Date: Thu, 21 Mar 2024 10:13:47 GMT From: Andrew Turner <andrew@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: ed3c6cd76de8 - main - arm64: Mask non-debug exceptions when single stepping Message-ID: <202403211013.42LADloU032400@gitrepo.freebsd.org>
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The branch main has been updated by andrew: URL: https://cgit.FreeBSD.org/src/commit/?id=ed3c6cd76de8560c46607abe506a03568e9acab2 commit ed3c6cd76de8560c46607abe506a03568e9acab2 Author: Andrew Turner <andrew@FreeBSD.org> AuthorDate: 2024-03-14 14:02:56 +0000 Commit: Andrew Turner <andrew@FreeBSD.org> CommitDate: 2024-03-21 10:13:24 +0000 arm64: Mask non-debug exceptions when single stepping When an exception is pending when single stepping we may execute the handler for that exception rather than the single step handler. This could cause the scheduler to fire to run a new thread. This will mean we single step to a new thread causing unexpected results. Handle this by masking non-debug exceptions. This will cause issues when stepping over instructions that access the DAIF values so future work is needed to handle these cases, but for most code this now works as expected. Reviewed by: jhb Sponsored by: Arm Ltd Differential Revision: https://reviews.freebsd.org/D44350 --- sys/arm64/arm64/debug_monitor.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/sys/arm64/arm64/debug_monitor.c b/sys/arm64/arm64/debug_monitor.c index b8164b70c5c8..480a6da817a2 100644 --- a/sys/arm64/arm64/debug_monitor.c +++ b/sys/arm64/arm64/debug_monitor.c @@ -193,6 +193,15 @@ kdb_cpu_set_singlestep(void) ("%s: debug exceptions are not masked", __func__)); kdb_frame->tf_spsr |= PSR_SS; + + /* + * TODO: Handle single stepping over instructions that access + * the DAIF values. On a read the value will be incorrect. + */ + kernel_monitor.dbg_flags &= ~PSR_DAIF; + kernel_monitor.dbg_flags |= kdb_frame->tf_spsr & PSR_DAIF; + kdb_frame->tf_spsr |= (PSR_A | PSR_I | PSR_F); + WRITE_SPECIALREG(mdscr_el1, READ_SPECIALREG(mdscr_el1) | MDSCR_SS | MDSCR_KDE); @@ -214,6 +223,9 @@ kdb_cpu_clear_singlestep(void) KASSERT((READ_SPECIALREG(daif) & PSR_D) == PSR_D, ("%s: debug exceptions are not masked", __func__)); + kdb_frame->tf_spsr &= ~PSR_DAIF; + kdb_frame->tf_spsr |= kernel_monitor.dbg_flags & PSR_DAIF; + WRITE_SPECIALREG(mdscr_el1, READ_SPECIALREG(mdscr_el1) & ~(MDSCR_SS | MDSCR_KDE));
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