lwn.git/arch/powerpc/kernel/ftrace.c, branch docs-6.9

powerpc: Split ftrace bits into a separate file

2017-04-27T12:20:29+00:00

entry_*.S now includes a lot more than just kernel entry/exit code. As a first step at cleaning this up, let's split out the ftrace bits into separate files. Also move all related tracing code into a new trace/ subdirectory. No functional changes. Suggested-by: Michael Ellerman Signed-off-by: Naveen N. Rao Signed-off-by: Michael Ellerman

powerpc/ftrace: Add prototype for prepare_ftrace_return()

2017-03-20T08:02:49+00:00

Sparse emits a warning: symbol 'prepare_ftrace_return' was not declared. Should it be static? prepare_ftrace_return() is called from assembler and should not be static. Add a prototype for it to asm-prototypes.h and include that in ftrace.c. Signed-off-by: Tobin C. Harding Signed-off-by: Michael Ellerman

powerpc/ftrace: Fix the comments for ftrace_modify_code

2016-12-03T11:10:15+00:00

There is no need to worry about module and __init text disappearing case, because that ftrace has a module notifier that is called when a module is being unloaded and before the text goes away and this code grabs the ftrace_lock mutex and removes the module functions from the ftrace list, such that it will no longer do any modifications to that module's text, the update to make functions be traced or not is done under the ftrace_lock mutex as well. And by now, __init section codes should not been modified by ftrace, because it is black listed in recordmcount.c and ignored by ftrace. Suggested-by: Steven Rostedt Signed-off-by: Li Bin Signed-off-by: Michael Ellerman

ftrace: Add return address pointer to ftrace_ret_stack

2016-08-24T10:15:14+00:00

Storing this value will help prevent unwinders from getting out of sync with the function graph tracer ret_stack. Now instead of needing a stateful iterator, they can compare the return address pointer to find the right ret_stack entry. Note that an array of 50 ftrace_ret_stack structs is allocated for every task. So when an arch implements this, it will add either 200 or 400 bytes of memory usage per task (depending on whether it's a 32-bit or 64-bit platform). Signed-off-by: Josh Poimboeuf Acked-by: Steven Rostedt Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Byungchul Park Cc: Denys Vlasenko Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Nilay Vaish Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/a95cfcc39e8f26b89a430c56926af0bb217bc0a1.1471607358.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar

powerpc/ftrace: Separate the heuristics for checking call sites

2016-07-21T10:10:37+00:00

In __ftrace_make_nop() (the 64-bit version), we have code to deal with two ftrace ABIs. There is the original ABI, which looks mostly like a function call, and then the mprofile-kernel ABI which is just a branch. The code tries to handle both cases, by looking for the presence of a load to restore the TOC pointer (PPC_INST_LD_TOC). If we detect the TOC load, we assume the call site is for an mcount() call using the old ABI. That means we patch the mcount() call with a b +8, to branch over the TOC load. However if the kernel was built with mprofile-kernel, then there will never be a call site using the original ftrace ABI. If for some reason we do see a TOC load, then it's there for a good reason, and we should not jump over it. So split the code, using the existing CC_USING_MPROFILE_KERNEL. Kernels built with mprofile-kernel will only look for, and expect, the new ABI, and similarly for the original ABI. Signed-off-by: Michael Ellerman

powerpc: Define and use PPC64_ELF_ABI_v2/v1

2016-06-14T03:58:27+00:00

We're approaching 20 locations where we need to check for ELF ABI v2. That's fine, except the logic is a bit awkward, because we have to check that _CALL_ELF is defined and then what its value is. So check it once in asm/types.h and define PPC64_ELF_ABI_v2 when ELF ABI v2 is detected. We also have a few places where what we're really trying to check is that we are using the 64-bit v1 ABI, ie. function descriptors. So also add a #define for that, which simplifies several checks. Signed-off-by: Naveen N. Rao Signed-off-by: Michael Ellerman

ftrace: Match dot symbols when searching functions on ppc64

2016-04-26T23:47:29+00:00

In the ppc64 big endian ABI, function symbols point to function descriptors. The symbols which point to the function entry points have a dot in front of the function name. Consequently, when the ftrace filter mechanism searches for the symbol corresponding to an entry point address, it gets the dot symbol. As a result, ftrace filter users have to be aware of this ABI detail on ppc64 and prepend a dot to the function name when setting the filter. The perf probe command insulates the user from this by ignoring the dot in front of the symbol name when matching function names to symbols, but the sysfs interface does not. This patch makes the ftrace filter mechanism do the same when searching symbols. Fixes the following failure in ftracetest's kprobe_ftrace.tc: .../kprobe_ftrace.tc: line 9: echo: write error: Invalid argument That failure is on this line of kprobe_ftrace.tc: echo _do_fork > set_ftrace_filter This is because there's no _do_fork entry in the functions list: # cat available_filter_functions | grep _do_fork ._do_fork This change introduces no regressions on the perf and ftracetest testsuite results. Cc: Steven Rostedt Cc: Ingo Molnar Cc: Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Thiago Jung Bauermann Acked-by: Steven Rostedt Signed-off-by: Michael Ellerman

powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI

2016-03-07T03:53:55+00:00

The gcc switch -mprofile-kernel defines a new ABI for calling _mcount() very early in the function with minimal overhead. Although mprofile-kernel has been available since GCC 3.4, there were bugs which were only fixed recently. Currently it is known to work in GCC 4.9, 5 and 6. Additionally there are two possible code sequences generated by the flag, the first uses mflr/std/bl and the second is optimised to omit the std. Currently only gcc 6 has the optimised sequence. This patch supports both sequences. Initial work started by Vojtech Pavlik, used with permission. Key changes: - rework _mcount() to work for both the old and new ABIs. - implement new versions of ftrace_caller() and ftrace_graph_caller() which deal with the new ABI. - updates to __ftrace_make_nop() to recognise the new mcount calling sequence. - updates to __ftrace_make_call() to recognise the nop'ed sequence. - implement ftrace_modify_call(). - updates to the module loader to surpress the toc save in the module stub when calling mcount with the new ABI. Reviewed-by: Balbir Singh Signed-off-by: Torsten Duwe Signed-off-by: Michael Ellerman

powerpc/ftrace: Use generic ftrace_modify_all_code()

2016-03-07T03:53:54+00:00

Convert powerpc's arch_ftrace_update_code() from its own version to use the generic default functionality (without stop_machine -- our instructions are properly aligned and the replacements atomic). With this we gain error checking and the much-needed function_trace_op handling. Reviewed-by: Balbir Singh Reviewed-by: Kamalesh Babulal Signed-off-by: Torsten Duwe Signed-off-by: Michael Ellerman

powerpc/module: Mark module stubs with a magic value

2016-03-07T03:53:53+00:00

When a module is loaded, calls out to the kernel go via a stub which is generated at runtime. One of these stubs is used to call _mcount(), which is the default target of tracing calls generated by the compiler with -pg. If dynamic ftrace is enabled (which it typically is), another stub is used to call ftrace_caller(), which is the target of tracing calls when ftrace is actually active. ftrace then wants to disable the calls to _mcount() at module startup, and enable/disable the calls to ftrace_caller() when enabling/disabling tracing - all of these it does by patching the code. As part of that code patching, the ftrace code wants to confirm that the branch it is about to modify, is in fact a call to a module stub which calls _mcount() or ftrace_caller(). Currently it does that by inspecting the instructions and confirming they are what it expects. Although that works, the code to do it is pretty intricate because it requires lots of knowledge about the exact format of the stub. We can make that process easier by marking the generated stubs with a magic value, and then looking for that magic value. Altough this is not as rigorous as the current method, I believe it is sufficient in practice. Reviewed-by: Balbir Singh Reviewed-by: Torsten Duwe Signed-off-by: Michael Ellerman