malloc in inferior

["John S. Yates, Jr." <jyates at netezza dot com>]

I have finally figured out that the reason gdb
keeps crashing my embedded system is that it
tries to call malloc at the drop of a hat.

There are various contexts in our code where
performing a memory allocation is disallowed.
This is enforced by our allocation primitives.

Our system does not uses malloc.  The malloc
that is part of the c-runtime calls through a
null function pointer, triggering a machine
reset.  So something as simple as

(gdb) print "foo"

causes a crash.

Why can gdb not allocate values within its own
address space?

I understand that to support calling functions
in the inferior gdb may have to materialize
values there.  But these should be pushed into
the inferior once it is clear that they need to
exist there.

And how can gdb possibly debug a multi-threaded
application with a thread-safe malloc?

One possibility would be to add malloc and free
messages to the remote protocol.  Then a stub
could allocation memory in the proper address
space without interacting with the inferior's
environment.

Another would be to have a stub provide a block
of memory.  A query would determine the address
and size of this block.  Then gdb could manage
the memory entirely on its own.

/john
--
John S. Yates, Jr.   508 665-6897 (voice)
Netezza Inc          508 665-6811 (fax)
200 Crossing Blvd.   Framingham, MA 01701