ppc32: Building tiny executable

[Mathieu Malaterre]

On Fri, May 4, 2018 at 2:42 PM, Mathieu Malaterre
<mathieu.malaterre@gmail.com> wrote:
> On Fri, May 4, 2018 at 2:40 PM, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
>> On Fri, May 04, 2018 at 02:23:02PM +0200, Mathieu Malaterre wrote:
>>> On Fri, May 4, 2018 at 2:16 PM, Segher Boessenkool
>>> <segher@kernel.crashing.org> wrote:
>>> > On Fri, May 04, 2018 at 01:45:35PM +0200, Mathieu Malaterre wrote:
>>> >> $ gcc -static -ffreestanding -nostartfiles  -s -o tiny tiny.c
>>> >> $ ./tiny
>>> >> Segmentation fault
>>> >>
>>> >> What do I need to pay attention to on ppc to build tiny executable
>>> >> using the _start function ?
>>> >
>>> > You need to set up r13.  This is powerpc64?  (32-bit works fine for me,
>>> > but you may be using a different ABI, you didn't tell.  I'm on Linux).
>>>
>>> Nope, ppc32.
>>>
>>> $ objdump -f tiny
>>>
>>> tiny:     file format elf32-powerpc
>>> architecture: powerpc:common, flags 0x00000102:
>>> EXEC_P, D_PAGED
>>> start address 0x10000120
>>>
>>> dmesg states:
>>>
>>> [ 1552.267961] tiny[2127]: unhandled signal 11 at ffff8fd0 nip
>>> 10000180 lr 10000150 code 1
>>
>> So
>>
>> $ gdb ./tiny
>> (gdb) run
>> (gdb) disas
>>
>> and look what line the "=>" mark is on.
>
> (gdb) r
> Starting program: /tmp/tiny
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x10000180 in ?? ()
> (gdb) disas
> No function contains program counter for selected frame.
> (gdb)

Tried again without -s command line option:

Program received signal SIGSEGV, Segmentation fault.
0x10000180 in _exit ()
(gdb) disas
Dump of assembler code for function _exit:
   0x10000150 <+0>: stwu    r1,-32(r1)
   0x10000154 <+4>: stw     r29,20(r1)
   0x10000158 <+8>: lis     r29,4098
   0x1000015c <+12>: addi    r29,r29,-12
   0x10000160 <+16>: stw     r30,24(r1)
   0x10000164 <+20>: addis   r29,r2,0
   0x10000168 <+24>: stw     r31,28(r1)
   0x1000016c <+28>: li      r30,49
   0x10000170 <+32>: mr      r31,r3
   0x10000174 <+36>: addi    r29,r29,-28672
   0x10000178 <+40>: nop
   0x1000017c <+44>: nop
=> 0x10000180 <+48>: lwz     r9,-28720(r2)
   0x10000184 <+52>: li      r0,234
   0x10000188 <+56>: mr      r3,r31