[LLVMbugs] [Bug 12851] New: clang generates relocs using discard-able symbols

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12851

             Bug #: 12851
           Summary: clang generates relocs using discard-able symbols
           Product: new-bugs
           Version: trunk
          Platform: Sun
        OS/Version: Solaris
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sbn at tbricks.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Hello!

I faced the following problem with clang and Solaris linker when building code
that contains COMDAT groups with section containing template function
instantiations.

$ cat -n a.cpp
      1  #include "a.h"
      2
      3  void baz()
      4  {
      5      bar(10);
      6  }
$ cat -n b.cpp
      1  #include "a.h"
      2
      3  void foo()
      4  {
      5      bar(12);
      6  }
$ cat -n a.h
      1  struct S
      2  {
      3      ~S();
      4  };
      5
      6  template<typename T>
      7  int bar(T t)
      8  {
      9      S s;
     10      return t*3;
     11  }
$ /opt/clang/bin/clang++ -c a.cpp
$ /opt/clang/bin/clang++ -c b.cpp
$ elfdump -c a.o | grep ^Section
Section Header[1]:  sh_name: .group
Section Header[2]:  sh_name: .text
Section Header[3]:  sh_name: .rel.text
Section Header[4]:  sh_name: .data
Section Header[5]:  sh_name: .bss
Section Header[6]:  sh_name: .text._Z3barIiEiT_
Section Header[7]:  sh_name: .rel.text._Z3barIiEiT_
Section Header[8]:  sh_name: .note.GNU-stack
Section Header[9]:  sh_name: .eh_frame
Section Header[10]:  sh_name: .rel.eh_frame
Section Header[11]:  sh_name: .shstrtab
Section Header[12]:  sh_name: .symtab
Section Header[13]:  sh_name: .strtab
$ elfdump -g a.o

Group Section:  .group
      index    flags / section         signature symbol
        [0]   [ COMDAT ]               _Z3barIiEiT_
        [1]   .text._Z3barIiEiT_ [6]
$ ld -Dsections -r -o all.o a.o b.o
debug:
debug: Solaris Linkers: 5.10-1.1505
debug:
debug: section=[1].group; input from file=a.o
debug: section=[1].group; input from file=a.o; defines COMDAT group: 
signature symbol: _Z3barIiEiT_
debug: section=.group; added to segment=extra (created)
...
debug: section=[6].text._Z3barIiEiT_; input from file=a.o
debug: section=[6].text._Z3barIiEiT_; input from file=a.o; member of 
COMDAT group: signature symbol: _Z3barIiEiT_
debug: section=.text._Z3barIiEiT_; added to segment=text (created)
...
debug: section=[9].eh_frame; input from file=a.o
debug: section=.eh_frame; added to segment=data (created)
...
debug: section=[1].group; input from file=b.o
debug: section=[1].group; input from file=b.o; defines COMDAT group: 
signature symbol: _Z3barIiEiT_
debug: section=[1].group; input from file=b.o; discarded in favor of 
group: signature symbol: _Z3barIiEiT_: file=a.o
...
debug: section=[6].text._Z3barIiEiT_; input from file=b.o
debug: section=[6].text._Z3barIiEiT_; input from file=b.o; member of 
COMDAT group: signature symbol: _Z3barIiEiT_
debug: section=[6].text._Z3barIiEiT_; input from file=b.o; discarded in 
favor of group: signature symbol: _Z3barIiEiT_: file=a.o
...
debug: section=[9].eh_frame; input from file=b.o
debug: section=.eh_frame; added to segment=data
debug:
ld: fatal: relocation error: R_386_32: file b.o: section 
[10].rel.eh_frame: symbol .text._Z3barIiEiT_ (section): symbol has been 
discarded with discarded section: [6].text._Z3barIiEiT_

So the linker successfully discarded .text._Z3barIiEiT_ in b.o in favor 
of the one in a.o

But it got problems when processing relocations for .eh_frame section in b.o

$ elfdump -r -N .rel.eh_frame b.o
Relocation Section:  .rel.eh_frame
     type                       offset             section        symbol
   R_386_32                       0x20             .rel.eh_frame  .text 
(section)
   R_386_32                       0x3c             .rel.eh_frame  
.text._Z3barIiEiT_ (section)

$ dump -r b.o
b.o:
     **** RELOCATION INFORMATION ****
...
.rel.eh_frame:
Offset      Symndx              Type
0x20        2                   1
0x3c        5                   1

$ elfdump -l -s b.o

Symbol Table Section:  .symtab
      index    value      size      type bind oth ver shndx / name
        [0]  0x00000000 0x00000000  NOTY LOCL  D    0 UNDEF
        [1]  0x00000000 0x00000000  FILE LOCL  D    0 ABS            b.cpp
        [2]  0x00000000 0x00000000  SECT LOCL  D    0 .text
        [3]  0x00000000 0x00000000  SECT LOCL  D    0 .data
        [4]  0x00000000 0x00000000  SECT LOCL  D    0 .bss
        [5]  0x00000000 0x00000000  SECT LOCL  D    0 .text._Z3barIiEiT_
        [6]  0x00000000 0x00000000  SECT LOCL  D    0 .note.GNU-stack
        [7]  0x00000000 0x00000000  SECT LOCL  D    0 .eh_frame
        [8]  0x00000000 0x00000000  SECT LOCL  D    0 .group
        [9]  0x00000000 0x00000030  FUNC WEAK  D    0 .text._Z3barIiEiT_ 
_Z3barIiEiT_
       [10]  0x00000000 0x00000022  FUNC GLOB  D    0 .text          _Z3foov
       [11]  0x00000000 0x00000000  NOTY GLOB  D    0 UNDEF          
_ZN1SD1Ev

The second relocation entry in .rel.eh_frame references section symbol 
[5].text._Z3barIiEiT_ which is LOCAL and thus is discarded with 
discarded section .text._Z3barIiEiT_

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