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Huacai Chen d6af2c7639 LoongArch: Fix callchain parse error with kernel tracepoint events again 
With commit d3119bc985 ("LoongArch: Fix callchain parse error with
kernel tracepoint events"), perf can parse kernel callchain, but not
complete and sometimes maybe error. The reason is LoongArch's unwinders
(guess, prologue and orc) don't really need fp (i.e., regs[22]), and
they use sp (i.e., regs[3]) as the frame address rather than the current
stack pointer.

Fix that by removing the assignment of regs[22], and instead assign the
__builtin_frame_address(0) to regs[3].

Without fix:

  Children      Self  Command        Shared Object      Symbol
  ........  ........  .............  .................  ................
  33.91%    33.91%    swapper        [kernel.vmlinux]   [k] __schedule
            |
            |--33.04%--__schedule
            |
             --0.87%--__arch_cpu_idle
                       __schedule

With this fix:

  Children      Self  Command        Shared Object      Symbol
  ........  ........  .............  .................  ................
  31.16%    31.16%    swapper        [kernel.vmlinux]   [k] __schedule
            |
            |--20.63%--smpboot_entry
            |          cpu_startup_entry
            |          schedule_idle
            |          __schedule
            |
             --10.53%--start_kernel
                       cpu_startup_entry
                       schedule_idle
                       __schedule

Fixes: d3119bc985 ("LoongArch: Fix callchain parse error with kernel tracepoint events")
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
History 2024-05-14 12:24:18 +08:00
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README 

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.