[llvm-dev] Slow debugger starts of LLVM tools

David Jones via llvm-dev llvm-dev at lists.llvm.org
Wed Jan 9 13:44:48 PST 2019

GDB likes to load all symbols from shared libraries up front. And on x86_64
your main executable is really just another shared library.

So yes, it's slow. The sloth is proportional to the size of the object(s)
being debugged. It's not just LLVM, it's any large (i.e. 100+MB to 1+GB)
executable+library footprint.

On Wed, Jan 9, 2019 at 4:28 PM David Greene via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'm wondering if anyone else is running into this problem.
> When I do a Debug build and attempt to run a tool (opt, llvm-dis,
> whatever) in gdb, the program takes a LOOOOONG time to begin executing.
> Loading the executable into gdb is not the problem.  I type "run" and
> the debugger sits there for many seconds and then things start going.
> gdb emits no messages indicating what it is doing but it's basically
> using 100% CPU.
> I'm wondering if this is an artifact of the gdb I'm using (buggy?) or
> something inherent to the way LLVM tools are built.  I see the same slow
> operation across different versions of gdb and I do not see the same
> slow operation with other executables.
>                          -David
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