[PATCH] [ELF] Fix .init_array initialization

[zatrazz]

Summary

Some compilers may not add the section symbol in '.symtab' for the
.init_array and 'ldd' just ignore it. It results in global constructor
not being called in final executable.

This patch add both '.init_array' and '.fini_array' to be added in
Atom graph generation even when the section contains no symbol. An
already existing testcase is modified to check for such scenario.

The patch fixes the llvm test-suite regressions for both Single
and MultiSource files.

[ruiu]

LGTM

lib/ReaderWriter/ELF/ELFFile.h

if (!shdr || !sectionOccupiesMemorySpace(shdr))
       return ArrayRef<uint8_t>();
     return _objFile->getSectionContents(shdr);
   }
 
   /// Determines if the target wants to create an atom for a section that has no
   /// symbol references.
   bool handleSectionWithNoSymbols(const Elf_Shdr *shdr,
                                   std::vector<Elf_Sym_Iter> &syms) const {
-    return shdr && (shdr->sh_type == llvm::ELF::SHT_PROGBITS) && syms.empty();
+    return shdr &&
+           (shdr->sh_type == llvm::ELF::SHT_PROGBITS ||
+            shdr->sh_type == llvm::ELF::SHT_INIT_ARRAY ||
+            shdr->sh_type == llvm::ELF::SHT_FINI_ARRAY) &&
+           syms.empty();
   }
 
   /// Handle creation of atoms for .gnu.linkonce sections.
   std::error_code handleGnuLinkOnceSection(
       const Elf_Shdr *section,
       llvm::StringMap<std::vector<ELFDefinedAtom<ELFT> *>> &atomsForSection);
 
   // Handle COMDAT scetions.

test/elf/init_array.test

 # Test .init_array.
 # Generated from the following C code:
 #
 # static void
 # init () {}
 #
 # static void (*const init_array []) ()
 #  __attribute__ ((used, section (".init_array"), aligned (sizeof (void *))))
 #  = { init };
 #
 # int
 # main() { return (0); }
+#
+# Note: both STT_OBJECT and STT_SECTION for .init_array are commented in yaml
+# declaration to check if lld correct adds the object's .init_array when the
+# section has no symbol (some compilers may create object with this behavior,
+# specially for C++ global constructors).
 
 #RUN: yaml2obj -format=elf %s -o=%t.o
 #RUN: lld -flavor gnu -target x86_64 %t.o -o %t -e=main
 #RUN: llvm-objdump -t -section-headers %t | FileCheck %s
 
 #CHECK: .init_array {{[0-9]+}} [[ADDR:[0-9]+]]
 #CHECK: [[ADDR]] l *ABS* {{[0-9]+}} .hidden __init_array_start
 
Relocations:
         Addend:          32
 Symbols:
   Local:
     - Name:            init
       Type:            STT_FUNC
       Section:         .text
       Value:           0x0000000000000020
       Size:            0x0000000000000006
-    - Name:            init_array
-      Type:            STT_OBJECT
-      Section:         .init_array
-      Size:            0x0000000000000008
+#    - Name:            init_array
+#      Type:            STT_OBJECT
+#      Section:         .init_array
+#      Size:            0x0000000000000008
     - Name:            .text
       Type:            STT_SECTION
       Section:         .text
     - Name:            .data
       Type:            STT_SECTION
       Section:         .data
     - Name:            .bss
       Type:            STT_SECTION
       Section:         .bss
-    - Name:            .init_array
-      Type:            STT_SECTION
-      Section:         .init_array
+#    - Name:            .init_array
+#      Type:            STT_SECTION
+#      Section:         .init_array
     - Name:            .comment
       Type:            STT_SECTION
       Section:         .comment
     - Name:            .note.GNU-stack
       Type:            STT_SECTION
       Section:         .note.GNU-stack
     - Name:            .eh_frame
       Type:            STT_SECTION
       Section:         .eh_frame
   Global:
     - Name:            main
       Type:            STT_FUNC
       Section:         .text
       Size:            0x0000000000000012
 ...