Re: [PATCH] Support gzip compressed exec and core files in gdb

Michael Eager
2015-03-12T15:34:07Z

On 03/12/15 03:41, Pedro Alves wrote:

> Waiting for GDB to decompress that once is already painful. Waiting for it
> multiple times likely results in cursing and swearing at gdb's slow start
> up. Smart users will realize that and end up decompressing the file manually
> outside gdb, just once, anyway, thus saving time.
>
> We could "fix" the "multiple times" issue by adding even more smarts,
> based on an already-decompressed-files cache or some such. Though of
> course, more smarts, more code to maintain.

I had considered adding a command or command line option to specify
the name of the uncompress file, so that it could be reused.

> I agree with Jan -- The real convenience would be being able to skip the
> long whole-file decompression step altogether, with an on-demand
> block-decompress scheme, because gdb in reality doesn't need to touch
> most of the vast majority of the core dump's contents. That would
> be a solution that I'd be happy to see implemented.

That's a solution to a different problem.

> If we're just decompressing to /tmp, then we also need to
> compare the benefits of a built-in solution against having users
> do the same with a user-provided gdb command implemented in one
> of gdb's extensions languages (python, scheme), e.g., a command
> that adds a "decompress-core" command that does the same:
> decompresses whatever compression format, and loads the result
> with "core /tmp/FILE".

This requires that users manually decompress files, and makes it
impossible to put the compressed file name on the command line.

It also looks to me like a wart and kludge, rather than having
GDB automatically identify the compression method and do the
operation transparently for the user.

> IMO, whatever the solution, if built in, this is best implemented
> in BFD, so that objdump can dump the same files gdb can.

I took that approach initially. But GDB finds and opens files,
not BFD. Moving what GDB is doing into BFD, where it should have
been in the first place (IMO), seemed more problematic.

--
Michael Eager eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306 650-325-8077