3 files changed, 149 insertions, 132 deletions

diff --git a/Documentation/trace/ftrace-design.txt b/Documentation/trace/ftrace-design.txt
index f1f81afee8a0..dc52bd442c92 100644
--- a/Documentation/trace/ftrace-design.txt
+++ b/Documentation/trace/ftrace-design.txt
@@ -13,6 +13,9 @@ Note that this focuses on architecture implementation details only.  If you
 want more explanation of a feature in terms of common code, review the common
 ftrace.txt file.
 
+Ideally, everyone who wishes to retain performance while supporting tracing in
+their kernel should make it all the way to dynamic ftrace support.
+
 
 Prerequisites
 -------------
@@ -215,7 +218,7 @@ An arch may pass in a unique value (frame pointer) to both the entering and
 exiting of a function.  On exit, the value is compared and if it does not
 match, then it will panic the kernel.  This is largely a sanity check for bad
 code generation with gcc.  If gcc for your port sanely updates the frame
-pointer under different opitmization levels, then ignore this option.
+pointer under different optimization levels, then ignore this option.
 
 However, adding support for it isn't terribly difficult.  In your assembly code
 that calls prepare_ftrace_return(), pass the frame pointer as the 3rd argument.
@@ -234,7 +237,7 @@ If you can't trace NMI functions, then skip this option.
 
 
 HAVE_SYSCALL_TRACEPOINTS
----------------------
+------------------------
 
 You need very few things to get the syscalls tracing in an arch.
 
@@ -250,12 +253,152 @@ You need very few things to get the syscalls tracing in an arch.
 HAVE_FTRACE_MCOUNT_RECORD
 -------------------------
 
-See scripts/recordmcount.pl for more info.
+See scripts/recordmcount.pl for more info.  Just fill in the arch-specific
+details for how to locate the addresses of mcount call sites via objdump.
+This option doesn't make much sense without also implementing dynamic ftrace.
 
+
+HAVE_DYNAMIC_FTRACE
+-------------------
+
+You will first need HAVE_FTRACE_MCOUNT_RECORD and HAVE_FUNCTION_TRACER, so
+scroll your reader back up if you got over eager.
+
+Once those are out of the way, you will need to implement:
+        - asm/ftrace.h:
+                - MCOUNT_ADDR
+                - ftrace_call_adjust()
+                - struct dyn_arch_ftrace{}
+        - asm code:
+                - mcount() (new stub)
+                - ftrace_caller()
+                - ftrace_call()
+                - ftrace_stub()
+        - C code:
+                - ftrace_dyn_arch_init()
+                - ftrace_make_nop()
+                - ftrace_make_call()
+                - ftrace_update_ftrace_func()
+
+First you will need to fill out some arch details in your asm/ftrace.h.
+
+Define MCOUNT_ADDR as the address of your mcount symbol similar to:
+        #define MCOUNT_ADDR ((unsigned long)mcount)
+Since no one else will have a decl for that function, you will need to:
+        extern void mcount(void);
+
+You will also need the helper function ftrace_call_adjust().  Most people
+will be able to stub it out like so:
+        static inline unsigned long ftrace_call_adjust(unsigned long addr)
+        {
+                return addr;
+        }
 <details to be filled>
 
+Lastly you will need the custom dyn_arch_ftrace structure.  If you need
+some extra state when runtime patching arbitrary call sites, this is the
+place.  For now though, create an empty struct:
+        struct dyn_arch_ftrace {
+                /* No extra data needed */
+        };
+
+With the header out of the way, we can fill out the assembly code.  While we
+did already create a mcount() function earlier, dynamic ftrace only wants a
+stub function.  This is because the mcount() will only be used during boot
+and then all references to it will be patched out never to return.  Instead,
+the guts of the old mcount() will be used to create a new ftrace_caller()
+function.  Because the two are hard to merge, it will most likely be a lot
+easier to have two separate definitions split up by #ifdefs.  Same goes for
+the ftrace_stub() as that will now be inlined in ftrace_caller().
+
+Before we get confused anymore, let's check out some pseudo code so you can
+implement your own stuff in assembly:
 
-HAVE_DYNAMIC_FTRACE
----------------------
+void mcount(void)
+{
+        return;
+}
+
+void ftrace_caller(void)
+{
+        /* implement HAVE_FUNCTION_TRACE_MCOUNT_TEST if you desire */
+
+        /* save all state needed by the ABI (see paragraph above) */
+
+        unsigned long frompc = ...;
+        unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE;
+
+ftrace_call:
+        ftrace_stub(frompc, selfpc);
+
+        /* restore all state needed by the ABI */
+
+ftrace_stub:
+        return;
+}
+
+This might look a little odd at first, but keep in mind that we will be runtime
+patching multiple things.  First, only functions that we actually want to trace
+will be patched to call ftrace_caller().  Second, since we only have one tracer
+active at a time, we will patch the ftrace_caller() function itself to call the
+specific tracer in question.  That is the point of the ftrace_call label.
+
+With that in mind, let's move on to the C code that will actually be doing the
+runtime patching.  You'll need a little knowledge of your arch's opcodes in
+order to make it through the next section.
+
+Every arch has an init callback function.  If you need to do something early on
+to initialize some state, this is the time to do that.  Otherwise, this simple
+function below should be sufficient for most people:
+
+int __init ftrace_dyn_arch_init(void *data)
+{
+        /* return value is done indirectly via data */
+        *(unsigned long *)data = 0;
+
+        return 0;
+}
+
+There are two functions that are used to do runtime patching of arbitrary
+functions.  The first is used to turn the mcount call site into a nop (which
+is what helps us retain runtime performance when not tracing).  The second is
+used to turn the mcount call site into a call to an arbitrary location (but
+typically that is ftracer_caller()).  See the general function definition in
+linux/ftrace.h for the functions:
+        ftrace_make_nop()
+        ftrace_make_call()
+The rec->ip value is the address of the mcount call site that was collected
+by the scripts/recordmcount.pl during build time.
+
+The last function is used to do runtime patching of the active tracer.  This
+will be modifying the assembly code at the location of the ftrace_call symbol
+inside of the ftrace_caller() function.  So you should have sufficient padding
+at that location to support the new function calls you'll be inserting.  Some
+people will be using a "call" type instruction while others will be using a
+"branch" type instruction.  Specifically, the function is:
+        ftrace_update_ftrace_func()
+
+
+HAVE_DYNAMIC_FTRACE + HAVE_FUNCTION_GRAPH_TRACER
+------------------------------------------------
+
+The function grapher needs a few tweaks in order to work with dynamic ftrace.
+Basically, you will need to:
+        - update:
+                - ftrace_caller()
+                - ftrace_graph_call()
+                - ftrace_graph_caller()
+        - implement:
+                - ftrace_enable_ftrace_graph_caller()
+                - ftrace_disable_ftrace_graph_caller()
 
 <details to be filled>
+Quick notes:
+        - add a nop stub after the ftrace_call location named ftrace_graph_call;
+          stub needs to be large enough to support a call to ftrace_graph_caller()
+        - update ftrace_graph_caller() to work with being called by the new
+          ftrace_caller() since some semantics may have changed
+        - ftrace_enable_ftrace_graph_caller() will runtime patch the
+          ftrace_graph_call location with a call to ftrace_graph_caller()
+        - ftrace_disable_ftrace_graph_caller() will runtime patch the
+          ftrace_graph_call location with nops
diff --git a/Documentation/trace/kmemtrace.txt b/Documentation/trace/kmemtrace.txt
deleted file mode 100644
index 6308735e58ca..000000000000
--- a/Documentation/trace/kmemtrace.txt
+++ /dev/null
@@ -1,126 +0,0 @@
-                        kmemtrace - Kernel Memory Tracer
-
-                          by Eduard - Gabriel Munteanu
-                             <eduard.munteanu@linux360.ro>
-
-I. Introduction
-===============
-
-kmemtrace helps kernel developers figure out two things:
-1) how different allocators (SLAB, SLUB etc.) perform
-2) how kernel code allocates memory and how much
-
-To do this, we trace every allocation and export information to the userspace
-through the relay interface. We export things such as the number of requested
-bytes, the number of bytes actually allocated (i.e. including internal
-fragmentation), whether this is a slab allocation or a plain kmalloc() and so
-on.
-
-The actual analysis is performed by a userspace tool (see section III for
-details on where to get it from). It logs the data exported by the kernel,
-processes it and (as of writing this) can provide the following information:
-- the total amount of memory allocated and fragmentation per call-site
-- the amount of memory allocated and fragmentation per allocation
-- total memory allocated and fragmentation in the collected dataset
-- number of cross-CPU allocation and frees (makes sense in NUMA environments)
-
-Moreover, it can potentially find inconsistent and erroneous behavior in
-kernel code, such as using slab free functions on kmalloc'ed memory or
-allocating less memory than requested (but not truly failed allocations).
-
-kmemtrace also makes provisions for tracing on some arch and analysing the
-data on another.
-
-II. Design and goals
-====================
-
-kmemtrace was designed to handle rather large amounts of data. Thus, it uses
-the relay interface to export whatever is logged to userspace, which then
-stores it. Analysis and reporting is done asynchronously, that is, after the
-data is collected and stored. By design, it allows one to log and analyse
-on different machines and different arches.
-
-As of writing this, the ABI is not considered stable, though it might not
-change much. However, no guarantees are made about compatibility yet. When
-deemed stable, the ABI should still allow easy extension while maintaining
-backward compatibility. This is described further in Documentation/ABI.
-
-Summary of design goals:
-        - allow logging and analysis to be done across different machines
-        - be fast and anticipate usage in high-load environments (*)
-        - be reasonably extensible
-        - make it possible for GNU/Linux distributions to have kmemtrace
-        included in their repositories
-
-(*) - one of the reasons Pekka Enberg's original userspace data analysis
-    tool's code was rewritten from Perl to C (although this is more than a
-    simple conversion)
-
-
-III. Quick usage guide
-======================
-
-1) Get a kernel that supports kmemtrace and build it accordingly (i.e. enable
-CONFIG_KMEMTRACE).
-
-2) Get the userspace tool and build it:
-$ git clone git://repo.or.cz/kmemtrace-user.git         # current repository
-$ cd kmemtrace-user/
-$ ./autogen.sh
-$ ./configure
-$ make
-
-3) Boot the kmemtrace-enabled kernel if you haven't, preferably in the
-'single' runlevel (so that relay buffers don't fill up easily), and run
-kmemtrace:
-# '$' does not mean user, but root here.
-$ mount -t debugfs none /sys/kernel/debug
-$ mount -t proc none /proc
-$ cd path/to/kmemtrace-user/
-$ ./kmemtraced
-Wait a bit, then stop it with CTRL+C.
-$ cat /sys/kernel/debug/kmemtrace/total_overruns        # Check if we didn't
-                                                        # overrun, should
-                                                        # be zero.
-$ (Optionally) [Run kmemtrace_check separately on each cpu[0-9]*.out file to
-                check its correctness]
-$ ./kmemtrace-report
-
-Now you should have a nice and short summary of how the allocator performs.
-
-IV. FAQ and known issues
-========================
-
-Q: 'cat /sys/kernel/debug/kmemtrace/total_overruns' is non-zero, how do I fix
-this? Should I worry?
-A: If it's non-zero, this affects kmemtrace's accuracy, depending on how
-large the number is. You can fix it by supplying a higher
-'kmemtrace.subbufs=N' kernel parameter.
----
-
-Q: kmemtrace_check reports errors, how do I fix this? Should I worry?
-A: This is a bug and should be reported. It can occur for a variety of
-reasons:
-        - possible bugs in relay code
-        - possible misuse of relay by kmemtrace
-        - timestamps being collected unorderly
-Or you may fix it yourself and send us a patch.
----
-
-Q: kmemtrace_report shows many errors, how do I fix this? Should I worry?
-A: This is a known issue and I'm working on it. These might be true errors
-in kernel code, which may have inconsistent behavior (e.g. allocating memory
-with kmem_cache_alloc() and freeing it with kfree()). Pekka Enberg pointed
-out this behavior may work with SLAB, but may fail with other allocators.
-
-It may also be due to lack of tracing in some unusual allocator functions.
-
-We don't want bug reports regarding this issue yet.
----
-
-V. See also
-===========
-
-Documentation/kernel-parameters.txt
-Documentation/ABI/testing/debugfs-kmemtrace
-
diff --git a/Documentation/trace/kprobetrace.txt b/Documentation/trace/kprobetrace.txt
index ec94748ae65b..5f77d94598dd 100644
--- a/Documentation/trace/kprobetrace.txt
+++ b/Documentation/trace/kprobetrace.txt
@@ -42,7 +42,7 @@ Synopsis of kprobe_events
   +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**)
   NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
   FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
-                  (u8/u16/u32/u64/s8/s16/s32/s64) are supported.
+                  (u8/u16/u32/u64/s8/s16/s32/s64) and string are supported.
 
   (*) only for return probe.
   (**) this is useful for fetching a field of data structures.