[llvm] [llvm-ar][Object] Use K_GNU instead of K_COFF for archives with no symtab. (PR #82898)

[Jacek Caban via llvm-commits]

https://github.com/cjacek created https://github.com/llvm/llvm-project/pull/82898

I noticed it due to a test failure in #82642 in a test that creates an archive with 'S' (no symbol table) option. Reader recognizes coff format from gnu format from presence of the extra symbol map member, so this can't work for archives with no symbol table. Just use gnu format in archive writer in such case.

>From 01b7c455f9fb57c3b22deddea3368d948a267316 Mon Sep 17 00:00:00 2001
From: Jacek Caban <jacek at codeweavers.com>
Date: Sat, 24 Feb 2024 23:34:31 +0100
Subject: [PATCH] [llvm-ar][Object] Use K_GNU instead of K_COFF for archives
 with no symtab.

---
 llvm/lib/Object/ArchiveWriter.cpp      |  7 +++---
 llvm/test/tools/llvm-ar/no-symtab.yaml | 32 ++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/tools/llvm-ar/no-symtab.yaml

diff --git a/llvm/lib/Object/ArchiveWriter.cpp b/llvm/lib/Object/ArchiveWriter.cpp
index 02f72521c8b544..9af2b6e94a270a 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -966,10 +966,12 @@ static Error writeArchiveToStream(raw_ostream &Out,
   SmallString<0> StringTableBuf;
   raw_svector_ostream StringTable(StringTableBuf);
   SymMap SymMap;
+  bool ShouldWriteSymtab = WriteSymtab != SymtabWritingMode::NoSymtab;
 
   // COFF symbol map uses 16-bit indexes, so we can't use it if there are too
-  // many members.
-  if (isCOFFArchive(Kind) && NewMembers.size() > 0xfffe)
+  // many members. COFF format also requires symbol table presence, so use
+  // GNU format when NoSymtab is requested.
+  if (isCOFFArchive(Kind) && (NewMembers.size() > 0xfffe || !ShouldWriteSymtab))
     Kind = object::Archive::K_GNU;
 
   // In the scenario when LLVMContext is populated SymbolicFile will contain a
@@ -998,7 +1000,6 @@ static Error writeArchiveToStream(raw_ostream &Out,
   uint64_t LastMemberHeaderOffset = 0;
   uint64_t NumSyms = 0;
   uint64_t NumSyms32 = 0; // Store symbol number of 32-bit member files.
-  bool ShouldWriteSymtab = WriteSymtab != SymtabWritingMode::NoSymtab;
 
   for (const auto &M : Data) {
     // Record the start of the member's offset
diff --git a/llvm/test/tools/llvm-ar/no-symtab.yaml b/llvm/test/tools/llvm-ar/no-symtab.yaml
new file mode 100644
index 00000000000000..7370c9b3235522
--- /dev/null
+++ b/llvm/test/tools/llvm-ar/no-symtab.yaml
@@ -0,0 +1,32 @@
+## Create archives with no symtab in various formats and check that we can read them.
+
+# RUN: yaml2obj %s -o %t.o
+# RUN: rm -f %t.*.a
+
+# RUN: llvm-ar --format=gnu rcS %t.gnu.a %t.o
+# RUN: llvm-ar --format=coff rcS %t.coff.a %t.o
+# RUN: llvm-ar --format=darwin rcS %t.darwin.a %t.o
+# RUN: llvm-ar --format=bsd rcS %t.bsd.a %t.o
+# RUN: llvm-ar --format=bigarchive rcS %t.bigarchive.a %t.o
+
+# RUN: llvm-nm --print-armap %t.gnu.a | FileCheck %s
+# RUN: llvm-nm --print-armap %t.coff.a | FileCheck %s
+# RUN: llvm-nm --print-armap %t.darwin.a | FileCheck %s
+# RUN: llvm-nm --print-armap %t.bsd.a | FileCheck %s
+# RUN: llvm-nm --print-armap %t.bigarchive.a | FileCheck %s
+
+# CHECK-NOT: Archive map
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name: .text
+    Type: SHT_PROGBITS
+Symbols:
+  - Name:    symbol
+    Binding: STB_GLOBAL
+    Section: .text