ftrace: enable mcount recording for modules

This patch enables the loading of the __mcount_section of modules and
changing all the callers of mcount into nops.

The modification is done before the init_module function is called, so
again, we do not need to use kstop_machine to make these changes.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 19 insertions, 0 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index d4d6ab453b78..4936489f9ed8 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -164,8 +164,11 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3) { }
 
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 extern void ftrace_init(void);
+extern void ftrace_init_module(unsigned long *start, unsigned long *end);
 #else
 static inline void ftrace_init(void) { }
+static inline void
+ftrace_init_module(unsigned long *start, unsigned long *end) { }
 #endif
 
 #endif /* _LINUX_FTRACE_H */
diff --git a/kernel/module.c b/kernel/module.c
index 661d73db786e..d753fd9d83ec 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -47,6 +47,7 @@
 #include <linux/license.h>
 #include <asm/sections.h>
 #include <linux/tracepoint.h>
+#include <linux/ftrace.h>
 
 #if 0
 #define DEBUGP printk
@@ -1834,6 +1835,7 @@ static noinline struct module *load_module(void __user *umod,
         unsigned int markersstringsindex;
         unsigned int tracepointsindex;
         unsigned int tracepointsstringsindex;
+        unsigned int mcountindex;
         struct module *mod;
         long err = 0;
         void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -2124,6 +2126,9 @@ static noinline struct module *load_module(void __user *umod,
         tracepointsstringsindex = find_sec(hdr, sechdrs, secstrings,
                                         "__tracepoints_strings");
 
+        mcountindex = find_sec(hdr, sechdrs, secstrings,
+                               "__mcount_loc");
+
         /* Now do relocations. */
         for (i = 1; i < hdr->e_shnum; i++) {
                 const char *strtab = (char *)sechdrs[strindex].sh_addr;
@@ -2184,6 +2189,12 @@ static noinline struct module *load_module(void __user *umod,
                         mod->tracepoints + mod->num_tracepoints);
 #endif
         }
+
+        if (mcountindex) {
+                void *mseg = (void *)sechdrs[mcountindex].sh_addr;
+                ftrace_init_module(mseg, mseg + sechdrs[mcountindex].sh_size);
+        }
+
         err = module_finalize(hdr, sechdrs, mod);
         if (err < 0)
                 goto cleanup;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index df96d5990c04..ea45bb1c0fd6 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1541,6 +1541,11 @@ static int ftrace_convert_nops(unsigned long *start,
         return 0;
 }
 
+void ftrace_init_module(unsigned long *start, unsigned long *end)
+{
+        ftrace_convert_nops(start, end);
+}
+
 extern unsigned long __start_mcount_loc[];
 extern unsigned long __stop_mcount_loc[];