From: mark.rutland@arm.com (Mark Rutland)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 09/10] arm64/BUG: Use BRK instruction for generic BUG traps
Date: Mon, 13 Jul 2015 17:43:15 +0100 [thread overview]
Message-ID: <20150713164315.GC22840@leverpostej> (raw)
In-Reply-To: <1436793967-7138-10-git-send-email-Dave.Martin@arm.com>
Hi,
On Mon, Jul 13, 2015 at 02:25:56PM +0100, Dave P Martin wrote:
> Currently, the minimal default BUG() implementation from asm-
> generic is used for arm64.
>
> This patch uses the BRK software breakpoint instruction to generate
> a trap instead, similarly to most other arches, with the generic
> BUG code generating the dmesg boilerplate.
>
> This allows bug metadata to be moved to a separate table and
> reduces the amount of inline code at BUG and WARN sites. This also
> avoids clobbering any registers before they can be dumped.
>
> To mitigate the size of the bug table further, this patch makes
> use of the existing infrastructure for encoding addresses within
> the bug table as 32-bit offsets instead of absolute pointers.
> (Note that this limits the kernel size to 2GB.)
>
> Traps are registered at arch_initcall time for aarch64, but BUG
> has minimal real dependencies and it is desirable to be able to
> generate bug splats as early as possible. This patch redirects
> all debug exceptions caused by BRK directly to bug_handler() until
> the full debug exception support has been initialised.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
FWIW I've given this a spin and it seems to work, so:
Tested-by: Mark Rutland <mark.rutland@arm.com>
I have one concern with this below.
> +#ifndef _ARCH_ARM64_ASM_BUG_H
> +#define _ARCH_ARM64_ASM_BUG_H
> +
> +#include <asm/debug-monitors.h>
> +
> +#ifdef CONFIG_GENERIC_BUG
> +#define HAVE_ARCH_BUG
> +
> +#ifdef CONFIG_DEBUG_BUGVERBOSE
> +#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
> +#define __BUGVERBOSE_LOCATION(file, line) \
> + ".pushsection .rodata.str,\"aMS\", at progbits,1\n" \
> + "2: .string \"" file "\"\n\t" \
> + ".popsection\n\t" \
> + \
> + ".long 2b - 0b\n\t" \
> + ".short " #line "\n\t"
> +#else
> +#define _BUGVERBOSE_LOCATION(file, line)
> +#endif
Given the reliance on the labels in the caller, I think it might make
more sense to fold this into __BUG_FLAGS, and just have an #ifdef in the
middle.
That would also mean passing file and line to the macro for the general
case, like on arch/arm (even if !CONFIG_DEBUG_BUGVERBOSE), and moving
the double-indirection of those out to the caller.
Otherwise this looks good to me.
As an aside, it looks to me like the arch/arm implementation never
allocates space for flags in each bug_entry, which I would have expected
to mess up the bug table. I must be missing something there.
Thanks,
Mark.
> +
> +#define _BUG_FLAGS(flags) __BUG_FLAGS(flags)
> +
> +#define __BUG_FLAGS(flags) asm volatile ( \
> + ".pushsection __bug_table,\"a\"\n\t" \
> + ".align 2\n\t" \
> + "0: .long 1f - 0b\n\t" \
> +_BUGVERBOSE_LOCATION(__FILE__, __LINE__) \
> + ".short " #flags "\n\t" \
> + ".popsection\n" \
> + \
> + "1: brk %[imm]" \
> + :: [imm] "i" (BUG_BRK_IMM) \
> +)
> +
> +#define BUG() do { \
> + _BUG_FLAGS(0); \
> + unreachable(); \
> +} while (0)
> +
> +#define __WARN_TAINT(taint) _BUG_FLAGS(BUGFLAG_TAINT(taint))
> +
> +#endif /* ! CONFIG_GENERIC_BUG */
> +
> +#include <asm-generic/bug.h>
> +
> +#endif /* ! _ARCH_ARM64_ASM_BUG_H */
next prev parent reply other threads:[~2015-07-13 16:43 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-13 13:25 [PATCH v2 00/10] arm64: Use BRK instruction for generic BUG traps Dave Martin
2015-07-13 13:25 ` [PATCH v2 01/10] arm64/debug: Eliminate magic number for size of BRK instruction Dave Martin
2015-07-13 14:47 ` Mark Rutland
2015-07-13 13:25 ` [PATCH v2 02/10] arm64/debug: Mask off all reserved bits from generated ESR values Dave Martin
2015-07-13 14:14 ` Mark Rutland
2015-07-13 14:22 ` Dave Martin
2015-07-13 13:25 ` [PATCH v2 03/10] arm64: esr.h type fixes and cleanup Dave Martin
2015-07-14 15:54 ` Mark Rutland
2015-07-14 16:53 ` Dave Martin
2015-07-13 13:25 ` [PATCH v2 04/10] arm64/debug: Eliminate magic number from ESR template definition Dave Martin
2015-07-13 14:16 ` Mark Rutland
2015-07-13 13:25 ` [PATCH v2 05/10] arm64/debug: More consistent naming for the BRK ESR template macro Dave Martin
2015-07-13 14:19 ` Mark Rutland
2015-07-13 13:25 ` [PATCH v2 06/10] arm64/debug: Move BRK ESR template macro into <asm/esr.h> Dave Martin
2015-07-13 14:18 ` Mark Rutland
2015-07-13 13:25 ` [PATCH v2 07/10] arm64/debug: Simplify BRK insn opcode declarations Dave Martin
2015-07-13 14:38 ` Mark Rutland
2015-07-13 13:25 ` [PATCH v2 08/10] arm64/debug: Add missing #include Dave Martin
2015-07-13 14:34 ` Mark Rutland
2015-07-13 14:44 ` Dave Martin
2015-07-13 14:45 ` Mark Rutland
2015-07-13 13:25 ` [PATCH v2 09/10] arm64/BUG: Use BRK instruction for generic BUG traps Dave Martin
2015-07-13 16:43 ` Mark Rutland [this message]
2015-07-13 16:51 ` Dave Martin
2015-07-13 16:56 ` Mark Rutland
2015-07-13 17:05 ` Dave P Martin
2015-07-14 10:20 ` Dave Martin
2015-07-14 11:09 ` Mark Rutland
2015-07-14 11:34 ` Dave Martin
2015-07-14 15:51 ` Mark Rutland
2015-07-14 16:53 ` Dave Martin
2015-07-14 16:11 ` Catalin Marinas
2015-07-14 16:55 ` Dave Martin
2015-07-13 13:25 ` [PATCH v2 10/10] arm64/BUG: Show explicit backtrace for WARNs Dave Martin
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