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Normally exception packets don't directly output a branch sample, but
if they're the last record in a buffer then they will. Because they
don't have addresses set we'll see the placeholder value
CS_ETM_INVAL_ADDR (0xdeadbeef) in the output.
Since commit 6035b6804b ("perf cs-etm: Support dummy address value for
CS_ETM_TRACE_ON packet") we've used 0 as an externally visible "not set"
address value. For consistency reasons and to not make exceptions look
like an error, change them to use 0 too.
This is particularly visible when doing userspace only tracing because
trace is disabled when jumping to the kernel, causing the flush and then
forcing the last exception packet to be emitted as a branch. With kernel
trace included, there is no flush so exception packets don't generate
samples until the next range packet and they'll pick up the correct
address.
Before:
$ perf record -e cs_etm//u -- stress -i 1 -t 1
$ perf script -F comm,ip,addr,flags
stress syscall ffffb7eedbc0 => deadbeefdeadbeef
stress syscall ffffb7f14a14 => deadbeefdeadbeef
stress syscall ffffb7eedbc0 => deadbeefdeadbeef
After:
stress syscall ffffb7eedbc0 => 0
stress syscall ffffb7f14a14 => 0
stress syscall ffffb7eedbc0 => 0
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: James Clark <james.clark@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Leo Yan <leo.yan@linux.dev>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: coresight@lists.linaro.org
Cc: gankulkarni@os.amperecomputing.com
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20240722152756.59453-2-james.clark@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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 reStructuredText 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.