Can I call dr_app_setup_and_start in a signal handler ?

[吕志宏]

I want to perform tracing at a certain stage during application execution. Is it possible to call `dr_app_setup_and_start` by sending a signal? Or is there a better alternative?

[Kai Luk]

Could you modify the application?

> If the application can be modified, it can be linked with the \p drmemtrace
tracer and use DynamoRIO's start/stop API routines dr_app_setup_and_start()
and dr_app_stop_and_cleanup() to delimit the desired trace region.

Please see https://github.com/DynamoRIO/dynamorio/blob/master/suite/tests/api/static_sideline.c

for an example.

Kai 

[Derek Bruening]

If you cannot modify the application, you can use instruction counts to delay tracing (-trace_after_instrs), or trim the trace in post-processing (-trim_before_instr).

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[吕志宏]

Hi, I'm using `drrun attach` to try and take over a test program, but I'm encountering a problem. After execution, there's no response. Using gdb, I see that the `drrun` program is stuck in a `dr_inject_wait_for_child` loop, seemingly unable to wait for the child thread to exit. My test program is a user-space program similar to DPDK, and the child threads are all polling. I'd like to ask if there are any solutions?

[吕志宏]

I suspect the program might be blocking or ignoring certain Dynamorio essential signals. Are there any signals that the program cannot block or ignore?

[Derek Bruening]

For the start/stop interface, yes: but it's usually SIGILL: see https://github.com/DynamoRIO/dynamorio/blob/master/core/unix/os.c#L995.

For ptrace attach, no, I don't think it should matter as it uses ptrace to attach and once in control it does a decent job of distinguishing its own from app signals.

But ptrace attach in the middle of certain syscalls can be tricky: see PR #5462 and the earlier code #5019 talking about auto-restart syscall issues.

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