Hi Roland, On Wed, 2023-05-31 at 16:44 -0700, Roland McGrath via Elfutils-devel wrote: > In elfutils, the libdwfl library is responsible for the "library for > obtaining debug info writ large" stuff. It provides <argp.h> API parsers > for command-line arguments that mesh with its library stuff like > Dwfl_Callbacks that set the search path used equivalently to GDB's `set > debug-file-directory` path. eu-* tools as well as things like systemtap use > this to accept `--debuginfo-path=PATH`, but AFAIK none of them support > environment variables. In the binutils world outside of GDB itself, I > think only objdump and readelf do .build-id/... lookup and those use common > binutils-private code (binutils/dwarf.c) that just has a hard-coded > directory list. Some more uniformity here would be beneficial to everyone, > I think.
One difference is that the elfutils and gdb traditional "search path" mechanism is mainly based on path/file names (lookups through .gnu_debuglink, possibly relative .debug dirs/files) while the primary lookup method for libdebuginfod is based on build-id. libdebuginfod kind of assumes you already know the traditional lookup didn't work. That is also how dwfl_standard_find_debuginfo uses libdebuginfod. It first gets the build-id from the ELF file, looks for that in the traditional way (/usr/lib/debug/.build-id/xx/yyyy.debug), if that fails it does a path based search (using the file name, debuglink file name and Dwfl_Callbacks debuginfo_path), and if that also fails then it tries to use libdebuginfod. Another difference is the lookup of .dwz files. Since they contain an "artificial" build-id, libdebuginfod uses that to look them up as if a "normal" .debug file. While the traditional lookup uses the (relative!) path in the .gnu_debugaltlink section of the .debug file. I wonder which parts of the "traditional" lookup are still useful/relevant. Could we get away with pointing at a "traditional" /usr/lib/debug/ like path that contains a .build-id and (optional) .dwz subdir to make libdebuginfo that "uniform" debug file lookup library? Cheers, Mark
