[LLD][ELF] Move fixSectionAlignments() before first call to assignAddresses()

[peter.smith]

Summary

The fixSectionAlignments() function may alter the alignment of some OutputSections, this is likely to alter the addresses calculated earlier in assignAddresses(). By moving the call to fixSectionAlignments() we make sure that assignAddresses() is consistent with the early calculation used for RangeThunks and the final call just before writing the image.

This difference in address between the first call the assignAddresses() and the second may, with some linker scripts, cause some range-thunk calculations to go wrong, however for the majority of links it won't affect the relative offsets between callers and callees.

It is more important for a fix for pr33463 https://bugs.llvm.org/show_bug.cgi?id=33463 as the sequence of instructions that trigger the cortex-a53 errata are sensitive to address modulo 0x1000.

[peter.smith]

General ping for the -fix-cortex-a53-843419 patch set. Collectively these fix pr33463 which would be necessary to fix to allow lld to be used to build Android on AArch64.

• D36739
• D36742
• D36745
• D36749

[peter.smith]

General ping for the -fix-cortex-a53-843419 patch set. Collectively these fix pr33463 which would be necessary to fix in order for lld to be used to build Android on AArch64.

• D36739
• D36742
• D36745
• D36749

[ruiu]

LGTM

lld/trunk/ELF/Writer.cpp

template <class ELFT> void Writer<ELFT>::run() {
   // Now that we have a complete set of output sections. This function
   // completes section contents. For example, we need to add strings
   // to the string table, and add entries to .got and .plt.
   // finalizeSections does that.
   finalizeSections();
   if (ErrorCount)
     return;
 
-  if (!Script->Opt.HasSections && !Config->Relocatable)
-    fixSectionAlignments();
-
   // If -compressed-debug-sections is specified, we need to compress
   // .debug_* sections. Do it right now because it changes the size of
   // output sections.
   parallelForEach(OutputSections,
                   [](OutputSection *Sec) { Sec->maybeCompress<ELFT>(); });
 
   // Generate assignments for predefined symbols (e.g. _end or _etext)
   // before assigning addresses. These symbols may be referred to from
applySynthetic({InX::DynSymTab,    InX::Bss,
                   InX::IgotPlt,      InX::GotPlt,
                   In<ELFT>::RelaDyn, In<ELFT>::RelaIplt,
                   In<ELFT>::RelaPlt, InX::Plt,
                   InX::Iplt,         In<ELFT>::EhFrameHdr,
                   In<ELFT>::VerSym,  In<ELFT>::VerNeed,
                   InX::Dynamic},
                  [](SyntheticSection *SS) { SS->finalizeContents(); });
 
+  if (!Script->Opt.HasSections && !Config->Relocatable)
+    fixSectionAlignments();
+
   // Some architectures use small displacements for jump instructions.
   // It is linker's responsibility to create thunks containing long
   // jump instructions if jump targets are too far. Create thunks.
   if (Target->NeedsThunks) {
     // FIXME: only ARM Interworking and Mips LA25 Thunks are implemented,
     // these
     // do not require address information. To support range extension Thunks
     // we need to assign addresses so that we can tell if jump instructions