[GHC] #12147: GHC's Linker Should Support Relocation Type 42

[GHC]

#12147: GHC's Linker Should Support Relocation Type 42
-------------------------------------+-------------------------------------
        Reporter:  gershomb          |                Owner:  Phyx-
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.0.2
       Component:  Runtime System    |              Version:  8.0.1
  (Linker)                           |
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2303
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Phyx-):

 I haven't written a testcase since you need `binutils-2.26` for it to
 trigger and I don't think I can force the test only then.

 In any case, simplest case to reproduce this is to compile `GHC` with
 `DYNAMIC_GHC_PROGRAMS=NO`

 I use this assembly file as input:


 {{{
 # x86_64
 # as as_test.s -o as_test.o && objdump -Dr as_test.o
 # ghc --interactive hs_test as_test.o

 .text
 .globl foo

 foo:
         push %rbp
         mov %rsp, %rbp

         mov msg at GOTPCREL(%rip), %rdi
         call puts at PLT

         pop %rbp
         ret

 .data
 msg:
         .ascii "Hello World!\0"
         len = . - msg
 }}}

 Which with
 {{{
 [phyx at localhost ~]$ as --version
 GNU assembler (GNU Binutils) 2.26.20160125
 }}}

 returns the expected relocation

 {{{
 [phyx at localhost ~]$ as as_test.s -o as_test.o && objdump -Dr as_test.o

 as_test.o:     file format elf64-x86-64


 Disassembly of section .text:

 0000000000000000 <foo>:
    0:   55                      push   %rbp
    1:   48 89 e5                mov    %rsp,%rbp
    4:   48 8b 3d 00 00 00 00    mov    0x0(%rip),%rdi        # b <foo+0xb>
                         7: R_X86_64_REX_GOTPCRELX       msg-0x4
    b:   e8 00 00 00 00          callq  10 <foo+0x10>
                         c: R_X86_64_PLT32       puts-0x4
   10:   5d                      pop    %rbp
   11:   c3                      retq

 Disassembly of section .data:

 0000000000000000 <msg>:
    0:   48                      rex.W
    1:   65 6c                   gs insb (%dx),%es:(%rdi)
    3:   6c                      insb   (%dx),%es:(%rdi)
    4:   6f                      outsl  %ds:(%rsi),(%dx)
    5:   20 57 6f                and    %dl,0x6f(%rdi)
    8:   72 6c                   jb     76 <len+0x69>
    a:   64 21 00                and    %eax,%fs:(%rax)
 }}}

 Before the patch it crashes as expected

 {{{
 [phyx at localhost ~]$ ghc/inplace/bin/ghc-stage2 --interactive as_test.o
 hs_test.hs
 GHCi, version 8.1.20160604: http://www.haskell.org/ghc/  :? for help
 ghc-stage2: as_test.o: unhandled ELF relocation(RelA) type 42

 linking extra libraries/objects failed
 }}}

 And after the patch

 {{{
 GHCi, version 8.1.20160604: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( hs_test.hs, interpreted )
 Ok, modules loaded: Main.
 *Main> main
 Hello World!
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12147#comment:7>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler