[LLD][ELF] Consolidate .ARM.extab.* sections into .ARM.extab

[peter.smith]

Summary

When -ffunction-sections and ARM C++ exceptions are used each .text.suffix section will have at least one .ARM.exidx.suffix section and may have an additional .ARM.extab.suffix section if the unwinding instructions are too large to inline into the .ARM.exidx table entry. For a large program without a linker script this can lead to a large number of section header table entries that can increase the size of the ELF file.

This change introduces a default rule for .ARM.extab.* to be placed in a single output section called .ARM.extab . This follows the behavior of ld.gold and ld.bfd.

fixes pr33407

[smeenai]

LGTM, but @ruiu or @rafael has to approve, of course. I'm happy to see this though :)

[ruiu]

LGTM

ELF/Writer.cpp

if (Name.startswith(".zdebug_"))
     return Saver.save("." + Name.substr(2));
 
   if (Config->Relocatable)
     return Name;
 
   for (StringRef V :
        {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
         ".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
-        ".gcc_except_table.", ".tdata.", ".ARM.exidx."}) {
+        ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."}) {
     StringRef Prefix = V.drop_back();
     if (Name.startswith(V) || Name == Prefix)
       return Prefix;
   }
 
   // CommonSection is identified as "COMMON" in linker scripts.
   // By default, it should go to .bss section.
   if (Name == "COMMON")

test/ELF/arm-exidx-canunwind.s

 // CHECK-NEXT:    11018:       1e ff 2f e1     bx      lr
 
 // CHECK-EXIDX: Contents of section .ARM.exidx:
 // 100d4 + f38 = 1100c = func1 (inline unwinding data)
 // 100dc + f34 = 11010 = func2 (100e0 + c = 100ec = .ARM.extab entry)
 // CHECK-EXIDX-NEXT: 100d4 380f0000 08849780 340f0000 0c000000
 // 100e4 + f30 = 11014 = terminate = func2 + sizeof(func2)
 // CHECK-EXIDX-NEXT: 100e4 300f0000 01000000
-// CHECK-EXIDX-NEXT: Contents of section .ARM.extab.text.func2:
+// CHECK-EXIDX-NEXT: Contents of section .ARM.extab:
 // 100ec + f28 = 11014 = __gxx_personality_v0
 // CHECK-EXIDX-NEXT: 100ec 280f0000 b0b0b000 00000000
 
 // CHECK-PT:          Name: .ARM.exidx
 // CHECK-PT-NEXT:     Type: SHT_ARM_EXIDX (0x70000001)
 // CHECK-PT-NEXT:     Flags [
 // CHECK-PT-NEXT:       SHF_ALLOC
 // CHECK-PT-NEXT:       SHF_LINK_ORDER

test/ELF/arm-exidx-gc.s

 // CHECK-NEXT:   11018:       1e ff 2f e1     bx      lr
 
 // GC should have removed table entries for unusedfunc1, unusedfunc2
 // and __gxx_personality_v1
 // CHECK-NOT: unusedfunc1
 // CHECK-NOT: unusedfunc2
 // CHECK-NOT: __gxx_personality_v1
 
-// CHECK-EXIDX-NOT: Contents of section .ARM.extab.text.unusedfunc2:
 // CHECK-EXIDX: Contents of section .ARM.exidx:
 // 100d4 + f38 = 1100c = func1
-// 100dc + f34 = 11010 = func2 (100e0 + 1c = 100fc = .ARM.extab.text.func2)
+// 100dc + f34 = 11010 = func2 (100e0 + 1c = 100fc = .ARM.extab)
 // CHECK-EXIDX-NEXT: 100d4 380f0000 08849780 340f0000 1c000000
 // 100e4 + f30 = 11014 = __gxx_personality_v0
 // 100ec + f2c = 11018 = __aeabi_unwind_cpp_pr0
 // CHECK-EXIDX-NEXT: 100e4 300f0000 01000000 2c0f0000 01000000
 // 100f4 + f28 = 1101c = __aeabi_unwind_cpp_pr0 + sizeof(__aeabi_unwind_cpp_pr0)
 // CHECK-EXIDX-NEXT: 100f4 280f0000 01000000
-// CHECK-EXIDX-NEXT: Contents of section .ARM.extab.text.func2:
+// CHECK-EXIDX-NEXT: Contents of section .ARM.extab:
 // 100fc + f18 = 11014 = __gxx_personality_v0
 // CHECK-EXIDX-NEXT: 100fc 180f0000 b0b0b000

test/ELF/arm-exidx-shared.s

  .global __aeabi_unwind_cpp_pr0
 __aeabi_unwind_cpp_pr0:
  bx lr
 
 // CHECK: Relocations [
 // CHECK-NEXT:   Section (6) .rel.plt {
 // CHECK-NEXT:     0x200C R_ARM_JUMP_SLOT __gxx_personality_v0
 
-// CHECK-EXTAB: Contents of section .ARM.extab.text.func2:
+// CHECK-EXTAB: Contents of section .ARM.extab:
 // 014c + 0ed8 = 0x1024 = __gxx_personality_v0(PLT)
 // CHECK-EXTAB-NEXT:  014c d80e0000 b0b0b000 00000000