The branch main has been updated by mhorne: URL: https://cgit.FreeBSD.org/src/commit/?id=874635e381731e1fbd5e2d0459ca87814f1e455c
commit 874635e381731e1fbd5e2d0459ca87814f1e455c Author: Mitchell Horne <[email protected]> AuthorDate: 2021-03-01 13:59:25 +0000 Commit: Mitchell Horne <[email protected]> CommitDate: 2021-03-01 14:04:22 +0000 arm64: fix hardware single-stepping from EL1 The main issue is that debug exceptions must to be disabled for the entire duration that SS bit in MDSCR_EL1 is set. Otherwise, a single-step exception will be generated immediately. This can occur before returning from the debugger (when MDSCR is written to) or before re-entering it after the single-step (when debug exceptions are unmasked in the exception handler). Solve this by delaying the unmask to C code for EL1, and avoid unmasking at all while handling debug exceptions, thus avoiding any recursive debug traps. Reviewed by: markj, jhb MFC after: 5 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D28944 --- sys/arm64/arm64/debug_monitor.c | 6 ++++++ sys/arm64/arm64/exception.S | 6 +++++- sys/arm64/arm64/trap.c | 8 ++++++++ 3 files changed, 19 insertions(+), 1 deletion(-) diff --git a/sys/arm64/arm64/debug_monitor.c b/sys/arm64/arm64/debug_monitor.c index eb5d19567697..c6622650f1ad 100644 --- a/sys/arm64/arm64/debug_monitor.c +++ b/sys/arm64/arm64/debug_monitor.c @@ -186,6 +186,9 @@ void kdb_cpu_set_singlestep(void) { + KASSERT((READ_SPECIALREG(daif) & PSR_D) == PSR_D, + ("%s: debug exceptions are not masked", __func__)); + kdb_frame->tf_spsr |= DBG_SPSR_SS; WRITE_SPECIALREG(mdscr_el1, READ_SPECIALREG(mdscr_el1) | DBG_MDSCR_SS | DBG_MDSCR_KDE); @@ -205,6 +208,9 @@ void kdb_cpu_clear_singlestep(void) { + KASSERT((READ_SPECIALREG(daif) & PSR_D) == PSR_D, + ("%s: debug exceptions are not masked", __func__)); + WRITE_SPECIALREG(mdscr_el1, READ_SPECIALREG(mdscr_el1) & ~(DBG_MDSCR_SS | DBG_MDSCR_KDE)); diff --git a/sys/arm64/arm64/exception.S b/sys/arm64/arm64/exception.S index 9fe825fd12b5..9a28a5eac022 100644 --- a/sys/arm64/arm64/exception.S +++ b/sys/arm64/arm64/exception.S @@ -75,8 +75,12 @@ __FBSDID("$FreeBSD$"); ldr x0, [x18, #(PC_CURTHREAD)] bl dbg_monitor_enter -.endif msr daifclr, #8 /* Enable the debug exception */ +.endif + /* + * For EL1, debug exceptions are conditionally unmasked in + * do_el1h_sync(). + */ .endm .macro restore_registers el diff --git a/sys/arm64/arm64/trap.c b/sys/arm64/arm64/trap.c index cb3a05ad0163..d793e34a6894 100644 --- a/sys/arm64/arm64/trap.c +++ b/sys/arm64/arm64/trap.c @@ -377,6 +377,14 @@ do_el1h_sync(struct thread *td, struct trapframe *frame) "do_el1_sync: curthread: %p, esr %lx, elr: %lx, frame: %p", td, esr, frame->tf_elr, frame); + /* + * Enable debug exceptions if we aren't already handling one. They will + * be masked again in the exception handler's epilogue. + */ + if (exception != EXCP_BRK && exception != EXCP_WATCHPT_EL1 && + exception != EXCP_SOFTSTP_EL1) + dbg_enable(); + switch (exception) { case EXCP_FP_SIMD: case EXCP_TRAP_FP: _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/dev-commits-src-all To unsubscribe, send any mail to "[email protected]"
