Re: [PATCH 2/2] Add test for fast tracepoint enable/disable

Simon Marchi
2016-04-01T14:42:16Z

On 16-04-01 09:36 AM, Yao Qi wrote:
> Simon Marchi <simon.marchi@ericsson.com> writes:
>
>> Good question. Because the setup for testing fast tracepoints is
>> tedious, I always
>> use ftrace-lock.exp as a template, because it is relatively short.
>> ftrace-lock.exp
>> uses gdb_compile_pthreads. I think it makes sense, because the IPA
>> starts a helper
>> thread with pthread_create.
>
> gdb_compile_pthreads is used in ftrace-lock.exp because ftrace-lock.c is
> a multi-threaded program, but ftrace-enable-disable.c isn't. The
> program to be tested is running in one thread, and it doesn't have any
> interaction with the helper thread.
>
>>
>> Note that it still builds fine with gdb_compile instead of gdb_compile_pthreads,
>> probably because libinproctrace.so has a DT_NEEDED for libpthreads.so,
>> so it gets
>> pulled in. But using gdb_compile_pthreads should add -pthread to the
>> CFLAGS, which
>> may impact compilation (e.g. choose re-entrant versions of functions).
>
> Using IPA/fast tracepoint shouldn't affect how the program is compiled.
> User is writing and debugging a single thread program, and he/she wants
> to use fast tracepoint to debug. He/She shouldn't recompile the program
> with -lpthreads or -pthreads, what needed here is to let IPA be loaded with
> the program.

That totally makes sense, I'll change it to gdb_compile.

>>
>> However, I just noticed that the command line includes -lpthreads
>> instead of -pthreads:
>>
>> spawn gcc -Wl,--no-as-needed
>> /home/emaisin/build/binutils-gdb/gdb/testsuite/../../../../src/binutils-gdb/gdb/testsuite/gdb.trace/ftrace-enable-disable.c
>> \
>> /home/emaisin/build/binutils-gdb/gdb/testsuite/../gdbserver/libinproctrace.so
>> -g \
>> -lpthread -lm -o \
>> /home/emaisin/build/binutils-gdb/gdb/testsuite/outputs/gdb.trace/ftrace-enable-disable/ftrace-enable-disable
>>
>> I think that to be more "correct", we should try -pthread before -lpthread in
>> gdb_compile_pthreads...
>
> I am not sure, it is a separate issue, this applies to all test cases
> compiled with gdb_compile_pthreads.
>