For debugging, it might be useful to run the debug trap
instruction to break into the debugger. To detect the debugger
presence, the kernel provides the `/proc/self/status` pseudo-file
that needs to be searched for the "TracerPid:" string.

Provide a prctl command that returns the PID of the tracer if any.
That allows for much simpler logic in the user land, and makes it
possible to detect tracer presence even if PROC_FS is not enabled.

As an example where this might be useful, one might refer to
the standard C++ and Rust libraries. See these links for the details:

* https://en.cppreference.com/w/cpp/utility/breakpoint_if_debugging
* https://lists.llvm.org/pipermail/libcxx-commits/2024-May/083574.html
* https://patchwork-proxy.ozlabs.org/project/gcc/patch/20240601102446.878286-1-jwakely@redhat.com/#3321542
* https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2546r0.html
* https://github.com/rust-lang/rust/pull/129019

Roman Kisel (1):
  ptrace: Get tracer PID without reliance on the proc FS

 include/uapi/linux/ptrace.h |  1 +
 kernel/ptrace.c             | 11 ++++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)


base-commit: ad618736883b8970f66af799e34007475fe33a68
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2.34.1