[llvm-objcopy] Implement support for section groups

This diff adds support for SHT_GROUP sections to llvm-objcopy.
Some sections are interrelated and comprise a group.
For example, a definition of an inline function might require, 
in addition to the section containing its instructions, 
a read-only data section containing literals referenced inside the function.
A section of the type SHT_GROUP contains the indices of the group members,
therefore, it needs to be updated whenever the indices change.
Similarly, the fields sh_link, sh_info should be recalculated as well.

[Resubmit r328012 with the proper handling of endianness]

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D43996

llvm-svn: 328143

1 files changed, 56 insertions, 0 deletions

diff --git a/llvm/test/tools/llvm-objcopy/group-big-endian.test b/llvm/test/tools/llvm-objcopy/group-big-endian.test
new file mode 100644
index 00000000000..d5a02607113
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/group-big-endian.test
@@ -0,0 +1,56 @@
+# RUN: yaml2obj %s > %t
+# RUN: llvm-objcopy -remove-section=.text.bar %t %t2
+# RUN: llvm-readobj -elf-section-groups %t2 | FileCheck %s
+
+# In this test the section .text.bar is getting removed, as a result, 
+# the indices of the sections which go after .text.bar will change, 
+# thus the fields Link, Info and the content of .group should be updated.
+
+# CHECK:           Name: .group
+# CHECK-NEXT:      Index: 1
+# CHECK-NEXT:      Link: 3
+# CHECK-NEXT:      Info: 2
+# CHECK-NEXT:      Type: COMDAT (0x1)
+# CHECK-NEXT:      Signature: foo
+# CHECK:           .text.foo (2)
+
+--- !ELF
+FileHeader:      
+  Class:           ELFCLASS64
+  Data:            ELFDATA2MSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:        
+  - Name:            .group
+    Type:            SHT_GROUP
+    Link:            .symtab
+    AddressAlign:    0x0000000000000004
+    Info:            foo
+    Members:         
+      - SectionOrType:   GRP_COMDAT
+      - SectionOrType:   .text.foo
+  - Name:            .text.bar
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000010
+  - Name:            .text.foo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR, SHF_GROUP ]
+    AddressAlign:    0x0000000000000010
+Symbols:
+  Local:           
+    - Name:            .text.bar
+      Type:            STT_SECTION
+      Section:         .text.bar
+    - Name:            .text.foo
+      Type:            STT_SECTION
+      Section:         .text.foo         
+  Weak:            
+    - Name:            bar
+      Type:            STT_FUNC
+      Section:         .text.bar
+      Size:            0x0000000000000000
+    - Name:            foo
+      Type:            STT_FUNC
+      Section:         .text.foo
+      Size:            0x0000000000000000