• Ingo Molnar's avatar
    x86/debug: Remove perpetually broken, unmaintainable dwarf annotations · 131484c8
    Ingo Molnar authored
    So the dwarf2 annotations in low level assembly code have
    become an increasing hindrance: unreadable, messy macros
    mixed into some of the most security sensitive code paths
    of the Linux kernel.
    
    These debug info annotations don't even buy the upstream
    kernel anything: dwarf driven stack unwinding has caused
    problems in the past so it's out of tree, and the upstream
    kernel only uses the much more robust framepointers based
    stack unwinding method.
    
    In addition to that there's a steady, slow bitrot going
    on with these annotations, requiring frequent fixups.
    There's no tooling and no functionality upstream that
    keeps it correct.
    
    So burn down the sick forest, allowing new, healthier growth:
    
       27 files changed, 350 insertions(+), 1101 deletions(-)
    
    Someone who has the willingness and time to do this
    properly can attempt to reintroduce dwarf debuginfo in x86
    assembly code plus dwarf unwinding from first principles,
    with the following conditions:
    
     - it should be maximally readable, and maximally low-key to
       'ordinary' code reading and maintenance.
    
     - find a build time method to insert dwarf annotations
       automatically in the most common cases, for pop/push
       instructions that manipulate the stack pointer. This could
       be done for example via a preprocessing step that just
       looks for common patterns - plus special annotations for
       the few cases where we want to depart from the default.
       We have hundreds of CFI annotations, so automating most of
       that makes sense.
    
     - it should come with build tooling checks that ensure that
       CFI annotations are sensible. We've seen such efforts from
       the framepointer side, and there's no reason it couldn't be
       done on the dwarf side.
    
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Frédéric Weisbecker <fweisbec@gmail.com
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Jan Beulich <JBeulich@suse.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    131484c8
memcpy_64.S 3.24 KB