Warn when an output section name is longer than 8 characters

Recent versions of Microsoft's dumpbin tool cannot handle such PE files.
LLVM tools and GNU tools can, and use this to encode long section names
like ".debug_info", which is commonly used for DWARF. Don't do this in
mingw mode or when -debug:dwarf is passed, since the user probably wants
long section names for DWARF sections.

PR43754

Reviewers: ruiu, mstorsjo

Differential Revision: https://reviews.llvm.org/D69594

Author: rnk

lld/COFF/Config.h

@@ -218,6 +218,7 @@ struct Configuration {
   bool warnMissingOrderSymbol = true;
   bool warnLocallyDefinedImported = true;
   bool warnDebugInfoUnusable = true;
+  bool warnLongSectionNames = true;
   bool incremental = true;
   bool integrityCheck = false;
   bool killAt = false;

lld/COFF/Driver.cpp

@@ -1188,6 +1188,8 @@ void LinkerDriver::link(ArrayRef<const char *> argsArr) {
         config->warnDebugInfoUnusable = false;
       else if (s == "4217")
         config->warnLocallyDefinedImported = false;
+      else if (s == "longsections")
+        config->warnLongSectionNames = false;
       // Other warning numbers are ignored.
     }
   }
@@ -1527,6 +1529,11 @@ void LinkerDriver::link(ArrayRef<const char *> argsArr) {
   config->debugGHashes = debug == DebugKind::GHash;
   config->debugSymtab = debug == DebugKind::Symtab;
 
+  // Don't warn about long section names, such as .debug_info, for mingw or when
+  // -debug:dwarf is requested.
+  if (config->mingw || config->debugDwarf)
+    config->warnLongSectionNames = false;
+
   config->mapFile = getMapFile(args);
 
   if (config->incremental && args.hasArg(OPT_profile)) {

lld/COFF/Writer.cpp

@@ -1148,6 +1148,11 @@ void Writer::createSymbolAndStringTable() {
       continue;
     if ((sec->header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0)
       continue;
+    if (config->warnLongSectionNames) {
+      warn("section name " + sec->name +
+           " is longer than 8 characters and will use a non-standard string "
+           "table");
+    }
     sec->setStringTableOff(addEntryToStringTable(sec->name));
   }
 

lld/test/COFF/long-section-name.test

@@ -1,8 +1,18 @@
 # RUN: yaml2obj < %s > %t.obj
-# RUN: lld-link /out:%t.exe /entry:main %t.obj
+# RUN: lld-link /out:%t.exe /entry:main %t.obj 2>&1 | FileCheck %s --check-prefix=WARN
 # RUN: llvm-readobj --sections %t.exe | FileCheck %s
-# RUN: lld-link /debug /out:%t2.exe /entry:main %t.obj
+# RUN: lld-link /debug /out:%t2.exe /entry:main %t.obj 2>&1 | FileCheck %s --check-prefix=WARN
 # RUN: llvm-readobj --sections %t2.exe | FileCheck %s
+#
+# No warnings in mingw mode or with ignore flag.
+# RUN: lld-link /out:%t.exe /entry:main %t.obj /ignore:longsections 2>&1 | FileCheck %s --check-prefix=IGNORE --allow-empty
+# RUN: lld-link /out:%t.exe /entry:main %t.obj -lldmingw 2>&1 | FileCheck %s --check-prefix=IGNORE --allow-empty
+# RUN: lld-link /out:%t.exe /entry:main %t.obj -debug:dwarf 2>&1 | FileCheck %s --check-prefix=IGNORE --allow-empty
+
+# WARN: warning: section name .data_long_section_name is longer than 8 characters and will use a non-standard string table
+# WARN: warning: section name .text_long_section_name is longer than 8 characters and will use a non-standard string table
+
+# IGNORE-NOT: warning:
 
 # CHECK: Name: .eh_fram (
 # CHECK: Name: .data_long_section_name