[llvm-nm] Print 'I' for import table data in COFF

[mstorsjo]

Summary

The character gets uppercased into 'I' when it's a global symbol.

In GNU binutils, nm prints 'I' for symbols classified by bfd_is_ind_section - which probably isn't exactly/only import tables.

When building for win32, (some incarnations of?) libtool has got rules that try to inspect linked libraries, and in order to be sure that it is linking to a DLL import library as opposed to a static library, it expects to find the string " I " in the output of $NM when run on such an import library.

GNU binutils nm also flags all of the .idata$X chunks as 'i' (while this patch only makes it set on .idata$2 and .idata$6) and also flags impfunction as 'I'.

[rnk]

lgtm

[smeenai]

GNU binutils nm also flags all of the .idata$X chunks as 'i' (while this patch only makes it set on .idata$2 and .idata$6) and also flags impfunction as 'I'.

This is just a consequence of how LLVM treats short import libraries, right? Considering that your patch returns 'i' for any .idata section, but short import libraries contain the ILT (.idata$4) and IAT (.idata$5) sections as COFFImportFile rather than COFFObjectFile.

[mstorsjo]

In D39540#914142, @smeenai wrote:

GNU binutils nm also flags all of the .idata$X chunks as 'i' (while this patch only makes it set on .idata$2 and .idata$6) and also flags impfunction as 'I'.

This is just a consequence of how LLVM treats short import libraries, right? Considering that your patch returns 'i' for any .idata section, but short import libraries contain the ILT (.idata$4) and IAT (.idata$5) sections as COFFImportFile rather than COFFObjectFile.

There's a few such cases as well, but the ones I meant get a '?' instead because (I think) they trigger this case:

Expected<section_iterator> SecIOrErr = SymI->getSection();
if (!SecIOrErr) {
  consumeError(SecIOrErr.takeError());
  return '?';
}

(These are symbols pointing to zero byte sections.)

llvm/trunk/test/tools/llvm-nm/X86/importlibrary.test

 # RUN: llvm-nm -B %S/Inputs/example.lib | FileCheck --match-full-lines %s
 
+CHECK: 00000000 I __IMPORT_DESCRIPTOR_example
+CHECK: 00000000 I __NULL_IMPORT_DESCRIPTOR
 CHECK: 00000000 R __imp__constant
 CHECK: 00000000 R _constant
 CHECK: 00000000 D __imp__data
 CHECK: 00000000 T __imp__function
 CHECK: 00000000 T _function

llvm/trunk/tools/llvm-nm/llvm-nm.cpp

if (!COFF::isReservedSectionNumber(Symb.getSectionNumber())) {
     Expected<section_iterator> SecIOrErr = SymI->getSection();
     if (!SecIOrErr) {
       consumeError(SecIOrErr.takeError());
       return '?';
     }
     section_iterator SecI = *SecIOrErr;
     const coff_section *Section = Obj.getCOFFSection(*SecI);
     Characteristics = Section->Characteristics;
+    StringRef SectionName;
+    Obj.getSectionName(Section, SectionName);
+    if (SectionName.startswith(".idata"))
+      return 'i';
   }
 
   switch (Symb.getSectionNumber()) {
   case COFF::IMAGE_SYM_DEBUG:
     return 'n';
   default:
     // Check section type.
     if (Characteristics & COFF::IMAGE_SCN_CNT_CODE)