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[llvm][yaml2obj] Modify section header overriding timing #130942

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Merged
merged 8 commits into from
Sep 18, 2025
Merged

[llvm][yaml2obj] Modify section header overriding timing #130942

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701efbe
[llvm][yaml2obj] Modify section header overriding timing
cabbaken Mar 12, 2025
f079240
Distinguish ShOffset and Offset in program-header-size-offset.yaml, r…
cabbaken Mar 17, 2025
9260c30
Modify malformed-pt-dynamic.test to fix program header offset
cabbaken Mar 17, 2025
db32881
Optimize code style
cabbaken Mar 17, 2025
2b7f229
Add the check for the order of Offset and ShOffset
Jul 1, 2025
f943ab1
Fix tests about the change of `ShOffset` overriding timing
Jul 3, 2025
7908868
Fix comment format of program-header.yaml
Jul 11, 2025
4d88fa5
Remove unrelated comment
cabbaken Sep 9, 2025
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20 changes: 16 additions & 4 deletions llvm/lib/ObjectYAML/ELFEmitter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -206,6 +206,9 @@ template <class ELFT> class ELFState {
NameToIdxMap DynSymN2I;
ELFYAML::Object &Doc;

std::vector<std::pair<unsigned, ELFYAML::Section>>
SectionHeadersOverrideHelper;

StringSet<> ExcludedSectionHeaders;

uint64_t LocationCounter = 0;
Expand All @@ -226,6 +229,7 @@ template <class ELFT> class ELFState {
StringRef SecName, ELFYAML::Section *YAMLSec);
void initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
ContiguousBlobAccumulator &CBA);
void overrideSectionHeaders(std::vector<Elf_Shdr> &SHeaders);
void initSymtabSectionHeader(Elf_Shdr &SHeader, SymtabType STType,
ContiguousBlobAccumulator &CBA,
ELFYAML::Section *YAMLSec);
Expand Down Expand Up @@ -845,7 +849,7 @@ void ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
}

LocationCounter += SHeader.sh_size;
overrideFields<ELFT>(Sec, SHeader);
SectionHeadersOverrideHelper.push_back({SN2I.get(Sec->Name), *Sec});
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I'm struggling to follow why you can't just store Sec and SHeader in the vector (SHeader as a pointer, obviously)?

continue;
}

Expand Down Expand Up @@ -899,12 +903,17 @@ void ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
}

LocationCounter += SHeader.sh_size;

// Override section fields if requested.
overrideFields<ELFT>(Sec, SHeader);
SectionHeadersOverrideHelper.push_back({SN2I.get(Sec->Name), *Sec});
}
}

template <class ELFT>
void ELFState<ELFT>::overrideSectionHeaders(std::vector<Elf_Shdr> &SHeaders) {
for (std::pair<unsigned, ELFYAML::Section> &IndexAndSec :
SectionHeadersOverrideHelper)
overrideFields<ELFT>(&IndexAndSec.second, SHeaders[IndexAndSec.first]);
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I think it would just be simpler to update the overrideFields function to take the vector of pairs and iterate it over it inside the function, rather than have this additional function. If you want to rename it to overrideSectionHeaders for additional clarity, I'm not opposed to that.

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initImplicitHeader() will also use overrideFields(), so I defined a new function to call overrideFields().

}

template <class ELFT>
void ELFState<ELFT>::assignSectionAddress(Elf_Shdr &SHeader,
ELFYAML::Section *YAMLSec) {
Expand Down Expand Up @@ -2090,6 +2099,9 @@ bool ELFState<ELFT>::writeELF(raw_ostream &OS, ELFYAML::Object &Doc,
// Now we can decide segment offsets.
State.setProgramHeaderLayout(PHeaders, SHeaders);

// Override section fields if requested.
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Suggested change
// Override section fields if requested.
// Override section fields, if requested. This needs to happen after program header layout happens, because otherwise the layout will use the new values.

(and reflow to column width rules of course)

State.overrideSectionHeaders(SHeaders);

bool ReachedLimit = CBA.getOffset() > MaxSize;
if (Error E = CBA.takeLimitError()) {
// We report a custom error message instead below.
Expand Down
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