Re: Location of vmlinux debuginfo file

[Roland McGrath <roland at redhat dot com>]

> I was wrong in my original email. SLES puts vmlinux-`uname -r`.debug in 
> /usr/lib/debug/boot.  If I create a link from that file to 
> /usr/lib/debug/boot/vmlinux-`uname -r` it works.

Ah.  But there is no file called /boot/vmlinux-`uname -r`.

> I'm not seeing where it ever tries to open a corresponding 
> /usr/lib/debug/boot/vmlinux-`uname -r`.debug file. 

It doesn't.  If /boot/vmlinux-`uname -r` existed and was an ELF file
containing a .gnu.debuglink section giving the name vmlinux-`uname -r`.debug,
then it would look for a /usr/lib/debug/boot/vmlinux-`uname -r`.debug file.

The standard debuginfo-finding behavior is based on starting with a
stripped ELF file that the debuginfo corresponds to.  Given that there
isn't any such file for the kernel in many setups, it is certainly
reasonable to look for /usr/lib/debug/boot/vmlinux-`uname -r`.debug as a
special case (at least as reasonable as looking for
/usr/lib/debug/boot/vmlinux-`uname -r`).  

> I also see various attempts to open files in a .debug subdirectory.  
> Is that a standard place for debuginfo files?

The default debuginfo_path is ":.debug:/usr/lib/debug".
The libdwfl.h comments on dwfl_standard_find_debuginfo describe what the
path setting means:

/* Standard find_debuginfo callback function.
   This is controlled by a string specifying directories to look in.
   If `debuginfo_path' is set in the Dwfl_Callbacks structure
   and the char * it points to is not null, that supplies the string.
   Otherwise a default path is used.

   If the first character of the string is + or - that says to check or to
   ignore (respectively) the CRC32 checksum from the .gnu_debuglink
   section.  The default is to check it.  The remainder of the string is
   composed of elements separated by colons.  Each element can start with +
   or - to override the global checksum behavior.  If the remainder of the
   element is empty, the directory containing the main file is tried; if
   it's an absolute path name, the absolute directory path containing the
   main file is taken as a subdirectory of this path; a relative path name
   is taken as a subdirectory of the directory containing the main file.
   Hence for /bin/ls, string ":.debug:/usr/lib/debug" says to look in /bin,
   then /bin/.debug, then /usr/lib/debug/bin, for the file name in the
   .gnu_debuglink section (or "ls.debug" if none was found).  */