[Bug ld/20989] Every 64-bit Solaris 12/SPARC executable dies with SIGILL

[ro at CeBiTec dot Uni-Bielefeld.DE]

https://sourceware.org/bugzilla/show_bug.cgi?id=20989

--- Comment #2 from Rainer Orth <ro at CeBiTec dot Uni-Bielefeld.DE> ---
> --- Comment #1 from Alan Modra <amodra at gmail dot com> ---
> How is crt1.o testing that __start_crt_compiler is undefined?  I'm talking
> about an "if (foo)" test used in a call to a weak function:
>   if (foo)
>     foo ();

You've got this (I'm attaching both the crt1.o and empty-ld and
empty-gld executables for reference) in crt1.o:

crt1.o:

cc  __start_crt+0x4c:       2f 00 00 00  sethi     %hi(0x0), %l7
d0  __start_crt+0x50:       f4 74 60 00  stx       %i2, [%l1]
d4  __start_crt+0x54:       ac 1d e0 00  xor       %l7, 0x0, %l6
d8  __start_crt+0x58:       ea 5c 00 16  ldx       [%l0 + %l6], %l5
dc  __start_crt+0x5c:       02 c5 40 09  brz,pn    %l5, +0x24   
<__start_crt+0x80>

^ offsets (in hex) from the beginning of .text to allow matching with
  the relocs below.

  This is the

  if (__start_crt_compiler)
    __start_crt_compiler ();

  part ...

e0  __start_crt+0x60:       91 3e 20 00  sra       %i0, 0x0, %o0
e4  __start_crt+0x64:       40 00 00 00  call      +0x0         
<__start_crt+0x64>

  ... and here are the corresponding relocs.

   [17]  R_SPARC_GOTDATA_OP_HIX22    0xcc     0      0  .text    
__start_crt_compiler
   [18]  R_SPARC_GOTDATA_OP_LOX10    0xd4     0      0  .text    
__start_crt_compiler
   [19]  R_SPARC_GOTDATA_OP          0xd8     0      0  .text    
__start_crt_compiler
   [20]  R_SPARC_WPLT30              0xe4     0      0  .text    
__start_crt_compiler

When single-stepping through this part of empty-ld (ld output), I find:

    __start_crt+0x4c:       2f 00 00 00  sethi     %hi(0x0), %l7
    __start_crt+0x50:       f4 74 60 00  stx       %i2, [%l1]
    __start_crt+0x54:       ac 1d e0 08  xor       %l7, 0x8, %l6
    __start_crt+0x58:       ea 5c 00 16  ldx       [%l0 + %l6], %l5
    __start_crt+0x5c:       02 c5 40 09  brz,pn    %l5, +0x24   
<__start_crt+0x80>
    __start_crt+0x60:       91 3e 20 00  sra       %i0, 0x0, %o0
    __start_crt+0x64:       40 00 00 00  call      +0x0         
<__start_crt+0x64>

__start_crt+0x48:        brnz,pn   %l2, 0x100000b94 <__start_crt+0x54>

(gdb) p/x $l2
$5 = 0xffffffff7ffffb08

__start_crt+0x4c:        sethi  %hi(0), %l7
__start_crt+0x54:        xor  %l7, 8, %l6
__start_crt+0x58:        ldx  [ %l0 + %l6 ], %l5
__start_crt+0x5c:        brz,pn   %l5, 0x100000bc0 <__start_crt+0x80>

(gdb) p/x $l5
$4 = 0x0

  I.e. __start_crt_compiler is 0 and the branch is taken, skipping the
  call.

__start_crt+0x60:        sra  %i0, 0, %o0
__start_crt+0x80:        sethi  %hi(0x100000), %i3

On the other hand, with the gld-produced executable, I get

    __start_crt+0x4c:       2f 00 04 02  sethi     %hi(0x100800), %l7
    __start_crt+0x50:       f4 74 60 00  stx       %i2, [%l1]
    __start_crt+0x54:       ac 1d fd f0  xor       %l7, -0x210, %l6
    __start_crt+0x58:       aa 04 00 16  add       %l0, %l6, %l5
    __start_crt+0x5c:       02 c5 40 09  brz,pn    %l5, +0x24   
<__start_crt+0x80>
    __start_crt+0x60:       91 3e 20 00  sra       %i0, 0x0, %o0
    __start_crt+0x64:       7f ff fe 57  call      -0x6a4        <0x100000000>

__start_crt+0x48:        brnz,pn   %l2, 0x100000694 <__start_crt+0x54>

(gdb) p/x $l2
$4 = 0xffffffff7ffff9d8

__start_crt+0x4c:        sethi  %hi(0x100800), %l7
__start_crt+0x54:        xor  %l7, -528, %l6
__start_crt+0x58:        add  %l0, %l6, %l5
__start_crt+0x5c:        brz,pn   %l5, 0x1000006c0 <__start_crt+0x80>

(gdb) p/x $l5
$6 = 0x100000000

__start_crt+0x60:        sra  %i0, 0, %o0
__start_crt+0x64:        call  0x100000000

  I.e. __start_crt_compiler is non-NULL, the call is taken, but the
  destination is invalid, leading to the SIGILL.

        Rainer

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