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Up until now, the function graph tracer could only have a single user attached to it. If another user tried to attach to the function graph tracer while one was already attached, it would fail. Allowing function graph tracer to have more than one user has been asked for since 2009, but it required a rewrite to the logic to pull it off so it never happened. Until now! There's three systems that trace the return of a function. That is kretprobes, function graph tracer, and BPF. kretprobes and function graph tracing both do it similarly. The difference is that kretprobes uses a shadow stack per callback and function graph tracer creates a shadow stack for all tasks. The function graph tracer method makes it possible to trace the return of all functions. As kretprobes now needs that feature too, allowing it to use function graph tracer was needed. BPF also wants to trace the return of many probes and its method doesn't scale either. Having it use function graph tracer would improve that. By allowing function graph tracer to have multiple users allows both kretprobes and BPF to use function graph tracer in these cases. This will allow kretprobes code to be removed in the future as it's version will no longer be needed. Note, function graph tracer is only limited to 16 simultaneous users, due to shadow stack size and allocated slots. -----BEGIN PGP SIGNATURE----- iIoEABYIADIWIQRRSw7ePDh/lE+zeZMp5XQQmuv6qgUCZpbWlxQccm9zdGVkdEBn b29kbWlzLm9yZwAKCRAp5XQQmuv6qgtvAP9jxmgEiEhz4Bpe1vRKVSMYK6ozXHTT 7MFKRMeQqQ8zeAEA2sD5Zrt9l7zKzg0DFpaDLgc3/yh14afIDxzTlIvkmQ8= =umuf -----END PGP SIGNATURE----- Merge tag 'ftrace-v6.11' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull ftrace updates from Steven Rostedt: "Rewrite of function graph tracer to allow multiple users Up until now, the function graph tracer could only have a single user attached to it. If another user tried to attach to the function graph tracer while one was already attached, it would fail. Allowing function graph tracer to have more than one user has been asked for since 2009, but it required a rewrite to the logic to pull it off so it never happened. Until now! There's three systems that trace the return of a function. That is kretprobes, function graph tracer, and BPF. kretprobes and function graph tracing both do it similarly. The difference is that kretprobes uses a shadow stack per callback and function graph tracer creates a shadow stack for all tasks. The function graph tracer method makes it possible to trace the return of all functions. As kretprobes now needs that feature too, allowing it to use function graph tracer was needed. BPF also wants to trace the return of many probes and its method doesn't scale either. Having it use function graph tracer would improve that. By allowing function graph tracer to have multiple users allows both kretprobes and BPF to use function graph tracer in these cases. This will allow kretprobes code to be removed in the future as it's version will no longer be needed. Note, function graph tracer is only limited to 16 simultaneous users, due to shadow stack size and allocated slots" * tag 'ftrace-v6.11' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (49 commits) fgraph: Use str_plural() in test_graph_storage_single() function_graph: Add READ_ONCE() when accessing fgraph_array[] ftrace: Add missing kerneldoc parameters to unregister_ftrace_direct() function_graph: Everyone uses HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, remove it function_graph: Fix up ftrace_graph_ret_addr() function_graph: Make fgraph_update_pid_func() a stub for !DYNAMIC_FTRACE function_graph: Rename BYTE_NUMBER to CHAR_NUMBER in selftests fgraph: Remove some unused functions ftrace: Hide one more entry in stack trace when ftrace_pid is enabled function_graph: Do not update pid func if CONFIG_DYNAMIC_FTRACE not enabled function_graph: Make fgraph_do_direct static key static ftrace: Fix prototypes for ftrace_startup/shutdown_subops() ftrace: Assign RCU list variable with rcu_assign_ptr() ftrace: Assign ftrace_list_end to ftrace_ops_list type cast to RCU ftrace: Declare function_trace_op in header to quiet sparse warning ftrace: Add comments to ftrace_hash_move() and friends ftrace: Convert "inc" parameter to bool in ftrace_hash_rec_update_modify() ftrace: Add comments to ftrace_hash_rec_disable/enable() ftrace: Remove "filter_hash" parameter from __ftrace_hash_rec_update() ftrace: Rename dup_hash() and comment it ... |
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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.