[PATCH] D42659: [COFF] Clarify comment. NFC

[Shoaib Meenai via Phabricator via llvm-commits]

smeenai created this revision.
smeenai added reviewers: mstorsjo, rnk, ruiu.

Reid pointed out the string table for supporting long section names is a
BFD extension and the comments should reflect that. Explicitly spell out
link.exe's and binutil's behavior around section names and the rationale
for LLD's behavior.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D42659

Files:
  COFF/Writer.cpp


Index: COFF/Writer.cpp
===================================================================
--- COFF/Writer.cpp
+++ COFF/Writer.cpp
@@ -573,16 +573,18 @@
 }
 
 void Writer::createSymbolAndStringTable() {
-  // Name field in the section table is 8 byte long. Longer names need
-  // to be written to the string table. First, construct string table.
+  // PE/COFF images are limited to 8 byte section names. Longer names can be
+  // supported by writing a non-standard string table, but this string table is
+  // not mapped at runtime and the long names will therefore be inaccessible.
+  // link.exe always truncates section names to 8 bytes, whereas binutils always
+  // preserves long section names via the string table. LLD adopts a hybrid
+  // solution where discardable sections have long names preserved and
+  // non-discardable sections have their names truncated, to ensure that any
+  // section which is mapped at runtime also has its name mapped at runtime.
   for (OutputSection *Sec : OutputSections) {
     StringRef Name = Sec->getName();
     if (Name.size() <= COFF::NameSize)
       continue;
-    // If a section isn't discardable (i.e. will be mapped at runtime),
-    // prefer a truncated section name over a long section name in
-    // the string table that is unavailable at runtime. Note that link.exe
-    // always truncates, even for discardable sections.
     if ((Sec->getPermissions() & IMAGE_SCN_MEM_DISCARDABLE) == 0)
       continue;
     Sec->setStringTableOff(addEntryToStringTable(Name));


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