[ILUG] GDB Macros of the day

[paul at clubi.ie]

On Thu, 4 Mar 2010, Josh Glover wrote:

> Damn, Paul! I just suggested gdb because Frank mentioned it; were 
> it myself in need of a backtrace, I'd simply send SIGSEGV to the 
> offending process group and rip into the resulting core files with 
> a binary editor (hex is for sissies). That I wrote myself. In IA64 
> machine code. With unrolled loops. Using an Atari paddle controller 
> as a binary input device. Running at 400 baud on a serial port 
> driver that I wrote myself. Loaded at runtime into a kernel that I 
> wrote myself. In IA64 machine code...

Hehe, very good.

I myself prefer the method of "laying on hands", where one debugs 
SEGVs by connecting physically with the machine, being at one with 
the silicon and sensing the aura of its electro-magnetic emanations.

I find crystals help purify those auras and enhances the debugging 
process. Indeed, I can supply some, at a very good price (tastefully 
packaged together with an IC, stamped "Dallas Semiconductor" of 
course).

Also quite useful are macros. E.g. when debugging on big-endian 
machines (cause I'm not leet like those who do this in their heads):

define def_ntohs
  set $data = (char *)$arg0
  set $i = 0

  set $_  = $data[$i++] << 8
  set $_ += $data[$i++]
end
document def_ntohs
Read a 2-byte short at the given pointed to area as big-endian and
return it in $_

Argument: Pointer to a 2-byte, big-endian short word.
Returns: Integer value of that word in $_
end

define def_ntohl
  set $data = (char *)$arg0
  set $i = 0

  set $_  = $data[$i++] << 24
  set $_ += $data[$i++] << 16
  set $_ += $data[$i++] << 8
  set $_ += $data[$i++]
end
document def_ntohl
Read a 4-byte integer at the given pointed to area as big-endian and
return it in $_

Argument: Pointer to a big-endian 4-byte word.
Returns: Integer value of that word in $_
end

regards,
-- 
Paul Jakma	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
The absurd is the essential concept and the first truth.
 		-- A. Camus