================
@@ -613,32 +645,34 @@ void macho::foldIdenticalSections(bool onlyCfStrings) {
for (Defined *d : isec->symbols)
if (d->unwindEntry())
foldable.push_back(d->unwindEntry());
-
- // Some sections have embedded addends that foil ICF's hashing / equality
- // checks. (We can ignore embedded addends when doing ICF because the
same
- // information gets recorded in our Reloc structs.) We therefore create a
- // mutable copy of the section data and zero out the embedded addends
- // before performing any hashing / equality checks.
- if (isFoldableWithAddendsRemoved) {
- // We have to do this copying serially as the BumpPtrAllocator is not
- // thread-safe. FIXME: Make a thread-safe allocator.
- MutableArrayRef<uint8_t> copy = isec->data.copy(bAlloc());
- for (const Relocation &r : isec->relocs)
- target->relocateOne(copy.data() + r.offset, r, /*va=*/0,
- /*relocVA=*/0);
- isec->data = copy;
- }
- } else if (!isEhFrameSection(isec)) {
- // EH frames are gathered as foldables from unwindEntry above; give a
- // unique ID to everything else.
+ } else if (isEhFrameSection(isec)) {
+ // __eh_frame contains two types of records: FDEs and CIEs.
+ // Functions point to FDEs, which are already collected above via
+ // unwindEntry(). CIEs are shared headers and are not attached to
+ // individual functions. Collect only CIEs here so they can also be
hashed
+ // and deduplicated.
+ auto *obj = dyn_cast_or_null<ObjFile>(isec->getFile());
+ if (!onlyCfStrings && obj && !obj->fdes.contains(isec) &&
+ !isec->shouldOmitFromOutput())
+ foldable.push_back(isec);
+ } else {
+ // Give a unique ID to everything else.
isec->icfEqClass[0] = ++icfUniqueID;
}
}
----------------
ellishg wrote:
I added some logs here
```
for (auto *isec : foldable) {
for (auto &r : isec->relocs) {
errs() << isec << " " << isec->symbols[0]->getName() << " " << r.offset
<< "\n";
}
}
```
And got this output
```
0x281cf0 ltmp0 4
0x2821c0 EH_Frame 25
0x2821c0 EH_Frame 0
0x2821c0 EH_Frame 8
0x2821c0 EH_Frame 0
0x2821c0 EH_Frame 4
0x2821c0 EH_Frame 4
0x2825b0 _padB 4
0x2824d0 EH_Frame 25
0x2824d0 EH_Frame 0
0x2824d0 EH_Frame 8
0x2824d0 EH_Frame 0
0x2824d0 EH_Frame 4
0x2824d0 EH_Frame 4
0x282620 _foldA 4
0x282230 EH_Frame 25
0x282230 EH_Frame 0
0x282230 EH_Frame 8
0x282230 EH_Frame 0
0x282230 EH_Frame 4
0x282230 EH_Frame 4
...
```
We can see some relocations have an offset zero, which would cause
`getNormalizedData()` to zero out the first byte in the section. I think that
is the length byte and the size is already checked in `compareData()`, so it
might not cause incorrect folding in this case. But still this could lead to a
bug. This is the point I tried to make in
https://github.com/llvm/llvm-project/pull/213778#discussion_r3806288211.
https://github.com/llvm/llvm-project/pull/216895
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