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When FEAT_SPE_PBT is implemented, the previous branch target address (named as PBT) before the sampled operation, will be recorded. This commit first introduces a 'prev_br_tgt' field in the record for saving the PBT address in the decoder. If the current operation is a branch instruction, by combining with PBT, it can create a chain with two consecutive branches. As the branch stack stores branches in descending order, meaning a newer branch is stored in a lower entry in the stack. Arm SPE stores the latest branch in the first entry of branch stack, and the previous branch coming from PBT is stored into the second entry. Otherwise, if current operation is not a branch, the last branch will be saved for PBT only. PBT lacks associated information such as branch source address, branch type, and events. The branch entry fills zeros for the corresponding fields and only set its target address. After: perf script -f --itrace=bl -F flags,addr,brstack jcc ffff800080187914 0xffff8000801878fc/0xffff800080187914/P/-/-/1/COND/- 0x0/0xffff8000801878f8/-/-/-/0//- jcc ffff8000802d12d8 0xffff8000802d12f8/0xffff8000802d12d8/P/-/-/1/COND/- 0x0/0xffff8000802d12ec/-/-/-/0//- jcc ffff8000813fe200 0xffff8000813fe20c/0xffff8000813fe200/P/-/-/1/COND/- 0x0/0xffff8000813fe200/-/-/-/0//- jcc ffff8000813fe200 0xffff8000813fe20c/0xffff8000813fe200/P/-/-/1/COND/- 0x0/0xffff8000813fe200/-/-/-/0//- jmp ffff800081410980 0xffff800081419108/0xffff800081410980/P/-/-/1//- 0x0/0xffff800081419104/-/-/-/0//- return ffff80008036e064 0xffff80008141ba84/0xffff80008036e064/P/-/-/1/RET/- 0x0/0xffff80008141ba60/-/-/-/0//- jcc ffff8000803d54f0 0xffff8000803d54e8/0xffff8000803d54f0/P/-/-/1/COND/- 0x0/0xffff8000803d54e0/-/-/-/0//- jmp ffff80008015e468 0xffff8000803d46dc/0xffff80008015e468/P/-/-/1//- 0x0/0xffff8000803d46c8/-/-/-/0//- jmp ffff8000806e2d50 0xffff80008040f710/0xffff8000806e2d50/P/-/-/1//- 0x0/0xffff80008040f6e8/-/-/-/0//- jcc ffff800080721704 0xffff8000807216b4/0xffff800080721704/P/-/-/1/COND/- 0x0/0xffff8000807216ac/-/-/-/0//- Reviewed-by: Ian Rogers <irogers@google.com> Reviewed-by: James Clark <james.clark@linaro.org> Signed-off-by: Leo Yan <leo.yan@arm.com> Link: https://lore.kernel.org/r/20250304111240.3378214-13-leo.yan@arm.com Signed-off-by: Namhyung Kim <namhyung@kernel.org> |
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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 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.