[RESEND PATCH] arm64: kgdb: fix single stepping
takahiro.akashi at linaro.org
Thu Sep 15 00:56:18 PDT 2016
On Wed, Sep 14, 2016 at 03:58:51PM +0100, Will Deacon wrote:
> Hi Akashi,
> On Tue, Apr 21, 2015 at 02:13:13AM +0100, AKASHI Takahiro wrote:
> > Could you please review my patch below?
> > See also arm64 maintainer's comment:
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/313712.html
> -ETIMEDOUT waiting for the kdgb folk to comment. Ppeople have reported
> that this patch is required for kgdb to work correctly on arm64, so I'm
> happy to merge it.
I'm happy, too.
> However, as detailed in your comment log:
> > This patch
> > (1) moves kgdb_disable_single_step() from 'c' command handling to single
> > step handler.
> > This makes sure that single stepping gets effective at every 's' command.
> > Please note that, under the current implementation, single step bit in
> > spsr, which is cleared by the first single stepping, will not be set
> > again for the consecutive 's' commands because single step bit in mdscr
> > is still kept on (that is, kernel_active_single_step() in
> > kgdb_arch_handle_exception() is true).
> > (2) re-implements kgdb_roundup_cpus() because the current implementation
> > enabled interrupts naively. See below.
> > (3) removes 'enable_dbg' in el1_dbg.
> > Single step bit in mdscr is turned on in do_handle_exception()->
> > kgdb_handle_expection() before returning to debugged context, and if
> > debug exception is enabled in el1_dbg, we will see unexpected single-
> > stepping in el1_dbg.
> > Since v3.18, the following patch does the same:
> > commit 1059c6bf8534 ("arm64: debug: don't re-enable debug exceptions
> > on return from el1_dbg)
> > (4) masks interrupts while single-stepping one instruction.
> > If an interrupt is caught during processing a single-stepping, debug
> > exception is unintentionally enabled by el1_irq's 'enable_dbg' before
> > returning to debugged context.
> > Thus, like in (2), we will see unexpected single-stepping in el1_irq.
> this patch is doing *far* too much in one go. Could you please repost it
> as a series of self-contained fixes with clear commit messages, so I can
> queue them and cc stable where appropriate?
Sure, but I need to refresh my memory here.
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