHT_PROGBITS promotion
GNU objcopy uses bfd_elf_get_default_section_type to decide the candidate section type,
which roughly translates to our [a] (I assume SEC_COMMON implies SHF_ALLOC):
(!(Sec.Flags & ELF::SHF_ALLOC) || Flags & (SectionFlag::SecContents | SectionFlag::SecLoad)))
Then, it updates the section type in bfd/elf.c:elf_fake_sections if:
if (this_hdr->sh_type == SHT_NULL)
this_hdr->sh_type = sh_type; // common case
else if (this_hdr->sh_type == SHT_NOBITS
&& sh_type == SHT_PROGBITS
&& (asect->flags & SEC_ALLOC) != 0) // uncommon case
...
this_hdr->sh_type = sh_type;
If the following condition is met the uncommon branch is executed:
if (elf_section_type (osec) == SHT_NULL
&& (osec->flags == isec->flags
|| (final_link
&& ((osec->flags ^ isec->flags)
& ~(SEC_LINK_ONCE | SEC_LINK_DUPLICATES | SEC_RELOC)) == 0)))
I suggest we just ignore this clause and follow the common case
behavior, which is done in this patch. Rationales to do so:
If --set-section-flags is a no-op (osec->flags == isec->flags)
(corresponds to the "readonly" test in set-section-flags.test), GNU
objcopy will require (Sec.Flags & ELF::SHF_ALLOC). [a] is essentially:
Flags & (SectionFlag::SecContents | SectionFlag::SecLoad)
This special case is not really useful. Non-SHF_ALLOC SHT_NOBITS
sections do not make much sense and it doesn't matter if they are
SHT_NOBITS or SHT_PROGBITS.
For all other RUN lines in set-section-flags.test, the new behavior
matches GNU objcopy, i.e. this patch improves compatibility.
Differential Revision: https://reviews.llvm.org/D60189
llvm-svn: 359639
diff --git a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
index 7e99116..9b21190 100644
--- a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
@@ -99,13 +99,12 @@
static void setSectionFlagsAndType(SectionBase &Sec, SectionFlag Flags) {
Sec.Flags = getSectionFlagsPreserveMask(Sec.Flags, getNewShfFlags(Flags));
- // Certain flags also promote SHT_NOBITS to SHT_PROGBITS. Don't change other
- // section types (RELA, SYMTAB, etc.).
- const SectionFlag NoBitsToProgBitsMask =
- SectionFlag::SecContents | SectionFlag::SecLoad | SectionFlag::SecNoload |
- SectionFlag::SecCode | SectionFlag::SecData | SectionFlag::SecRom |
- SectionFlag::SecDebug;
- if (Sec.Type == SHT_NOBITS && (Flags & NoBitsToProgBitsMask))
+ // In GNU objcopy, certain flags promote SHT_NOBITS to SHT_PROGBITS. This rule
+ // may promote more non-ALLOC sections than GNU objcopy, but it is fine as
+ // non-ALLOC SHT_NOBITS sections do not make much sense.
+ if (Sec.Type == SHT_NOBITS &&
+ (!(Sec.Flags & ELF::SHF_ALLOC) ||
+ Flags & (SectionFlag::SecContents | SectionFlag::SecLoad)))
Sec.Type = SHT_PROGBITS;
}