Re: Using LD_PRELOAD in testsuite to extend gdb test coverage

[Yao Qi <yao at codesourcery dot com>]

On 03/04/2014 11:40 AM, Doug Evans wrote:
> My current motivation for this is an example that arose today where
> gdb doesn't properly handle attaching to a program where a thread dies
> before gdb can attach to it.  With this library, preloaded into gdb, I
> can intercept ptrace calls (and others as needed) and, e.g., delay
> them until the library detects the inferior is in the desired state
> (arranged by however the library and the testcase wish to do so).

This kind of tests can be complementary to existing dejagnu-based test
cases, because dejagnu test cases are hard to drive GDB to a specific
state which is needed for testing.

> 
> For implementation, I envision a .c file that contains all the
> administrivia needed by an LD_PRELOAD library, plus some hooks that
> let a .c provided by the testcase easily use it.  Then link the two
> into the LD_PRELOAD library.

That sounds reasonable.  FWIW, I used LD_PRELOAD mechanism to intercept
ptrace calls too to emulate that GDB is communicating with a remote
GDBserver or a slow jtag probe, in order to find performance issues when
GDB is talking with slow stubs.
> 
> Obviously, such tests would only work on appropriate systems, but I
> think providing a means to easily write such tests on such systems is
> important enough.
> If it's not a lot of code (my prototype is pretty straightforward),
> and it provides a means to more easily test such cases, why not do it?

I can't figure out how much tests cases can/should be written in this
way.  If only one or two test cases are written in this way, we can
start from a simple LD_PRELOAD library, and generalize it as needed
in the future.

-- 
Yao (éå)