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bdf8eafbf7
When analysing a stacktrace it can be useful to know where an unwound PC came from, as in some situations certain sources may be suspect or known to be unreliable. In future it would also be useful to track this so that certain unwind steps can be performed in a stateful manner. For example when unwinding across an exception boundary, we'd ideally unwind pt_regs::pc, then pt_regs::lr, then the next frame record. This patch adds an enumerated set of unwind sources, tracks this during the unwind, and updates dump_backtrace() to log these for interesting unwind steps. The interesting sources recorded are: "C" - the PC came from the caller of an unwind function. "T" - the PC came from thread_saved_pc() for a blocked task. "P" - the PC came from a pt_regs::pc. "U" - the PC came from an unknown source (indicates an unwinder error). ... with nothing recorded when the PC came from a frame_record::pc as this is the vastly common case and logging this would make it difficult to spot the more interesting cases. For example, when triggering a backtrace via magic-sysrq + L, the CPU handling the sysrq will have a backtrace whose first element is the caller (C) of dump_backtrace(): | Call trace: | show_stack+0x18/0x30 (C) | dump_stack_lvl+0x60/0x80 | dump_stack+0x18/0x24 | nmi_cpu_backtrace+0xfc/0x140 | ... ... and other CPUs will have a backtrace whose first element is their pt_regs::pc (P) at the instant the backtrace IPI was taken: | Call trace: | _raw_spin_unlock_irqrestore+0x8/0x50 (P) | wake_up_process+0x18/0x24 | process_timeout+0x14/0x20 | call_timer_fn.isra.0+0x24/0x80 | ... Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Mark Brown <broonie@kernel.org> Reviewed-by: Miroslav Benes <mbenes@suse.cz> Reviewed-by: Puranjay Mohan <puranjay12@gmail.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Josh Poimboeuf <jpoimboe@kernel.org> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20241017092538.1859841-8-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.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 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.