• Daniel Thompson's avatar
    arm64: kgdb: Match pstate size with gdbserver protocol · 0d15ef67
    Daniel Thompson authored
    Current versions of gdb do not interoperate cleanly with kgdb on arm64
    systems because gdb and kgdb do not use the same register description.
    This patch modifies kgdb to work with recent releases of gdb (>= 7.8.1).
    
    Compatibility with gdb (after the patch is applied) is as follows:
    
      gdb-7.6 and earlier  Ok
      gdb-7.7 series       Works if user provides custom target description
      gdb-7.8(.0)          Works if user provides custom target description
      gdb-7.8.1 and later  Ok
    
    When commit 44679a4f ("arm64: KGDB: Add step debugging support") was
    introduced it was paired with a gdb patch that made an incompatible
    change to the gdbserver protocol. This patch was eventually merged into
    the gdb sources:
    https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=a4d9ba85ec5597a6a556afe26b712e878374b9dd
    
    The change to the protocol was mostly made to simplify big-endian support
    inside the kernel gdb stub. Unfortunately the gdb project released
    gdb-7.7.x and gdb-7.8.0 before the protocol incompatibility was identified
    and reversed:
    https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=bdc144174bcb11e808b4e73089b850cf9620a7ee
    
    This leaves us in a position where kgdb still uses the no-longer-used
    protocol; gdb-7.8.1, which restored the original behaviour, was
    released on 2014-10-29.
    
    I don't believe it is possible to detect/correct the protocol
    incompatiblity which means the kernel must take a view about which
    version of the gdb remote protocol is "correct". This patch takes the
    view that the original/current version of the protocol is correct
    and that version found in gdb-7.7.x and gdb-7.8.0 is anomalous.
    Signed-off-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    0d15ef67
kgdb.h 3.79 KB