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Wed, 13 May 2020 16:06:55 -0700 (PDT) From: Douglas Anderson To: Jason Wessel , Daniel Thompson Subject: [PATCH] arm64: Call debug_traps_init() from trap_init() to help early kgdb Date: Wed, 13 May 2020 16:06:37 -0700 Message-Id: <20200513160501.1.I0b5edf030cc6ebef6ab4829f8867cdaea42485d8@changeid> X-Mailer: git-send-email 2.26.2.645.ge9eca65c58-goog MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200513_160658_003602_FDBF0FAF X-CRM114-Status: GOOD ( 20.24 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.4 on bombadil.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:442 listed in] [list.dnswl.org] 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.0 SPF_PASS SPF: sender matches SPF record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.0 DKIMWL_WL_HIGH DKIMwl.org - Whitelisted High sender X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , sumit.garg@linaro.org, "Paul E. McKenney" , Will Deacon , Greg Kroah-Hartman , Enrico Weigelt , kgdb-bugreport@lists.sourceforge.net, jinho lim , Douglas Anderson , linux-kernel@vger.kernel.org, Alexios Zavras , James Morse , "Eric W. Biederman" , Catalin Marinas , Zenghui Yu , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , liwei391@huawei.com, Dave Martin , Allison Randal , Masami Hiramatsu Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org A new kgdb feature will soon land (kgdb_earlycon) that lets us run kgdb much earlier. In order for everything to work properly it's important that the break hook is setup by the time we process "kgdbwait". Right now the break hook is setup in debug_traps_init() and that's called from arch_initcall(). That's a bit too late since kgdb_earlycon really needs things to be setup by the time the system calls dbg_late_init(). We could fix this by adding call_break_hook() into early_brk64() and that works fine. However, it's a little ugly. Instead, let's just add a call to debug_traps_init() straight from trap_init(). There's already a documented dependency between trap_init() and debug_traps_init() and this makes the dependency more obvious rather than just relying on a comment. NOTE: this solution isn't early enough to let us select the "ARCH_HAS_EARLY_DEBUG" KConfig option that is introduced by the kgdb_earlycon patch series. That would only be set if we could do breakpoints when early params are parsed. This patch only enables "late early" breakpoints, AKA breakpoints when dbg_late_init() is called. It's expected that this should be fine for most people. It should also be noted that if you crash you can still end up in kgdb earlier than debug_traps_init(). Since you don't need breakpoints to debug a crash that's fine. Suggested-by: Will Deacon Signed-off-by: Douglas Anderson Cc: Catalin Marinas Cc: Will Deacon Acked-by: Will Deacon --- This replaces the patch ("arm64: Add call_break_hook() to early_brk64() for early kgdb") in my recent kgdb series [1]. If I end up re-posting that series again I'll include this patch as a replacement, but I'm sending it separately to avoid spamming a pile of people another time with a 12-patch series. Note that, because it doesn't select the "ARCH_HAS_EARLY_DEBUG" KConfig option it could be landed standalone. However, it's still probably better to land together with that patch series. If the kgdb_earlycon patch series lands without this patch then kgdbwait + kgdb_earlycon won't work well on arm64, but there would be no other bad side effects. If this patch lands without the kgdb_earlycon patch series then there will be no known problems. [1] https://lore.kernel.org/r/20200507130644.v4.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid arch/arm64/include/asm/debug-monitors.h | 2 ++ arch/arm64/kernel/debug-monitors.c | 4 +--- arch/arm64/kernel/traps.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h index 7619f473155f..e5ceea213e39 100644 --- a/arch/arm64/include/asm/debug-monitors.h +++ b/arch/arm64/include/asm/debug-monitors.h @@ -125,5 +125,7 @@ static inline int reinstall_suspended_bps(struct pt_regs *regs) int aarch32_break_handler(struct pt_regs *regs); +void debug_traps_init(void); + #endif /* __ASSEMBLY */ #endif /* __ASM_DEBUG_MONITORS_H */ diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index 48222a4760c2..15e80c876d46 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -376,15 +376,13 @@ int aarch32_break_handler(struct pt_regs *regs) } NOKPROBE_SYMBOL(aarch32_break_handler); -static int __init debug_traps_init(void) +void __init debug_traps_init(void) { hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, TRAP_TRACE, "single-step handler"); hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP, TRAP_BRKPT, "ptrace BRK handler"); - return 0; } -arch_initcall(debug_traps_init); /* Re-enable single step for syscall restarting. */ void user_rewind_single_step(struct task_struct *task) diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index cf402be5c573..8408e8670f2e 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -1047,11 +1047,11 @@ int __init early_brk64(unsigned long addr, unsigned int esr, return bug_handler(regs, esr) != DBG_HOOK_HANDLED; } -/* This registration must happen early, before debug_traps_init(). */ void __init trap_init(void) { register_kernel_break_hook(&bug_break_hook); #ifdef CONFIG_KASAN_SW_TAGS register_kernel_break_hook(&kasan_break_hook); #endif + debug_traps_init(); }