Messages in this thread | | | Date | Tue, 10 May 2016 11:45:11 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: kgdb: Match pstate size with gdbserver protocol |
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On Mon, May 09, 2016 at 06:39:26PM +0100, Daniel Thompson wrote: > 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 44679a4f142b ("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.
While that was how we discovered the inconsistency, a major concern is that SPSR_EL* (i.e. PSTATE), as accessed by MRS/MSR is a 64-bit quantity, even if the upper 32 bits are RES0 today.
It is conceivable that the upper 32 bits could be used in future (as happened with CLIDR_EL1), and for this reason we expose those upper 32 bits from the kernel, and treat system registers as 64-bit quantities generally.
So this was also about ensuring the interface was consistent and to some extent future-proof.
Thanks, Mark.
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