sysroot and coredump debugging

sysroot and coredump debugging

[Lluís Batlle i Rossell via Gdb]

Hello,

I have an target system, for which I have a sysroot path in my
development computer. Both GNU/Linux.

I expect that I can run this in my development computer, after downloading
the core dump from the target system:
(gdb) set sysroot /mysysroot
(gdb) file myelf  #  it has debug info
(gdb) core-file core

And this never works; it drops the file with the symbols, thinking it's
unrelated to the core dump:

warning: Can't open file /home/user/myelf during file-backed mapping note
processing
warning: core file may not match specified executable file.

Nothing works with dynamic libs loaded either. The only way I can make gdb
to allow me to debug the core dump with symbols is by copying the elf to
"/mysysroot/home/user/myelf", as it was in the target system.

Is this expected? It is very annoying. Why should the elf of the
executable sit within the sysroot in an exact place, to debug a core dump?

I use gdb 15.2 but this happens at least since gdb 11. Maybe it is fixed
in a newer version?

Thank you,
Lluís.

Re: sysroot and coredump debugging

[Luis Machado via Gdb]

On 4/23/25 14:06, Lluís Batlle i Rossell via Gdb wrote:
> Hello,
> 
> I have an target system, for which I have a sysroot path in my
> development computer. Both GNU/Linux.
> 
> I expect that I can run this in my development computer, after downloading
> the core dump from the target system:
> (gdb) set sysroot /mysysroot
> (gdb) file myelf  #  it has debug info
> (gdb) core-file core
> 
> And this never works; it drops the file with the symbols, thinking it's
> unrelated to the core dump:
> 
> warning: Can't open file /home/user/myelf during file-backed mapping note
> processing
> warning: core file may not match specified executable file.
> 
> Nothing works with dynamic libs loaded either. The only way I can make gdb
> to allow me to debug the core dump with symbols is by copying the elf to
> "/mysysroot/home/user/myelf", as it was in the target system.
> 
> Is this expected? It is very annoying. Why should the elf of the
> executable sit within the sysroot in an exact place, to debug a core dump?
> 
> I use gdb 15.2 but this happens at least since gdb 11. Maybe it is fixed
> in a newer version?
> 
> Thank you,
> Lluís.

Unfortunately I think this is an area where improvements could be made. I know
we have "substitute-path", but that's only for sources. In theory setting sysroot
should work, but it doesn't seem to.

We want gdb to be strict about making sure the core file matches the ELF file, but
we could have some adjustability here.

Re: sysroot and coredump debugging

[Lluís Batlle i Rossell via Gdb]

On Thu, Apr 24, 2025 at 03:01:56PM +0100, Luis Machado wrote:
> On 4/23/25 14:06, Lluís Batlle i Rossell via Gdb wrote:
> > I expect that I can run this in my development computer, after downloading
> > the core dump from the target system:
> > (gdb) set sysroot /mysysroot
> > (gdb) file myelf  #  it has debug info
> > (gdb) core-file core
> > 
> > And this never works; it drops the file with the symbols, thinking it's
> > unrelated to the core dump:
> > 
> > warning: Can't open file /home/user/myelf during file-backed mapping note
> > processing
> > warning: core file may not match specified executable file.
> 
> Unfortunately I think this is an area where improvements could be made. I know
> we have "substitute-path", but that's only for sources. In theory setting sysroot
> should work, but it doesn't seem to.
> 
> We want gdb to be strict about making sure the core file matches the ELF file, but
> we could have some adjustability here.

The "same absolute path" is never required when debugging core dumps
without sysroot, for dump/elf matching. Why does the sysroot introduce
that requirement? It looks like there is a small mistake somewhere, rather
than intended behavior.