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a52f6043a2
Add support for DYNAMIC_FTRACE_WITH_DIRECT_CALLS similar to the arm64 implementation. ftrace direct calls allow custom trampolines to be called into directly from function ftrace call sites, bypassing the ftrace trampoline completely. This functionality is currently utilized by BPF trampolines to hook into kernel function entries. Since we have limited relative branch range, we support ftrace direct calls through support for DYNAMIC_FTRACE_WITH_CALL_OPS. In this approach, ftrace trampoline is not entirely bypassed. Rather, it is re-purposed into a stub that reads direct_call field from the associated ftrace_ops structure and branches into that, if it is not NULL. For this, it is sufficient if we can ensure that the ftrace trampoline is reachable from all traceable functions. When multiple ftrace_ops are associated with a call site, we utilize a call back to set pt_regs->orig_gpr3 that can then be tested on the return path from the ftrace trampoline to branch into the direct caller. Signed-off-by: Naveen N Rao <naveen@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://patch.msgid.link/20241030070850.1361304-16-hbathini@linux.ibm.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.