[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.

Test plan: make check-all

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

llvm-svn: 328012

4 files changed, 152 insertions, 0 deletions

diff --git a/llvm/test/tools/llvm-objcopy/Inputs/groups.o b/llvm/test/tools/llvm-objcopy/Inputs/groups.o
new file mode 100644
index 00000000000..e92b98046a3
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/Inputs/groups.o
diff --git a/llvm/test/tools/llvm-objcopy/group-unchanged.test b/llvm/test/tools/llvm-objcopy/group-unchanged.test
new file mode 100644
index 00000000000..9e86172bad5
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/group-unchanged.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, since this section
+# goes after all the sections comprising a group, the content of the
+# section .group doesn't change.
+
+# 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:            ELFDATA2LSB
+  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.foo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR, SHF_GROUP ]
+    AddressAlign:    0x0000000000000010
+  - Name:            .text.bar
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000010
+Symbols:
+  Local:           
+    - Name:            .text.foo
+      Type:            STT_SECTION
+      Section:         .text.foo         
+    - Name:            .text.bar
+      Type:            STT_SECTION
+      Section:         .text.bar
+  Weak:            
+    - Name:            foo
+      Type:            STT_FUNC
+      Section:         .text.foo
+      Size:            0x0000000000000000
+    - Name:            bar
+      Type:            STT_FUNC
+      Section:         .text.bar
+      Size:            0x0000000000000000
diff --git a/llvm/test/tools/llvm-objcopy/group.test b/llvm/test/tools/llvm-objcopy/group.test
new file mode 100644
index 00000000000..4023f1228f0
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/group.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:            ELFDATA2LSB
+  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
diff --git a/llvm/test/tools/llvm-objcopy/strip-dwo-groups.test b/llvm/test/tools/llvm-objcopy/strip-dwo-groups.test
new file mode 100644
index 00000000000..957bb553b72
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/strip-dwo-groups.test
@@ -0,0 +1,40 @@
+# RUN: cp %p/Inputs/groups.o %t
+# RUN: llvm-objcopy -strip-dwo %t
+# RUN: llvm-readobj -elf-section-groups %t | FileCheck %s
+
+// Source code of groups.o:
+//
+// template <class T>
+// struct S {
+//    static constexpr T X = T(1);
+//    T getX() { return X; }
+// };
+// void f() {
+//  S<int> A;
+//  S<double> B;
+//  int a = A.getX();
+//  int b = B.getX();
+// }
+//
+// clang -g -gsplit-dwarf -std=c++11 -c groups.cpp -o groups.o
+
+// `llvm-objcopy -strip-dwo` strips out dwo sections, as a result, the index of 
+// the symbol table, the indices of the symbols and the indices of the sections 
+// which go after the removed ones will change. Consequently, the fields 
+// Link, Info and the content of .group need to be updated. In the past 
+// `llvm-objcopy -strip-dwo` used to produce invalid binaries with 
+// broken .group section, this test verifies the correctness of 
+// Link, Info and the content of this section.
+
+CHECK:          Name: .group (179)
+CHECK-NEXT:     Index: 17
+CHECK-NEXT:     Link: 19
+CHECK-NEXT:     Info: 14
+CHECK:          .text._ZN1SIiE4getXEv (2)
+
+CHECK:          Name: .group (179)
+CHECK-NEXT:     Index: 18
+CHECK-NEXT:     Link: 19
+CHECK-NEXT:     Info: 13
+CHECK:          .text._ZN1SIdE4getXEv (4)
+CHECK-NEXT:     .rela.text._ZN1SIdE4getXEv (21)