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Re: GDB: Does "catch vfork" work?


Daniel Jalkut wrote :

SystemUIServer uses vfork to spawn a new process for the screencapture invocation. In the process of examining gdb's facilities for working with multiple processes, I noticed the intriguing "catch" command.

I thought I would test it out on SystemUIServer since I know it calls vfork. But "catch vfork" doesn't seem to work. Setting a breakpoint on vfork works. I notice that "catch start" kindly informs me that it's not implemented yet. Should "catch vfork" be saying the same thing?

And out of curiosity, what are the benefits of using "catch" as opposed to "break" when the thing that's being caught corresponds to a system call? "catch start" sounds cool because it doesn't correspond to a system call. I guess that may be why it's not implemented yet :)

"catch" is very different from "break" : "break" allow you to add a breackpoint on a known function or at an arbitrary memory address, "catch" allow you to add a breakpoint at a given event in a generic way and which may be difficult to set with standard breakpoints (for "catch throw" for instance).

There may also be a problem with the process followed by gdb. When you use vfork, the system create a new process, but gdb may only debug on process at the same. It must choose to follow the parent process or the child process. The default behaviour is to follow the parent process, but you may change it with the gdb "set follow-fork- mode child" command.

--
Damien Bobillot

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 >GDB: Does "catch vfork" work? (From: Daniel Jalkut <email@hidden>)



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