Re: [GHC] #13617: GHCI Linker incorrectly handles the R_X86_64_PC32 relocation

9 Jul 2017

      #13617: GHCI Linker incorrectly handles the R_X86_64_PC32 relocation
--------------------------------+----------------------------------------
        Reporter:  RyanGlScott  |                Owner:  Phyx-
            Type:  bug          |               Status:  new
        Priority:  normal       |            Milestone:
       Component:  GHCi         |              Version:  8.0.2
      Resolution:               |             Keywords:
Operating System:  Windows      |         Architecture:  Unknown/Multiple
 Type of failure:  GHCi crash   |            Test Case:
      Blocked By:               |             Blocking:
 Related Tickets:  #7134        |  Differential Rev(s):
       Wiki Page:               |
--------------------------------+----------------------------------------

Comment (by Phyx-):

 It seems the code for `R_X86_64_PC32` does already make a trampoline,

 but only when the address is more than `32-bits` away:

 {{{
             case 4: /* R_X86_64_PC32 (ELF constant 2) -
 IMAGE_REL_AMD64_REL32 (PE constant 4) */
                {
                    intptr_t v;
                    v = ((intptr_t)S) + ((intptr_t)(int32_t)A) -
 ((intptr_t)pP) - 4;
                    if ((v >> 32) && ((-v) >> 32)) {
                        /* Make the trampoline then */
                        copyName ( getSymShortName (info, sym), strtab,
 symbol, 1000-1 );
                        S = makeSymbolExtra_PEi386(oc, symIndex, S, (char
 *)symbol);
                        /* And retry */
                        v = ((intptr_t)S) + ((intptr_t)(int32_t)A) -
 ((intptr_t)pP) - 4;
                        if ((v >> 32) && ((-v) >> 32)) {
                            barf("IMAGE_REL_AMD64_REL32: High bits are set
 in %zx for %s",
                                 v, (char *)symbol);
                        }
                    }
                    *(uint32_t *)pP = (uint32_t)v;
                    break;
                }
 }}}

 Which explains why it doesn't always segfault..

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13617#comment:3
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler