[OE-core] Debugging using sysroots and GDB

[Richard Purdie]

On Fri, 2016-03-04 at 15:06 +0100, Pascal Bach wrote:
> > It really depends on your view of what the sysroot is used for. We
> > intentionally strip a variety of things out of it as things work
> > today
> > basically for size/performance reasons. If we start putting
> > debugging
> > source in there, it will become huge and this will image the size
> > of
> > things like eSDK and affect the speed of operations like building
> > from
> > sstate.
> 
> From my point of view debugging from sysroots is not mandatory if I
> can find a suitable alternative.
> One thing I want to avoid is to install -dbg packages to my image.
> 
> What I currently do is the following:
> 
> 1. Enable Debugfs generation using: `IMAGE_GEN_DEBUGFS = "1"`
> 2. Switch debug split style to: `PACKAGE_DEBUG_SPLIT_STYLE = "debug
> -file-directory"`
> 
> After building the image I end up with a rootfs and a rootfs-dbg
> 
> 3. Extract both rootfs and rootfs-dbg somewhere (/home/projects)
> 4. Setup gdb with the following .gdbinit:
> 
> ```
> set sysroot /home/projects/rootfs
> set debug-file-directory /home/projects/rootfs-dbg/usr/lib/debug
> set substitute-path /usr/src/debug /home/projects/rootfs
> -dbg/usr/src/debug
> ```
> 
> With this setup I'm able to debug trough all libraries on the system.
> So so far so good.
> 
> However for this to work I need to change the
> `PACKAGE_DEBUG_SPLIT_STYLE` to a non default and this made me wonder
> if I missed something.
> - Is there a way to get this setup working with the default ".debug"
> style of OE?
> - If not why is the .debug style the default instead of "debug-file
> -directory"?
> - Is there any documentation? I was unable to find anything more than
> [1] in the Yocto Mega manual.
> - Is there some best practice I missed?

Using this method is a supported approach. I'm a little surprised
.debug directories don't work. Have you tried just setting:

set sysroot /home/projects/rootfs-dbg
set substitute-path /usr/src/debug /home/projects/rootfs
-bbg/usr/src/debug

as I believe it should work with IMAGE_GEN_DEBUGFS=1 "out the box". If
it doesn't that is a bug and we should try and look into fixing that.

Cheers,

Richard