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Date: Fri, 19 Oct 2012 08:30:53 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: Problem Compiling gdbserver with musl

On Fri, Oct 19, 2012 at 02:13:12PM +0800, Brian Wang wrote:
> Hello all,
> 
> Is it possible to cross compile gdbserver with musl?  I tried it and
> it failed complaining about some thread-db stuff:

I'm not sure how to get gdb to build on musl. I have not done it
myself, but I've heard that some of musl's users/packagers have done
it. Hopefully someone else can jump in with a good answer.

> --------------
> thread-db.c: In function ‘find_one_thread’:
> thread-db.c:292:7: error: format ‘%ld’ expects argument of type ‘long
> int’, but argument 3 has type ‘thread_t’ [-Werror=format]

These are because gdb assumes pthread_t is an integer type. musl uses
an opaque pointer type, both for convenience and robustness against
common programming errors (the compiler can report mixups/misordering
of arguments much better).

> thread-db.c:652:3: error: passing argument 1 of ‘dladdr’ discards
> ‘const’ qualifier from pointer target type [-Werror]

Not sure what caused this one.

> In file included from thread-db.c:33:0:
> /opt/cross/arm-linux-musleabi/lib/gcc/arm-linux-musleabi/4.7.1/../../../../arm-linux-musleabi/include/dlfcn.h:30:5:
> note: expected ‘void *’ but argument is of type ‘const void *’
> thread-db.c: In function ‘try_thread_db_load_from_sdir’:
> thread-db.c:708:30: error: ‘LIBTHREAD_DB_SO’ undeclared (first use in
> this function)
> [...]
> --------------
> 
> Is there a separate libthread_db library for musl?

No, and I have not yet figured out what it would entail to get gdb
supporting threads better with musl. Implementing the full
libpthread_db interface glibc provides would be very invasive in terms
of size and possibly performance. But hopefully it's possible to get
it working quite well without so much. Are you aware of any
documentation on what gdb really needs?

FYI, thread debugging support code is not necessary to get gdb
working; it's only necessary for the debugger to support interaction
with threads at runtime.

Rich

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