[lld] r295067 - [ELF] - Do not segfault when using -r and section groups.

[George Rimar via llvm-commits]

Author: grimar
Date: Tue Feb 14 10:42:38 2017
New Revision: 295067

URL: http://llvm.org/viewvc/llvm-project?rev=295067&view=rev
Log:
[ELF] - Do not segfault when using -r and section groups.

If we had SHT_GROUP sections, then when -r was used we might crash.
This is PR31952.

Issue happened because we emited relocation section though its target was discared
because was a member of duplicated group. When we tried to get VA of target,
segfault happened.
Core cause is the bug that GNU as 2.27 (and probably later versions) has.
In compare with llvm-mc, it does not include relocation sections into the group, 
like shown in testcase. This patch covers that case.

Differential revision: https://reviews.llvm.org/D29929

Added:
    lld/trunk/test/ELF/relocation-group.test
Modified:
    lld/trunk/ELF/InputFiles.cpp

Modified: lld/trunk/ELF/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.cpp?rev=295067&r1=295066&r2=295067&view=diff
==============================================================================
--- lld/trunk/ELF/InputFiles.cpp (original)
+++ lld/trunk/ELF/InputFiles.cpp Tue Feb 14 10:42:38 2017
@@ -367,17 +367,20 @@ elf::ObjectFile<ELFT>::createInputSectio
     return &InputSection<ELFT>::Discarded;
   case SHT_RELA:
   case SHT_REL: {
+    // Find the relocation target section and associate this
+    // section with it. Target can be discarded, for example
+    // if it is a duplicated member of SHT_GROUP section, we
+    // do not create or proccess relocatable sections then.
+    InputSectionBase<ELFT> *Target = getRelocTarget(Sec);
+    if (!Target)
+      return nullptr;
+
     // This section contains relocation information.
     // If -r is given, we do not interpret or apply relocation
     // but just copy relocation sections to output.
     if (Config->Relocatable)
       return make<InputSection<ELFT>>(this, &Sec, Name);
 
-    // Find the relocation target section and associate this
-    // section with it.
-    InputSectionBase<ELFT> *Target = getRelocTarget(Sec);
-    if (!Target)
-      return nullptr;
     if (Target->FirstRelocation)
       fatal(toString(this) +
             ": multiple relocation sections to one section are not supported");

Added: lld/trunk/test/ELF/relocation-group.test
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/relocation-group.test?rev=295067&view=auto
==============================================================================
--- lld/trunk/test/ELF/relocation-group.test (added)
+++ lld/trunk/test/ELF/relocation-group.test Tue Feb 14 10:42:38 2017
@@ -0,0 +1,43 @@
+# RUN: yaml2obj %s -o %t.o
+# RUN: ld.lld %t.o %t.o -o %t -r
+# RUN: llvm-readobj -s %t.o | FileCheck %s
+
+# CHECK:     Name: .text.foo
+# CHECK:     Name: .rela.text.foo
+
+## YAML below corresponds to following asm code:
+## .section .text,"axG", at progbits,foo,comdat
+## .quad bar
+## gas 2.27 does not include .rela.text to group in that case:
+## COMDAT group section [    1] `.group' [foo] contains 1 sections:
+##   [Index]    Name
+##   [    5]   .text
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .group
+    Type:            SHT_GROUP
+    Link:            .symtab
+    Info:            foo
+    Members:
+      - SectionOrType:    GRP_COMDAT
+      - SectionOrType:    .text.foo
+  - Name:            .text.foo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR, SHF_GROUP ]
+  - Name:            .rela.text.foo
+    Type:            SHT_RELA
+    Flags:           [ SHF_INFO_LINK ]
+    Link:            .symtab
+    Info:            .text.foo
+    Relocations:
+      - Offset:          0x0000000000000000
+        Symbol:          foo
+        Type:            R_X86_64_64
+Symbols:
+  Global:
+    - Name:            foo