Re: [PATCH RFA] procfs.c related changes for AIX 5

[Kevin Buettner <kevinb@cygnus.com>]

On Mar 6, 11:07am, Eli Zaretskii wrote:

> On Mon, 5 Mar 2001, Kevin Buettner wrote:
> 
> >  2) AIX5 does not have a static set of syscalls.  Consequently, there
> >     is no sys/syscall.h file which provides a nice mapping of
> >     symbolic names to syscall numbers.  Instead, AIX5 provides
> >     /proc/PID/sysent which contains the information necessary to map
> >     strings to syscall numbers.
> >     
> >     These syscall numbers are guaranteed (at least according to the
> >     developer that I spoke with) to be fixed for the lifetime of a
> >     process, but they can certainly vary between processes.
> 
> Won't this cause problems with debugging syscall-related code, since
> the values for GDB and the debuggee may be different?

GDB knows the pid of the debuggee and interogates its syscall
numbers in /proc/PID/sysent.  I.e, it gets the syscall numbers
for the child process that it's debugging from the /proc filesystem.

If you're asking about actually debugging code that contains syscalls,
I'm not sure I see how this enters the picture.  Does GDB have some
additional knowledge of syscall numbers somewhere that I'm not aware
of?

BTW, for a given release of the OS, I think there is a subset of the
syscall numbers that'll be fixed and won't change.  So, in theory,
it'd be possible to use a table of #defines for these, but to the best
of my knowledge, IBM hasn't provided any in their header files.

> >     The changes needed to the code due to this change were fairly
> >     significant:
> > 
> >     a) sysset_t data structures (or data structures which contain
> >        sysset_t) must be dynamically allocated.  They must be
> >        copied with memcpy() and explicitly freed when no longer
> >        needed.
> > 
> >     b) Comparisons against SYS_* constants no longer work.  I've
> >        introduced a number of predicate functions (such as
> >        syscall_is_exit()) which will indicate whether a
> >        given system call number is a particular system call.  All code
> >        which formerly relied on comparisons against a system call
> >        number was rewritten to call one of these new predicate
> >        functions instead.
> 
> Shouldn't these be documented somehow in gdbint.texinfo?

Probably.  (I'll take a look.)