[PATCH v2 00/10] arm64: Use BRK instruction for generic BUG traps

Dave Martin
2015-07-13T13:25:47Z

Changes since v1:

* Modified BRK immediate for BUG so that it doesn't overlap the range
allocated for KGDB.

* Typo fixes.

* Don't assume that BUG() kills the thread, so that catching BUGs in
kgdb works again.

* Separate header for the BRK immediates removed, at Will's request.
I've retained the other refactoring since it contains useful tidy-
ups, but some of that could go away if desired.

Original cover letter:

Currently, the minimal default BUG() implementation from asm-generic is
used for arm64.

This series 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 eliminates a fair amount of
inlined code at BUG() and WARN() sites.

This work makes it look increasingly desirable to collect BRK immediates
together in one place. Patches 1-7 do some refactoring to prepare for
this, and patch 8 moves the definitions to a fresh header, <asm/brk.h>.

Patch 9 provides the BRK-based GENERIC_BUG support for arm64.

A side-effect of this change is that WARNs are now generated via a
different bit of generic code (lib/bug.c:report_bug()) that no longer
prints a backtrace (compare kernel/panic.c:warn_slowpath_common()).) I
will post a separate mini-RFC series to address that in the generic
code. Patch 10 hacks a backtrace back into the arm64 arch code in the
meantime.

Comments and testing welcome.

Quick testing suggests a kernel size reduction of ~110K for arm64
defconfig.

Dave Martin (10):
arm64/debug: Eliminate magic number for size of BRK instruction
arm64/debug: Mask off all reserved bits from generated ESR values
arm64: esr.h type fixes and cleanup
arm64/debug: Eliminate magic number from ESR template definition
arm64/debug: More consistent naming for the BRK ESR template macro
arm64/debug: Move BRK ESR template macro into <asm/esr.h>
arm64/debug: Simplify BRK insn opcode declarations
arm64/debug: Add missing #include
arm64/BUG: Use BRK instruction for generic BUG traps
arm64/BUG: Show explicit backtrace for WARNs

arch/arm64/Kconfig | 8 ++
arch/arm64/include/asm/bug.h | 64 +++++++++++++++
arch/arm64/include/asm/debug-monitors.h | 36 +++------
arch/arm64/include/asm/esr.h | 135 ++++++++++++++++---------------
arch/arm64/include/asm/memory.h | 3 +-
arch/arm64/kernel/kgdb.c | 12 +--
arch/arm64/kernel/traps.c | 61 +++++++++++++-
arch/arm64/mm/fault.c | 12 ++-
8 files changed, 233 insertions(+), 98 deletions(-)
create mode 100644 arch/arm64/include/asm/bug.h

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1.7.10.4