Documentation/trace/ftrace-design.rst

12 ------------
20 ftrace.txt file.
23 their kernel should make it all the way to dynamic ftrace support.
27 -------------
29 Ftrace relies on these features being implemented:
30   - STACKTRACE_SUPPORT - implement save_stack_trace()
31   - TRACE_IRQFLAGS_SUPPORT - implement include/asm/irqflags.h
35 --------------------
43 	$ echo 'main(){}' | gcc -x c -S -o - - -pg | grep mcount
56 be (semi-)relevant.
61 the mcount function normally calls __mcount_internal -- the first argument is
63 size of the mcount call that is embedded in the function).
68   - "frompc" - the address bar() will use to return to foo()
69   - "selfpc" - the address bar() (with mcount() size adjustment)
103 		unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
117 --------------------------
120 mcount function to check ftrace graph function pointers, as well as implement
126 function, call the arch-specific function ftrace_graph_caller which in turn
127 calls the arch-specific function prepare_ftrace_return.  Neither of these
129 consistent across the architecture ports -- easier to compare & contrast
136 temporarily to have it point to the arch-specific function return_to_handler.
168 		unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
169 		/* passing frame pointer up is optional -- see below */
178 more information).  The only architecture-specific piece in it is the setup of
205 ---------------------------
221 --------------------------------
228 Adding support for it is easy: just define the macro in asm/ftrace.h and
233 ------------------------
237   - Support HAVE_ARCH_TRACEHOOK (see arch/Kconfig).
238   - Have a NR_syscalls variable in <asm/unistd.h> that provides the number
240   - Support the TIF_SYSCALL_TRACEPOINT thread flags.
241   - Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace
243   - If the system call table on this arch is more complicated than a simple array
246   - If the symbol names of the system calls do not match the function names on
247     this arch, define ARCH_HAS_SYSCALL_MATCH_SYM_NAME in asm/ftrace.h and
250   - Tag this arch as HAVE_SYSCALL_TRACEPOINTS.
254 -------------------------
256 See scripts/recordmcount.pl for more info.  Just fill in the arch-specific
258 This option doesn't make much sense without also implementing dynamic ftrace.
262 -------------------
268 	- asm/ftrace.h:
269 		- MCOUNT_ADDR
270 		- ftrace_call_adjust()
271 		- struct dyn_arch_ftrace{}
272 	- asm code:
273 		- mcount() (new stub)
274 		- ftrace_caller()
275 		- ftrace_call()
276 		- ftrace_stub()
277 	- C code:
278 		- ftrace_dyn_arch_init()
279 		- ftrace_make_nop()
280 		- ftrace_make_call()
281 		- ftrace_update_ftrace_func()
283 First you will need to fill out some arch details in your asm/ftrace.h.
312 did already create a mcount() function earlier, dynamic ftrace only wants a
333 		unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
368 linux/ftrace.h for the functions::
373 The rec->ip value is the address of the mcount call site that was collected
387 ------------------------------------------------
389 The function grapher needs a few tweaks in order to work with dynamic ftrace.
392 	- update:
393 		- ftrace_caller()
394 		- ftrace_graph_call()
395 		- ftrace_graph_caller()
396 	- implement:
397 		- ftrace_enable_ftrace_graph_caller()
398 		- ftrace_disable_ftrace_graph_caller()
404 	- add a nop stub after the ftrace_call location named ftrace_graph_call;
406 	- update ftrace_graph_caller() to work with being called by the new
408 	- ftrace_enable_ftrace_graph_caller() will runtime patch the
410 	- ftrace_disable_ftrace_graph_caller() will runtime patch the