[BOLT] Refactor NewTextSegmentAddress handling (#145950)
Refactor the code for NewTextSegmentAddress to correctly point at the
true start of the segment when PHDR table is placed at the beginning. We
used to offset NewTextSegmentAddress by PHDR table plus cache line
alignment.
NFC for proper binaries. Some YAML binaries from our tests will diverge
due to bad segment address/offset alignment.
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 93bd93b..dc7591a 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -626,6 +626,9 @@
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
@@ -652,6 +655,8 @@
PHDRTableAddress = NextAvailableAddress;
PHDRTableOffset = NextAvailableOffset;
+ NewTextSegmentAddress = NextAvailableAddress;
+ NewTextSegmentOffset = NextAvailableOffset;
// Reserve space for 3 extra pheaders.
unsigned Phnum = Obj.getHeader().e_phnum;
@@ -664,14 +669,12 @@
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
@@ -4133,13 +4136,8 @@
}
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
@@ -4186,9 +4184,7 @@
// 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;
@@ -4201,15 +4197,9 @@
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;
@@ -4270,7 +4260,7 @@
};
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());
