Years ago, in the time of IRIX-6.2, I wrote a very tiny (just one
screen of code) debugger for single-stepping, inspired in the code I
found in an old book (whose name I don't remember). Such code was
based on ptrace(). It used to work fine, but I tried it today with a
current IRIX version, and it no longer works (once the child is in
trace mode, all subsequent ptrace calls return "No such process" --I
tried it with a lot of executables and the error was always the same
--that error never happened with 6.2).

After googling, I found that ptrace() is not recommended in IRIX, and
that the "/proc" way of life should be used instead. Maybe that's the
reason of the errors I'm getting.

Can anybody point me to sample code of the simplest single-stepping
debugger which could be written with /proc?  I already looked at the
source code of some debuggers, but they're too big to be used as a
sample for learning.

Can the simplest /proc-based debugger be as _tiny_ as the simplest
ptrace-based one?

TIA

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In article <55b15169.0406260622.4b5864a@posting.google.com>,
jabro <jabroeng@yahoo.com> wrote:
>Years ago, in the time of IRIX-6.2, I wrote a very tiny (just one
>screen of code) debugger for single-stepping, inspired in the code I
>found in an old book (whose name I don't remember). Such code was
>based on ptrace(). It used to work fine, but I tried it today with a
>current IRIX version, and it no longer works (once the child is in
>trace mode, all subsequent ptrace calls return "No such process" --I
>tried it with a lot of executables and the error was always the same
>--that error never happened with 6.2).
>
>After googling, I found that ptrace() is not recommended in IRIX, and
>that the "/proc" way of life should be used instead. Maybe that's the
>reason of the errors I'm getting.

We have not tested ptrace in years.
So your result is not particularly surprising.

>Can anybody point me to sample code of the simplest single-stepping
>debugger which could be written with /proc?  I already looked at the
>source code of some debuggers, but they're too big to be used as a
>sample for learning.
>
>Can the simplest /proc-based debugger be as _tiny_ as the simplest
>ptrace-based one?

I believe so, but am not going to try to prove it :-)

Use open(2) on the /proc/<pid>.
Use the resulting fd to do ioctl()s on the process.
Use PIOCSTOP to stop the process, PIOCRUN (with flag PRSTEP) to step
the process.

The documented /proc operations work on the process.
Not per-thread, but on all threads (if it is a pthreads process, I mean).

david anderson

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