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[BOLT] Refactor NewTextSegmentAddress handling #145950

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merged 1 commit into from
Jun 26, 2025
Merged

[BOLT] Refactor NewTextSegmentAddress handling #145950

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40 changes: 15 additions & 25 deletions bolt/lib/Rewrite/RewriteInstance.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -626,6 +626,9 @@ Error RewriteInstance::discoverStorage() {
NextAvailableAddress += BC->PageAlign;
}

NewTextSegmentAddress = NextAvailableAddress;
NewTextSegmentOffset = NextAvailableOffset;

if (!opts::UseGnuStack && !BC->IsLinuxKernel) {
// This is where the black magic happens. Creating PHDR table in a segment
// other than that containing ELF header is tricky. Some loaders and/or
Expand All @@ -652,6 +655,8 @@ Error RewriteInstance::discoverStorage() {

PHDRTableAddress = NextAvailableAddress;
PHDRTableOffset = NextAvailableOffset;
NewTextSegmentAddress = NextAvailableAddress;
NewTextSegmentOffset = NextAvailableOffset;

// Reserve space for 3 extra pheaders.
unsigned Phnum = Obj.getHeader().e_phnum;
Expand All @@ -664,14 +669,12 @@ Error RewriteInstance::discoverStorage() {

NextAvailableAddress += Phnum * sizeof(ELF64LEPhdrTy);
NextAvailableOffset += Phnum * sizeof(ELF64LEPhdrTy);
}

// Align at cache line.
NextAvailableAddress = alignTo(NextAvailableAddress, 64);
NextAvailableOffset = alignTo(NextAvailableOffset, 64);
// Align at cache line.
NextAvailableAddress = alignTo(NextAvailableAddress, 64);
NextAvailableOffset = alignTo(NextAvailableOffset, 64);
}

NewTextSegmentAddress = NextAvailableAddress;
NewTextSegmentOffset = NextAvailableOffset;
BC->LayoutStartAddress = NextAvailableAddress;

// Tools such as objcopy can strip section contents but leave header
Expand Down Expand Up @@ -4133,13 +4136,8 @@ void RewriteInstance::mapAllocatableSections(
}

if (SType == ST_READONLY) {
if (PHDRTableAddress) {
// Segment size includes the size of the PHDR area.
NewTextSegmentSize = NextAvailableAddress - PHDRTableAddress;
} else if (NewTextSegmentAddress) {
// Existing PHDR table would be updated.
if (NewTextSegmentAddress)
NewTextSegmentSize = NextAvailableAddress - NewTextSegmentAddress;
}
} else if (SType == ST_READWRITE) {
NewWritableSegmentSize = NextAvailableAddress - NewWritableSegmentAddress;
// Restore NextAvailableAddress if no new writable sections
Expand Down Expand Up @@ -4186,9 +4184,7 @@ void RewriteInstance::patchELFPHDRTable() {
// NOTE Currently .eh_frame_hdr appends to the last segment, recalculate
// last segments size based on the NextAvailableAddress variable.
if (!NewWritableSegmentSize) {
if (PHDRTableAddress)
NewTextSegmentSize = NextAvailableAddress - PHDRTableAddress;
else if (NewTextSegmentAddress)
if (NewTextSegmentAddress)
NewTextSegmentSize = NextAvailableAddress - NewTextSegmentAddress;
} else {
NewWritableSegmentSize = NextAvailableAddress - NewWritableSegmentAddress;
Expand All @@ -4201,15 +4197,9 @@ void RewriteInstance::patchELFPHDRTable() {
SmallVector<ELF64LEPhdrTy, 3> NewPhdrs;
ELF64LEPhdrTy NewPhdr;
NewPhdr.p_type = ELF::PT_LOAD;
if (PHDRTableAddress) {
NewPhdr.p_offset = PHDRTableOffset;
NewPhdr.p_vaddr = PHDRTableAddress;
NewPhdr.p_paddr = PHDRTableAddress;
} else {
NewPhdr.p_offset = NewTextSegmentOffset;
NewPhdr.p_vaddr = NewTextSegmentAddress;
NewPhdr.p_paddr = NewTextSegmentAddress;
}
NewPhdr.p_offset = NewTextSegmentOffset;
NewPhdr.p_vaddr = NewTextSegmentAddress;
NewPhdr.p_paddr = NewTextSegmentAddress;
NewPhdr.p_filesz = NewTextSegmentSize;
NewPhdr.p_memsz = NewTextSegmentSize;
NewPhdr.p_flags = ELF::PF_X | ELF::PF_R;
Expand Down Expand Up @@ -4270,7 +4260,7 @@ void RewriteInstance::patchELFPHDRTable() {
};

auto writeNewSegmentPhdrs = [&]() {
if (PHDRTableAddress || NewTextSegmentSize) {
if (NewTextSegmentSize) {
SmallVector<ELF64LE::Phdr, 3> NewPhdrs = createNewPhdrs();
OS.write(reinterpret_cast<const char *>(NewPhdrs.data()),
sizeof(ELF64LE::Phdr) * NewPhdrs.size());
Expand Down
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