ftrace: Match dot symbols when searching functions on ppc64

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 <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 9dac18dabd03c5a5f2135aee190a463212393fee..1123a4d8d8dd60411c99342b607d9cda26e4be15 100644 (file)
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -607,3 +607,13 @@ unsigned long __init arch_syscall_addr(int nr)
        return sys_call_table[nr*2];
 }
 #endif /* CONFIG_FTRACE_SYSCALLS && CONFIG_PPC64 */
+
+#if defined(CONFIG_PPC64) && (!defined(_CALL_ELF) || _CALL_ELF != 2)
+char *arch_ftrace_match_adjust(char *str, const char *search)
+{
+       if (str[0] == '.' && search[0] != '.')
+               return str + 1;
+       else
+               return str;
+}
+#endif /* defined(CONFIG_PPC64) && (!defined(_CALL_ELF) || _CALL_ELF != 2) */

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7e8d792da9630ee9db915e7e849de268ff999878..a6c8252d7776b3954df1db09fb1831c603093c7c 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3456,11 +3456,23 @@ struct ftrace_glob {
        int type;
 };
 
+/*
+ * If symbols in an architecture don't correspond exactly to the user-visible
+ * name of what they represent, it is possible to define this function to
+ * perform the necessary adjustments.
+*/
+char * __weak arch_ftrace_match_adjust(char *str, const char *search)
+{
+       return str;
+}
+
 static int ftrace_match(char *str, struct ftrace_glob *g)
 {
        int matched = 0;
        int slen;
 
+       str = arch_ftrace_match_adjust(str, g->search);
+
        switch (g->type) {
        case MATCH_FULL:
                if (strcmp(str, g->search) == 0)