Attach lldb debugger to the compiled program's executable when the main executable is not the compiled program

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fueledbypizza OP

Created Oct ’24

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I am building an MPI C project in Xcode. In order to do run it, I had to:

Specify /path/to/mpiexec in Edit Scheme -> Run -> Info -> Executable, instead of the "default" one, say myprogram if my target is called myprogram.
Specify the following arguments in Edit Scheme -> Run -> Arguments -> Arguments Passed On Launch: -np 4, ${BUILT_PRODUCTS_DIR}/${EXECUTABLE_NAME}

This is clearly analogous to a mpiexec -np 4 a.out command launched on terminal.

The problem is, when I want to debug my application, the execution doesn't "stop" on the breakpoints.
I instantly thought that it is because of the check box Debug Executable in Edit Scheme -> Run -> Info -> Executable. Indeed (as I have just said), the Executable specified in there is mpiexec and not myprogram.

Thus, is there an option or some command I could set in Xcode to attach the lldb to myprogram?

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Answer 1

DTS Engineer OP

Apple

Oct ’24

It’s hard to answer this without knowing how mpiexec does what it’s doing. Do you have insight into that?

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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Answer 2

DTS Engineer OP

Apple

Oct ’24

It’s better if you reply as a reply; if you reply in the comments, I might not see it. See Quinn’s Top Ten DevForums Tips for this and other titbits.

Can you go a little deeper with your question?

I’m presuming that mpiexec runs your executabel as a child process. What API does it use for that? fork/exec{ve}? posix_spawn? Something else? And does it do anything special to ‘detach’ the child from itself?

Also, am I right in assuming that -np 4 means that it’ll run 4 child processes? If so, are you expecting to get 4 instances of the debugger, each one attached to a different child?

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

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