gdb follows symlinks when looking for debuginfo

gdb follows symlinks when looking for debuginfo

[Olaf Hering]

Why does gdb follow symlinks when looking for debuginfo and executables?

The binaries in our installation images are symlinked into a
loop-mounted cramfs image, or to an extracted tree on a remote
filesystem.
The gdb binary itself is a symlink /usr/bin/gdb ->
/mounts/inst-sys/usr/bin/gdb. For some reason, gdb starts to look for
debuginfo in /mounts/inst-sys/usr/lib/debug instead of just
/usr/lib/debug. The same is true for the executable thats being
debugged.

How can this be turned off? I do not see a cmdline switch for that.

Re: gdb follows symlinks when looking for debuginfo

[Daniel Jacobowitz]

On Wed, Jan 23, 2008 at 05:15:37PM +0100, Olaf Hering wrote:
> 
> Why does gdb follow symlinks when looking for debuginfo and executables?

Most likely something uses realpath when opening files.  Looks like
exec_file_attach -> openp -> xfullpath.

> The binaries in our installation images are symlinked into a
> loop-mounted cramfs image, or to an extracted tree on a remote
> filesystem.
> The gdb binary itself is a symlink /usr/bin/gdb ->
> /mounts/inst-sys/usr/bin/gdb. For some reason, gdb starts to look for
> debuginfo in /mounts/inst-sys/usr/lib/debug instead of just
> /usr/lib/debug. The same is true for the executable thats being
> debugged.

That path is surprising.  I would have expected
/usr/lib/debug/mounts/inst-sys/...  Does "show sysroot"
show anything?  What about "show debug-file-directory"?

-- 
Daniel Jacobowitz
CodeSourcery

Re: gdb follows symlinks when looking for debuginfo

[Olaf Hering]

On Wed, Jan 23, Daniel Jacobowitz wrote:

> On Wed, Jan 23, 2008 at 05:15:37PM +0100, Olaf Hering wrote:
> > 
> > Why does gdb follow symlinks when looking for debuginfo and executables?
> 
> Most likely something uses realpath when opening files.  Looks like
> exec_file_attach -> openp -> xfullpath.
> 
> > The binaries in our installation images are symlinked into a
> > loop-mounted cramfs image, or to an extracted tree on a remote
> > filesystem.
> > The gdb binary itself is a symlink /usr/bin/gdb ->
> > /mounts/inst-sys/usr/bin/gdb. For some reason, gdb starts to look for
> > debuginfo in /mounts/inst-sys/usr/lib/debug instead of just
> > /usr/lib/debug. The same is true for the executable thats being
> > debugged.
> 
> That path is surprising.  I would have expected
> /usr/lib/debug/mounts/inst-sys/...  Does "show sysroot"
> show anything?  What about "show debug-file-directory"?

The current system root is "".
The directory where separate debug symbols are searched for is "/mounts/instsys/usr/lib/debug".

You are right. I should have pasted the correct path into the mail.

For 3 yast libs (the first 3 libs to load), the path is wrong.

inst-sys:/ # grep y2wfm.so /X
2953  open("/usr/lib/YaST2/plugin/libpy2wfm.so.2", O_RDONLY) = 7
2953  stat64("/usr/lib/YaST2/plugin/libpy2wfm.so.2", {st_mode=S_IFREG|0755, st_size=121048, ...}) = 0
2953  open("/usr/lib/YaST2/plugin/libpy2wfm.so.2", O_RDONLY) = 7
2953  open("/mounts/instsys/usr/lib/YaST2/plugin/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
2953  open("/mounts/instsys/usr/lib/YaST2/plugin/.debug/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
2953  open("/mounts/instsys/usr/lib/debug//mounts/instsys/usr/lib/YaST2/plugin/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
2953  open("/mounts/instsys/usr/lib/debug/mounts/instsys/usr/lib/YaST2/plugin/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)

Should have been /mounts/instsys/usr/lib/debug/usr/lib/YaST2/plugin/libpy2wfm.so.2.0.0.debug
Maybe wrong debuginfo generated by gcc? They are not dlopen objects.

For all others the debuginfo can be loaded.
inst-sys:/ # grep libexpat.so.1 /X
2953  open("/lib/libexpat.so.1", O_RDONLY) = 3
2953  open("/lib/libexpat.so.1", O_RDONLY) = 13
2953  stat64("/lib/libexpat.so.1", {st_mode=S_IFREG|0755, st_size=193996, ...}) = 0
2953  open("/lib/libexpat.so.1", O_RDONLY) = 5
2953  open("/lib/libexpat.so.1.5.2.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
2953  open("/lib/.debug/libexpat.so.1.5.2.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
2953  open("/mounts/instsys/usr/lib/debug//lib/libexpat.so.1.5.2.debug", O_RDONLY) = 6
2953  stat64("/mounts/instsys/usr/lib/debug//lib/libexpat.so.1.5.2.debug", {st_mode=S_IFREG|0644, st_size=289219, ...}) = 0
2953  open("/mounts/instsys/usr/lib/debug//lib/libexpat.so.1.5.2.debug", O_RDONLY) = 6

The gdb output is:
...............
Reading symbols from /mounts/instsys/usr/lib/YaST2/plugin/libpy2wfm.so.2...expanding to full symbols...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/YaST2/plugin/libpy2wfm.so.2
Reading symbols from /mounts/instsys/usr/lib/YaST2/plugin/libpy2scr.so.2...expanding to full symbols...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/YaST2/plugin/libpy2scr.so.2
Reading symbols from /mounts/instsys/usr/lib/YaST2/plugin/libpy2UI.so.2...expanding to full symbols...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/YaST2/plugin/libpy2UI.so.2
Reading symbols from /usr/lib/libscr.so.2...expanding to full symbols...Reading symbols from /mounts/instsys/usr/lib/debug/usr/lib/libscr.so.2.0.0.debug...expanding to full symbols...done.
done.
..............

Why are the first 3 libs searched in  /mounts/instsys instead of /?

Re: gdb follows symlinks when looking for debuginfo

[Daniel Jacobowitz]

On Wed, Jan 23, 2008 at 07:04:28PM +0100, Olaf Hering wrote:
> For 3 yast libs (the first 3 libs to load), the path is wrong.

Are these the only ones symlinked?  I bet this:

> 2953  open("/usr/lib/YaST2/plugin/libpy2wfm.so.2", O_RDONLY) = 7

is a symlink to /mounts/instsys, and this:

> 2953  open("/lib/libexpat.so.1", O_RDONLY) = 3

is not.

I don't know what to suggest.  The real location of the file, on an
installed system, is probably relative to where the real debug info
will be found.

You can work around this with a couple of creative symlinks.  For
instance:

> 2953  open("/mounts/instsys/usr/lib/YaST2/plugin/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
> 2953  open("/mounts/instsys/usr/lib/YaST2/plugin/.debug/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
> 2953  open("/mounts/instsys/usr/lib/debug//mounts/instsys/usr/lib/YaST2/plugin/libpy2wfm.so.2.0.0.debug", O_RDONLY) = -1 ENOENT (No such file or directory)

The third path is wrong for you, but you can make the second path
right.  Symlink /mounts/instsys/usr/lib/YaST2/plugin/.debug to
/mounts/instsys/usr/lib/debug/usr/lib/YaST2/plugin.

-- 
Daniel Jacobowitz
CodeSourcery

Re: gdb follows symlinks when looking for debuginfo

[Olaf Hering]

On Wed, Jan 23, Daniel Jacobowitz wrote:

> On Wed, Jan 23, 2008 at 07:04:28PM +0100, Olaf Hering wrote:
> > For 3 yast libs (the first 3 libs to load), the path is wrong.
> 
> Are these the only ones symlinked?  I bet this:
> 
> > 2953  open("/usr/lib/YaST2/plugin/libpy2wfm.so.2", O_RDONLY) = 7
> 
> is a symlink to /mounts/instsys, and this:

The YaST2 directory is a symlink:
/usr/lib/YaST2 -> /mounts/instsys/usr/lib/YaST2

> > 2953  open("/lib/libexpat.so.1", O_RDONLY) = 3
> 
> is not.

/lib/libexpat.so.1 -> libexpat.so.1.5.2 -> /mounts/instsys/lib/libexpat.so.1.5.2

I will create a tmpfs bind mount to store the debuginfo in
/mounts/instsys/usr/lib/debug. This will work for all libs, except the
ones in /usr/lib/YaST2/plugin/