[llvm-objcopy] - Report SHT_GROUP sections with invalid alignment.

This patch fixes the reason of ubsan failure (UB detected) 
happened after landing the D59638 (I had to revert it).
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap-ubsan/builds/11760/steps/check-llvm%20ubsan/logs/stdio)

Problem is the following. Our implementation of GroupSection assumes that
its address is 4 bytes aligned when writes it:

template <class ELFT>
void ELFSectionWriter<ELFT>::visit(const GroupSection &Sec) {
  ELF::Elf32_Word *Buf =
      reinterpret_cast<ELF::Elf32_Word *>(Out.getBufferStart() + Sec.Offset);
...

But the test case for D59638 did not set AddressAlign in YAML. So address was
not 4 bytes aligned since Sec.Offset was odd. That triggered the issue.

This patch teaches llvm-objcopy to report an error for such sections (which should
not met in reality), what is better than having UB.

Differential revision: https://reviews.llvm.org/D59695

llvm-svn: 356853

llvm/test/tools/llvm-objcopy/ELF/group-addr-misaligned.test

@@ -0,0 +1,38 @@
+# RUN: yaml2obj %s > %t
+# RUN: not llvm-objcopy %t %t2 2>&1 | FileCheck %s
+# CHECK: error: Invalid alignment 1 of group section .group.
+
+# In this test, we check that llvm-objcopy reports an error
+# for SHT_GROUP section with invalid alignment (not a multiple of 4). 
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+## It is not important for passing the test case to have this placeholder,
+## but having it would trigger ubsan failure when writing the group section
+## into a file if the error tested would not be reported by llvm-objcopy.
+  - Name:            .placeholder
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000001
+    Content:         "00"
+  - Name:            .group
+    Type:            SHT_GROUP
+    Link:            .symtab
+    AddressAlign:    0x0000000000000001
+    Info:            foo
+    Members:
+      - SectionOrType:   GRP_COMDAT
+      - SectionOrType:   .text.foo
+  - Name:            .text.foo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR, SHF_GROUP ]
+    AddressAlign:    0x0000000000000001
+Symbols:
+  Local:
+    - Name:            foo
+      Section:         .group

llvm/tools/llvm-objcopy/ELF/Object.cpp

@@ -949,6 +949,9 @@ template <class ELFT> void ELFBuilder<ELFT>::readProgramHeaders() {
 
 template <class ELFT>
 void ELFBuilder<ELFT>::initGroupSection(GroupSection *GroupSec) {
+  if (GroupSec->Align % sizeof(ELF::Elf32_Word) != 0)
+    error("Invalid alignment " + Twine(GroupSec->Align) + " of group section " +
+          GroupSec->Name);
   auto SecTable = Obj.sections();
   auto SymTab = SecTable.template getSectionOfType<SymbolTableSection>(
       GroupSec->Link,