Re: [Elftoolchain-developers] elf_update() returns error "Invalid data buffer descriptor" on FreeBSD 10.3

[Ed M. <em...@fr...>]

On 15 May 2016 at 22:05, Sam Habiel <sam...@gm...> wrote:
>
> Having said that though, I don't have enough experience in FreeBSD to
> be able to answer all your questions; and I never had to use gdb to
> debug a linked library before. Let me answer and ask in turns:

Sorry about that - I wasn't sure how much or little detail to provide.
I'm happy to work through the details with you.

> 1. I downloaded FreeBSD 10.3 and libelf came with the system without
> me installing anything. I presume then it's in the FreeBSD source tree
> since I didn't install that one from the ports tree, correct?

That's correct.

jkoshy@ and others developed the BSD-licensed libelf in FreeBSD
starting in the mid-2000s, and it's still that version that's in
FreeBSD 10.

libelf and other tools moved from FreeBSD to the ELF Tool Chain
project  out to ELF Tool Chain later on, and were reimported into
FreeBSD for FreeBSD 11.

> 2. Where is the upstream version? And how can I compile it to replace
> the ones that my makefile grabs? (I think I can figure this one out,
> but a hint will help).

You can get it here:
svn checkout svn://svn.code.sf.net/p/elftoolchain/code/trunk elftoolchain-code
A top level 'make' will build libelf, libdwarf, and ELF Tool Chain
versions of strip, nm, size, etc.

Adding -L (and -I) options to CFLAGS when building your software
should be sufficient to pick it up. You mentioned that it works with a
libelf from ports, and the same scheme used to build against that one
should work for your own elftoolchain build.

> 3. How do use gdb to step into such a library? Would just typing "s"
> take you into the code if everything else is in place?

Yes. You can build the library with -g, and -O0 to make debugging work
better. E.g., with flags for 2. and 3.:
CFLAGS="-g -O0 -L/example/src/elftoolchain/libelf
-I/example/src/elftoolchain/libelf" make

You can set a breakpoint on elf_update, and then step through to find
out where the error is returned.