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As there are several discussions for enabling perf breakpoint signal
testing on arm64 platform: arm64 needs to rely on single-step to execute
the breakpointed instruction and then reinstall the breakpoint exception
handler. But if we hook the breakpoint with a signal, the signal
handler will do the stepping rather than the breakpointed instruction,
this causes infinite loops as below:
Kernel space | Userspace
---------------------------------|--------------------------------
| __test_function() -> hit
| breakpoint
breakpoint_handler() |
`-> user_enable_single_step() |
do_signal() |
| sig_handler() -> Step one
| instruction and
| trap to kernel
single_step_handler() |
`-> reinstall_suspended_bps() |
| __test_function() -> hit
| breakpoint again and
| repeat up flow infinitely
As Will Deacon mentioned [1]: "that we require the overflow handler to
do the stepping on arm/arm64, which is relied upon by GDB/ptrace. The
hw_breakpoint code is a complete disaster so my preference would be to
rip out the perf part and just implement something directly in ptrace,
but it's a pretty horrible job". Though Will commented this on arm
architecture, but the comment also can apply on arm64 architecture.
For complete information, I searched online and found a few years back,
Wang Nan sent one patch 'arm64: Store breakpoint single step state into
pstate' [2]; the patch tried to resolve this issue by avoiding single
stepping in signal handler and defer to enable the signal stepping when
return to __test_function(). The fixing was not merged due to the
concern for missing to handle different usage cases.
Based on the info, the most feasible way is to skip Perf breakpoint
signal testing for arm64 and this could avoid the duplicate
investigation efforts when people see the failure. This patch skips
this case on arm64 platform, which is same with arm architecture.
[1] https://lkml.org/lkml/2018/11/15/205
[2] https://lkml.org/lkml/2015/12/23/477
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Brajeswar Ghosh <brajeswar.linux@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Will Deacon <will@kernel.org>
Link: http://lore.kernel.org/lkml/20191018085531.6348-3-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.