RE: single stepping mips remote programs built with gcc 4.0

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

 

> You've talked about GDB inserting breakpoints for software
> single-stepping, but you're not using software single-stepping here. 
> Those memory writes are for your user breakpoints at the entry point
> and exit point of main.  The 's' packet indicates that the stub itself
> is doing the single-stepping.

Which run?  The first run I had a user breakpoint at the very beginning of main, the second run I had the breakpoint one instruction after the beginning.

Run 1:

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) 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 <-- user breakpoint
Packet received: OK
Sending packet: $m800019b0,4#91...Ack
Packet received: 03e00008
Sending packet: $M800019b0,4:0005000d#64...Ack <-- user breakpoint
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  

----
Run 2:

Num Type           Disp Enb Address    What
2   breakpoint     keep y   0xffffffff800019b0 in main at tmp.c:14
3   breakpoint     keep y   0xffffffff8000199c in main at tmp.c:11 <-- one instruction later than run 1

Sending packet: $m800019b0,4#91...Ack
Packet received: 03e00008
Sending packet: $M800019b0,4:0005000d#64...Ack <-- user breakpoint
Packet received: OK
Sending packet: $m8000199c,4#9b...Ack
Packet received: afbf0010
Sending packet: $M8000199c,4:0005000d#6e...Ack <-- user breakpoint
Packet received: OK
Sending packet: $Hc0#db...Ack
Packet received: ENN
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: $m80001998,4#70...Ack
Packet received: 27bdffe8
Sending packet: $m800019a0,4#90...Ack
Packet received: 0c000664
Sending packet: $m800019a4,4#94...Ack
Packet received: 00000000
Sending packet: $m80001998,4#70...Ack
Packet received: 27bdffe8
Sending packet: $M80001998,4:0005000d#43...Ack <-- not user breakpoint
Packet received: OK
Sending packet: $c#63...Ack
Packet received: S02
Sending packet: $p25#d7...Ack
Packet received: 800019b0

> 
> > 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
> 
> This is weird.  It looks like GDB is doing some prologue analysis
> here, but it's not starting at any function's entry point.  That,
> combined with the fact that you said that disassembly shows you the
> wrong code, makes me wonder if the debug info is right.
> 
> When you say 'print &a' or 'print &main', do you get the 
> right addresses?
  
Yes, I get the right addresses. When I disassemble the functions in the console I get the right thing too.
But when I use insight to show an assembly listing of a particular function, it shows the function after.  I did not realize that disassembling in the console and showing the assembly of a function with insight could give different results. 

I said something inaccurate before -- I was compiling this program with "-gstabs+" , not "-g".  I have seen different behavior depending on if I use "-g" or "-gstabs+" with some other programs, but I just tried both flags and it doesn't seem to make a difference here.