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contrib/plugins: extend execlog to track register changes

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With the new plugin register API we can now track changes to register
values. Currently the implementation is fairly dumb which will slow
down if a large number of register values are being tracked. This
could be improved by only instrumenting instructions which mention
registers we are interested in tracking.

Example usage:

  ./qemu-aarch64 -D plugin.log -d plugin \
     -cpu max,sve256=on \
     -plugin contrib/plugins/libexeclog.so,reg=sp,reg=z\* \
     ./tests/tcg/aarch64-linux-user/sha512-sve

will display in the execlog any changes to the stack pointer (sp) and
the SVE Z registers.

As testing registers every instruction will be quite a heavy operation
there is an additional flag which attempts to optimise the register
tracking by only instrumenting instructions which are likely to change
its value. This relies on the QEMU disassembler showing up the register
names in disassembly so is an explicit opt-in.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Cc: Akihiko Odaki <akihiko.odaki@daynix.com>
Based-On:  <20231025093128.33116-19-akihiko.odaki@daynix.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240227144335.1196131-27-alex.bennee@linaro.org>
This commit is contained in:
Alex Bennée 2024-02-27 14:43:32 +00:00
parent 9e096a76c7
commit af6e4e0a22
2 changed files with 281 additions and 52 deletions
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17
docs/devel/tcg-plugins.rst
View file

@ -497,6 +497,22 @@ arguments if required::
$ qemu-system-arm $(QEMU_ARGS) \
-plugin ./contrib/plugins/libexeclog.so,ifilter=st1w,afilter=0x40001808 -d plugin
This plugin can also dump registers when they change value. Specify the name of the
registers with multiple ``reg`` options. You can also use glob style matching if you wish::
$ qemu-system-arm $(QEMU_ARGS) \
-plugin ./contrib/plugins/libexeclog.so,reg=\*_el2,reg=sp -d plugin
Be aware that each additional register to check will slow down
execution quite considerably. You can optimise the number of register
checks done by using the rdisas option. This will only instrument
instructions that mention the registers in question in disassembly.
This is not foolproof as some instructions implicitly change
instructions. You can use the ifilter to catch these cases:
$ qemu-system-arm $(QEMU_ARGS) \
-plugin ./contrib/plugins/libexeclog.so,ifilter=msr,ifilter=blr,reg=x30,reg=\*_el1,rdisas=on
- contrib/plugins/cache.c
Cache modelling plugin that measures the performance of a given L1 cache
@ -583,4 +599,3 @@ The following API is generated from the inline documentation in
include the full kernel-doc annotations.
.. kernel-doc:: include/qemu/qemu-plugin.h