From 8effeaaf2cacc8a8007d3089e253e7baaff57bb7 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Wed, 21 Jun 2017 18:11:23 +0100 Subject: [PATCH] arm64: dump cpu_hwcaps at panic time When debugging a kernel panic(), it can be useful to know which CPU features have been detected by the kernel, as some code paths can depend on these (and may have been patched at runtime). This patch adds a notifier to dump the detected CPU caps (as a hex string) at panic(), when we log other information useful for debugging. On a Juno R1 system running v4.12-rc5, this looks like: [ 615.431249] Kernel panic - not syncing: Fatal exception in interrupt [ 615.437609] SMP: stopping secondary CPUs [ 615.441872] Kernel Offset: disabled [ 615.445372] CPU features: 0x02086 [ 615.448522] Memory Limit: none A developer can decode this by looking at the corresponding bits. For example, the above decodes as: * bit 1: ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE * bit 2: ARM64_WORKAROUND_845719 * bit 7: ARM64_WORKAROUND_834220 * bit 13: ARM64_HAS_32BIT_EL0 Signed-off-by: Mark Rutland Acked-by: Steve Capper Cc: Catalin Marinas Cc: Suzuki K Poulose Cc: Will Deacon Signed-off-by: Will Deacon --- arch/arm64/kernel/cpufeature.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 55d5c72a507d..9f9e0064c8c1 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -51,6 +51,25 @@ unsigned int compat_elf_hwcap2 __read_mostly; DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS); EXPORT_SYMBOL(cpu_hwcaps); +static int dump_cpu_hwcaps(struct notifier_block *self, unsigned long v, void *p) +{ + /* file-wide pr_fmt adds "CPU features: " prefix */ + pr_emerg("0x%*pb\n", ARM64_NCAPS, &cpu_hwcaps); + return 0; +} + +static struct notifier_block cpu_hwcaps_notifier = { + .notifier_call = dump_cpu_hwcaps +}; + +static int __init register_cpu_hwcaps_dumper(void) +{ + atomic_notifier_chain_register(&panic_notifier_list, + &cpu_hwcaps_notifier); + return 0; +} +__initcall(register_cpu_hwcaps_dumper); + DEFINE_STATIC_KEY_ARRAY_FALSE(cpu_hwcap_keys, ARM64_NCAPS); EXPORT_SYMBOL(cpu_hwcap_keys); -- 2.20.1