[LinkerScript] Fix bug in Segment::assignVirtualAddress()

[rafaelauler]

Summary

When calculating the start address and size of a segment, lld mistakenly
attributes the start address of the last segment slice to the whole segment
when it should consider the start address of the first slice. In this case, in a
multi-slice segment, Segment::assignVirtualAddress() will return a wrong
segment start address to TargetLayout::assignVirtualAddress(). The effect of
this miscalculation is to allocate some program headers in unnecessarily far
away addresses.

This will be tested in my next patch.

[• rafael]

testcase?

[rafaelauler]

This is tested in D10952, which is a patch that takes advantage of segments with multiple slices and frequently triggers the bug handled here. Without this patch, D10952 will break an existing test.

[rafaelauler]

Ping

[• rafael]

LGTM

lld/trunk/lib/ReaderWriter/ELF/SegmentChunks.cpp

template <class ELFT> void Segment<ELFT>::assignVirtualAddress(uint64_t addr) {
   slice->setStart(startSection);
   slice->setVirtualAddr(curSliceAddress);
   slice->setMemSize(curSliceSize);
   slice->setSections(make_range(startSectionIter, _sections.end()));
   slice->setAlign(sliceAlign);
 
   // Set the segment memory size and the virtual address.
   this->setMemSize(curSliceAddress - startAddr + curSliceSize);
-  this->setVirtualAddr(curSliceAddress);
+  this->setVirtualAddr(startAddr);
   std::stable_sort(_segmentSlices.begin(), _segmentSlices.end(),
                    SegmentSlice<ELFT>::compare_slices);
 }
 
 // Write the Segment
 template <class ELFT>
 void Segment<ELFT>::write(ELFWriter *writer, TargetLayout<ELFT> &layout,
                           llvm::FileOutputBuffer &buffer) {