suspect assembly code for gcc 2.95.3 for ppc

["Bob Boz" <gcc_compiler at yahoo dot ca>]

I have noticed there's been a few problems with variable args and ppc in the
past. I wonder if this one is another case?
This seems to be a problem with va_list, var_arg handing.
Here's the function that uses them and the assembly produced below:

unsigned
foo(unsigned start, ...)
{
    /* ... */
    va_list args;
    /* ... */
    va_start(args, start);
    for(;;) {
 name = va_arg(args, char *);
 if(name == NULL) break;
 /* ... */
    }
    va_end(args);
    /* ... */
}

edited assembly:

foo:
  a0:   94 21 ff 50     stwu    r1,-176(r1)
  a4:   7c 08 02 a6     mflr    r0
  a8:   93 61 00 9c     stw     r27,156(r1)
  ac:   93 81 00 a0     stw     r28,160(r1)
  b0:   93 a1 00 a4     stw     r29,164(r1)
  b4:   93 c1 00 a8     stw     r30,168(r1)
  b8:   93 e1 00 ac     stw     r31,172(r1)
  bc:   90 01 00 b4     stw     r0,180(r1)
  c0:   7c 3f 0b 78     mr      r31,r1

  c4:   3c 00 01 00     lis     r0,256
  c8:   90 9f 00 0c     stw     r4,12(r31)    <====

  cc:   3b 80 00 00     li      r28,0

  d0:   90 1f 00 80     stw     r0,128(r31)
  d4:   39 7f 00 b8     addi    r11,r31,184
  d8:   38 9f 00 08     addi    r4,r31,8

  dc:   3b bf 00 01     addi    r29,r31,1     <====
  e0:   38 1f 00 80     addi    r0,r31,128

  e4:   91 7f 00 84     stw     r11,132(r31)
  e8:   90 9f 00 88     stw     r4,136(r31)
  ec:   7c 7b 1b 78     mr      r27,r3
  f0:   90 bf 00 10     stw     r5,16(r31)
  f4:   90 df 00 14     stw     r6,20(r31)
  f8:   90 ff 00 18     stw     r7,24(r31)
  fc:   91 1f 00 1c     stw     r8,28(r31)
 100:   91 3f 00 20     stw     r9,32(r31)
 104:   91 5f 00 24     stw     r10,36(r31)
 108:   93 bf 00 78     stw     r29,120(r31)
 10c:   90 1f 00 74     stw     r0,116(r31)
 110:   9b 9f 00 70     stb     r28,112(r31)
 114:   9b 9f 00 71     stb     r28,113(r31)

112(r31) is address of "gpr" in args (va_list data structure)
113(r31) is address of "fpr" in args (va_list data structure)
116(r31) is address of "overflow_arg_area" in args (va_list data
structure)
120(r31) is address of "reg_save_area" in args (va_list data structure)

fpr and gpr are set to 0 (r28) -> this does not reflect the comment of
the va_list data structure for PPC (but it works) since the first
register used for the va_list is r4.

overflow_arg_area is set to (r31 + 128) -> i do not know if this value
is correct, but there is something funny with this value since we save
256 in the address 128(r31).
could anyone give us more info about it since we were expecting
something different as an address on the stack?

reg_save_area is set to (r31 + 1), but should be set to (r31 + 12) since
the first register used for the "..." arguments is r4 and since r4 is
saved into memory at the address 12(r31). Due to this "error", we read
something that is not aligned and we read a bad value.

Replacing the 1 to a 12 by hand for this function seems to solve the
problem.

-B