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[llvm][ELF] Add ELF header/section header table size statistics #109345

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Merged
merged 2 commits into from
Sep 23, 2024
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[llvm][ELF] Add ELF header/section header table size statistics #109345

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[llvm][ELF] Add ELF header/section header table size statistics
aeubanks Sep 19, 2024
3e4fd31
add test
aeubanks Sep 20, 2024
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7 changes: 7 additions & 0 deletions llvm/lib/MC/ELFObjectWriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,8 @@ using namespace llvm;
namespace {
namespace stats {

STATISTIC(ELFHeaderBytes, "Total size of ELF headers");
STATISTIC(SectionHeaderBytes, "Total size of section headers table");
STATISTIC(AllocTextBytes, "Total size of SHF_ALLOC text sections");
STATISTIC(AllocROBytes, "Total size of SHF_ALLOC readonly sections");
STATISTIC(AllocRWBytes, "Total size of SHF_ALLOC read-write sections");
Expand Down Expand Up @@ -945,6 +947,7 @@ void ELFWriter::writeSectionHeader(uint32_t GroupSymbolIndex, uint64_t Offset,
}

void ELFWriter::writeSectionHeaders(const MCAssembler &Asm) {
uint64_t Start = W.OS.tell();
const unsigned NumSections = SectionTable.size();

// Null section first.
Expand Down Expand Up @@ -1008,6 +1011,8 @@ void ELFWriter::writeSectionHeaders(const MCAssembler &Asm) {

writeSectionHeader(GroupSymbolIndex, Offsets.first, Size, *Section);
}

stats::SectionHeaderBytes += W.OS.tell() - Start;
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Add a test?

If llvm-project ever gets https://maskray.me/blog/2024-03-31-a-compact-section-header-table-for-elf (impl:
https://github.com/MaskRay/llvm-project/tree/demo-cshdr ; which might need certain extent of agreement), this can be used to show the size difference due to -Wa,--cshdr :)

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I don't really want to hardcode the value of this stat in the test, and I'm not sure how else I'd test it?

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Encoding the value should be fine. It's very unlikely that the value will ever change.

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done

}

uint64_t ELFWriter::writeObject(MCAssembler &Asm) {
Expand All @@ -1023,6 +1028,8 @@ uint64_t ELFWriter::writeObject(MCAssembler &Asm) {
// Write out the ELF header ...
writeHeader(Asm);

stats::ELFHeaderBytes += W.OS.tell() - StartOffset;

// ... then the sections ...
SmallVector<std::pair<MCSectionELF *, SmallVector<unsigned>>, 0> Groups;
// Map from group section index to group
Expand Down
2 changes: 2 additions & 0 deletions llvm/test/CodeGen/X86/section-stats.ll
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Expand Up @@ -3,6 +3,8 @@

; CHECK-DAG: 1 elf-object-writer - Total size of SHF_ALLOC text sections
; CHECK-DAG: 1 elf-object-writer - Total size of SHF_ALLOC read-write sections
; CHECK-DAG: 512 elf-object-writer - Total size of section headers table
; CHECK-DAG: 64 elf-object-writer - Total size of ELF headers

target triple = "x86_64-unknown-linux-gnu"

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