ELF: Handle sh_addralign being set to zero

sh_addralign of zero is equivalent to sh_addralign of one, meaning
no alignment specified. Avoid calculating Log2 or modulus when
sh_addralign is zero as the results will not be useful.

llvm-svn: 226572

lld/lib/ReaderWriter/ELF/Atoms.h

@@ -286,6 +286,9 @@ public:
     if ((_symbol->getType() == llvm::ELF::STT_COMMON) ||
         _symbol->st_shndx == llvm::ELF::SHN_COMMON) {
       return Alignment(llvm::Log2_64(_symbol->st_value));
+    } else if (_section->sh_addralign == 0) {
+      // sh_addralign of 0 means no alignment
+      return Alignment(0, _symbol->st_value);
     }
     return Alignment(llvm::Log2_64(_section->sh_addralign),
                      _symbol->st_value % _section->sh_addralign);

lld/test/elf/sh_addralign.test

@@ -0,0 +1,38 @@
+# Check handling of section alignment.
+# RUN: yaml2obj -format=elf %s > %t-obj
+# RUN: lld -flavor gnu -target arm64 -o %t-exe %t-obj
+# RUN: llvm-objdump -h %t-exe | FileCheck %s
+
+# CHECK: 8 .data         00000000 0000000000402000 DATA
+
+!ELF
+FileHeader: !FileHeader
+  Class: ELFCLASS64
+  Data: ELFDATA2LSB
+  Type: ET_REL
+  Machine: EM_AARCH64
+
+Sections:
+- Name: .text
+  Type: SHT_PROGBITS
+  Content: ''
+  AddressAlign: 0
+  Flags: [SHF_ALLOC, SHF_EXECINSTR]
+- Name:            .bss
+  Type:            SHT_NOBITS
+  Flags:           [ SHF_WRITE, SHF_ALLOC ]
+  AddressAlign:    1
+  Content:         ''
+  Size:            0x80000000
+- Name: .data
+  Type: SHT_PROGBITS
+  Content: ''
+  AddressAlign: 4096
+  Flags: [SHF_ALLOC, SHF_WRITE]
+
+Symbols:
+  Global:
+    - Name: _start
+      Section: .text
+      Value: 0x0
+      Size: 4