RE: single stepping mips remote programs built with gcc 4.0

["Newman, Sarah R" <sarah.r.newman@lmco.com>]

> On Thu, Nov 17, 2005 at 02:23:17PM -0800, Newman, Sarah R wrote:
> > I built it with the default options, that good enough? 
> Something like
> > "-g -O2" it seems.
> > 
> > I doubt that mips32_next_pc is getting compiled in because 
> I can set a
> > breakpoint at mips_next_pc but not mips32_next_pc.  
> > mips_software_single_step never gets called in this 
> sequence, should it
> > be? 
> 
> Could you show me a session transcript?  If mips_software_single_step
> isn't placing the breakpoint, what is?
> 
> mips32_next_pc was probably inlined; you can retry with -g -O0 if you
> want.

mips32_next_pc is not being called.  

It seems that when gdb is single stepping at the source code level it
tries to skip over the function prologues (I could be wrong.)  I am
compiling with options "-g" and "-O2" and gcc 4.0 apparently removes the
prologues for very simple functions. I've been poking around
handle_inferior_event, mips_skip_prologue, and skip_prologue_using_sal
mostly.  I still think the very different assembly produced by gcc 4.0
is causing problems.  I may try comparing the 3.1 runtime behavior with
4.0 but I will have to recompile some libraries in order to do that and
it's late. :P  

Additionally, in the below source code, if you try to to do an assembly
listing within gdb of either function A or B, it shows the function
following within the disassembly.  IE disassembling function B displays
the code for A, and disassembling A displays the code for main, but main
is correctly displayed.

Some source code:

void b(int c){
  printf("%d",c+2);
}

void a(void){
  b(2);
}

int main(){
  a();
  return 0;
}

gcc 3.1 disassembly: 
8000198c <b>:
8000198c:	24850002 	addiu	a1,a0,2
80001990:	3c048403 	lui	a0,0x8403
80001994:	27bdffe8 	addiu	sp,sp,-24
80001998:	afbf0010 	sw	ra,16(sp)
8000199c:	0c002b57 	jal	8000ad5c <printf>
800019a0:	24848000 	addiu	a0,a0,-32768
800019a4:	8fbf0010 	lw	ra,16(sp)
800019a8:	00000000 	nop
800019ac:	03e00008 	jr	ra
800019b0:	27bd0018 	addiu	sp,sp,24

800019b4 <a>:
800019b4:	27bdffe8 	addiu	sp,sp,-24
800019b8:	afbf0010 	sw	ra,16(sp)
800019bc:	0c000663 	jal	8000198c <b>
800019c0:	24040002 	li	a0,2
800019c4:	8fbf0010 	lw	ra,16(sp)
800019c8:	00000000 	nop
800019cc:	03e00008 	jr	ra
800019d0:	27bd0018 	addiu	sp,sp,24

800019d4 <main>:
800019d4:	27bdffe8 	addiu	sp,sp,-24
800019d8:	afbf0010 	sw	ra,16(sp)
800019dc:	0c00066d 	jal	800019b4 <a>
800019e0:	00000000 	nop
800019e4:	8fbf0010 	lw	ra,16(sp)
800019e8:	00001021 	move	v0,zero
800019ec:	03e00008 	jr	ra
800019f0:	27bd0018 	addiu	sp,sp,24

gcc 4.0 disassembly:
80001980 <b>:
80001980:	24850002 	addiu	a1,a0,2
80001984:	3c048402 	lui	a0,0x8402
80001988:	08002b4a 	j	8000ad28 <printf>
8000198c:	24840100 	addiu	a0,a0,256

80001990 <a>:
80001990:	08000660 	j	80001980 <b>
80001994:	24040002 	li	a0,2

80001998 <main>:
80001998:	27bdffe8 	addiu	sp,sp,-24
8000199c:	afbf0010 	sw	ra,16(sp)
800019a0:	0c000664 	jal	80001990 <a>
800019a4:	00000000 	nop
800019a8:	8fbf0010 	lw	ra,16(sp)
800019ac:	00001021 	move	v0,zero
800019b0:	03e00008 	jr	ra
800019b4:	27bd0018 	addiu	sp,sp,24

--
run with 4.0 version:

(gdb) info breakpoints
Num Type           Disp Enb Address    What
1   breakpoint     keep y   0xffffffff80001998 in main at tmp.c:11
2   breakpoint     keep y   0xffffffff800019b0 in main at tmp.c:14

(gdb) p/x $pc
$1 = 0x80001998

(gdb) step
(gdb) p/x $pc
$2 = 0x800019a0

(gdb) set debug remote 1
(gdb) step
Sending packet: $m80001998,4#70...Ack
Packet received: 27bdffe8
Sending packet: $M80001998,4:0005000d#43...Ack
Packet received: OK
Sending packet: $m800019b0,4#91...Ack
Packet received: 03e00008
Sending packet: $M800019b0,4:0005000d#64...Ack
Packet received: OK
Sending packet: $s#73...Ack
Packet received: S05
Sending packet: $p25#d7...Ack
Packet received: 800019a4
Sending packet: $s#73...Ack
Packet received: S05
Sending packet: $p25#d7...Ack
Packet received: 80001990
Sending packet: $p1d#05...Ack
Packet received: 8402ba60
Sending packet: $p1f#07...Ack
Packet received: 800019a8
Sending packet: $m8000199c,4#9b...Ack
Packet received: afbf0010
Sending packet: $m800019a0,4#90...Ack
Packet received: 0c000664
Sending packet: $m800019a4,4#94...Ack
Packet received: 00000000
Sending packet: $c#63...Ack
Packet received: S02
Sending packet: $p25#d7...Ack
Packet received: 800019b0

--
Backtrace taken right before the above continue:

#0  remote_resume (ptid={pid = -1, lwp = 0, tid = 0}, step=0,
    siggnal=TARGET_SIGNAL_0) at ../../GDB-ISS/gdb/remote.c:2603
#1  0x004240bb in resume (step=0, sig=TARGET_SIGNAL_0)
    at ../../GDB-ISS/gdb/infrun.c:624
#2  0x004278b7 in keep_going (ecs=0x22d810) at
../../GDB-ISS/gdb/infrun.c:2825
#3  0x00427606 in step_into_function (ecs=0x22d810)
    at ../../GDB-ISS/gdb/infrun.c:2708
#4  0x00426d3a in handle_inferior_event (ecs=0x22d810)
    at ../../GDB-ISS/gdb/infrun.c:2433
#5  0x0042467f in wait_for_inferior () at
../../GDB-ISS/gdb/infrun.c:1000
#6  0x004244c7 in proceed (addr=18446744073709551615,
    siggnal=TARGET_SIGNAL_DEFAULT, step=1) at
../../GDB-ISS/gdb/infrun.c:825
#7  0x00417cc4 in step_1 (skip_subroutines=0, single_inst=0,
count_string=0x0)
    at ../../GDB-ISS/gdb/infcmd.c:717
#8  0x004179ff in step_command (count_string=0x0, from_tty=1)
    at ../../GDB-ISS/gdb/infcmd.c:606