[llvm-dev] POssible bug in the Arm code generator

[Erik de Castro Lopo via llvm-dev]

Owen Shepherd wrote:

> Pay closer attention to the instruction descriptions on the page you linked
> above:
> 
> LDR{*type*}{*cond*} *Rt*, [*Rn* {, #*offset*}]        ; immediate offset
> 
> LDR{*type*}{*cond*} *Rt*, [*Rn*, #*offset*]!          ; pre-indexed
> 
> 
> The pre-indexed form is always specified with an offset, and* follows the
> brackets with an exclamation mark*. You have an immediate offset load, for
> which Rt==Rn is permitted.

Ah, missed that.

> A possible reason for an illegal instruction exception is that you have
> generated some ARM code and tried to execute it as Thumb or vise-versa.

Well, I'm getting SIGILL, but GHC does not generate or use thumb instructions
and the SIGILL happens after susccessfuly running a bunch of other arm
instructions. From GDB:

  Program received signal SIGILL, Illegal instruction.
  0x03ff9dbc in stg_ap_v_fast ()
  (gdb) bt
  #0  0x03ff9dbc in stg_ap_v_fast ()
  #1  0x03fc6ce6 in StgRun (f=0x3ff9db4 <stg_ap_v_fast>, basereg=0x49d2090 <MainCapability+16>) at
      rts/StgCRun.c:81
  #2  0x03fca52a in schedule (initialCapability=0x49d2080 <MainCapability>, task=0x49e62c0) at 
      rts/Schedule.c:524
  #3  0x03fcc5e6 in scheduleWaitThread (tso=0xb6c07000, ret=0x0, pcap=0xbeffeb74) at 
      rts/Schedule.c:2429
  #4  0x03fbc7e4 in rts_evalLazyIO (cap=0xbeffeb74, p=0x402d470 <ZCMain_main_closure>, ret=0x0) at 
      rts/RtsAPI.c:500
  #5  0x03fce2be in hs_main (argc=3, argv=0xbeffed64, main_closure=0x402d470 <ZCMain_main_closure>, 
      rts_config=...) at rts/RtsMain.c:64
  #6  0x00141508 in main ()
  (gdb) disassemble
  Dump of assembler code for function stg_ap_v_fast:
     0x03ff9db4 <+0>:     push    {r7, lr}
     0x03ff9db6 <+2>:     sub     sp, #32
     0x03ff9db8 <+4>:     add     r7, sp, #0
     0x03ff9dba <+6>:     ldr     r3, [pc, #508]  ; (0x3ff9fb8 <stg_ap_v_fast+516>)
  => 0x03ff9dbc <+8>:     ldr     r3, [r3, #0]
     0x03ff9dbe <+10>:    and.w   r3, r3, #3


Erik
-- 
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Erik de Castro Lopo
http://www.mega-nerd.com/