Commit 7132e2d6 authored Apr 25, 2016 by Thiago Jung Bauermann Committed by Michael Ellerman Apr 27, 2016

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>

parent 8fe08885

arch/powerpc/kernel/ftrace.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -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) */

kernel/trace/ftrace.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -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)

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