Lines Matching refs:the
8 Here we will cover the architecture pieces that the common function tracing
13 want more explanation of a feature in terms of common code, review the common
17 their kernel should make it all the way to dynamic ftrace support.
31 You will need to implement the mcount and the ftrace_stub functions.
38 We'll make the assumption below that the symbol is "mcount" just to keep things
39 nice and simple in the examples.
41 Keep in mind that the ABI that is in effect inside of the mcount function is
45 is a major issue at this point, especially in relation to the location of the
47 how glibc has implemented the mcount function for your architecture. It might
50 The mcount function should check the function pointer ftrace_trace_function
52 so return immediately. If it isn't, then call that function in the same way
53 the mcount function normally calls __mcount_internal -- the first argument is
54 the "frompc" while the second argument is the "selfpc" (adjusted to remove the
55 size of the mcount call that is embedded in the function).
57 For example, if the function foo() calls bar(), when the bar() function calls
58 mcount(), the arguments mcount() will pass to the tracer are:
59 "frompc" - the address bar() will use to return to foo()
60 "selfpc" - the address bar() (with mcount() size adjustment)
63 optimizing for the default case of no tracer will help the smooth running of
64 your system when tracing is disabled. So the start of the mcount function is
65 typically the bare minimum with checking things before returning. That also
66 means the code flow should usually be kept linear (i.e. no branching in the nop
91 /* save all state needed by the ABI (see paragraph above) */
97 /* restore all state needed by the ABI */
108 Deep breath ... time to do some real work. Here you will need to update the
110 some functions to save (hijack) and restore the return address.
112 The mcount function should check the function pointers ftrace_graph_return
114 ftrace_graph_entry_stub). If either of those is not set to the relevant stub
115 function, call the arch-specific function ftrace_graph_caller which in turn
116 calls the arch-specific function prepare_ftrace_return. Neither of these
118 consistent across the architecture ports -- easier to compare & contrast
122 passed to ftrace_trace_function. The second argument "selfpc" is the same,
123 but the first argument should be a pointer to the "frompc". Typically this is
124 located on the stack. This allows the function to hijack the return address
125 temporarily to have it point to the arch-specific function return_to_handler.
126 That function will simply call the common ftrace_return_to_handler function and
127 that will return the original return address with which you can return to the
130 Here is the updated mcount pseudo code:
148 Here is the pseudo code for the new ftrace_graph_caller assembly function:
152 /* save all state needed by the ABI */
159 /* restore all state needed by the ABI */
163 For information on how to implement prepare_ftrace_return(), simply look at the
164 x86 version (the frame pointer passing is optional; see the next section for
165 more information). The only architecture-specific piece in it is the setup of
166 the fault recovery table (the asm(...) code). The rest should be the same
169 Here is the pseudo code for the new return_to_handler assembly function. Note
170 that the ABI that applies here is different from what applies to the mcount
171 code. Since you are returning from a function (after the epilogue), you might
178 /* save all state needed by the ABI (see paragraph above) */
182 /* restore all state needed by the ABI */
193 An arch may pass in a unique value (frame pointer) to both the entering and
194 exiting of a function. On exit, the value is compared and if it does not
195 match, then it will panic the kernel. This is largely a sanity check for bad
196 code generation with gcc. If gcc for your port sanely updates the frame
200 that calls prepare_ftrace_return(), pass the frame pointer as the 3rd argument.
201 Then in the C version of that function, do what the x86 port does and pass it
204 Similarly, when you call ftrace_return_to_handler(), pass it the frame pointer.
218 You need very few things to get the syscalls tracing in an arch.
221 - Have a NR_syscalls variable in <asm/unistd.h> that provides the number
222 of syscalls supported by the arch.
223 - Support the TIF_SYSCALL_TRACEPOINT thread flags.
224 - Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace
225 in the ptrace syscalls tracing path.
226 - If the system call table on this arch is more complicated than a simple array
227 of addresses of the system calls, implement an arch_syscall_addr to return
228 the address of a given system call.
229 - If the symbol names of the system calls do not match the function names on
231 implement arch_syscall_match_sym_name with the appropriate logic to return
232 true if the function name corresponds with the symbol name.
239 See scripts/recordmcount.pl for more info. Just fill in the arch-specific
240 details for how to locate the addresses of mcount call sites via objdump.
250 Once those are out of the way, you will need to implement:
268 Define MCOUNT_ADDR as the address of your mcount symbol similar to:
273 You will also need the helper function ftrace_call_adjust(). Most people
281 Lastly you will need the custom dyn_arch_ftrace structure. If you need
282 some extra state when runtime patching arbitrary call sites, this is the
288 With the header out of the way, we can fill out the assembly code. While we
290 stub function. This is because the mcount() will only be used during boot
292 the guts of the old mcount() will be used to create a new ftrace_caller()
293 function. Because the two are hard to merge, it will most likely be a lot
295 the ftrace_stub() as that will now be inlined in ftrace_caller().
307 /* save all state needed by the ABI (see paragraph above) */
315 /* restore all state needed by the ABI */
324 active at a time, we will patch the ftrace_caller() function itself to call the
325 specific tracer in question. That is the point of the ftrace_call label.
327 With that in mind, let's move on to the C code that will actually be doing the
329 order to make it through the next section.
332 to initialize some state, this is the time to do that. Otherwise, this simple
341 functions. The first is used to turn the mcount call site into a nop (which
343 used to turn the mcount call site into a call to an arbitrary location (but
344 typically that is ftracer_caller()). See the general function definition in
345 linux/ftrace.h for the functions:
348 The rec->ip value is the address of the mcount call site that was collected
349 by the scripts/recordmcount.pl during build time.
351 The last function is used to do runtime patching of the active tracer. This
352 will be modifying the assembly code at the location of the ftrace_call symbol
353 inside of the ftrace_caller() function. So you should have sufficient padding
354 at that location to support the new function calls you'll be inserting. Some
356 "branch" type instruction. Specifically, the function is:
375 - add a nop stub after the ftrace_call location named ftrace_graph_call;
377 - update ftrace_graph_caller() to work with being called by the new
379 - ftrace_enable_ftrace_graph_caller() will runtime patch the
381 - ftrace_disable_ftrace_graph_caller() will runtime patch the