From 3b47bfc1fca01cccad9cce2d18b79b18ef2e4131 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 27 Aug 2008 23:24:15 -0400 Subject: [PATCH] ftrace: remove direct reference to mcount in trace code The mcount record method of ftrace scans objdump for references to mcount. Using mcount as the reference to test if the calls to mcount being replaced are indeed calls to mcount, this use of mcount was also caught as a location to change. Using a variable that points to the mcount address moves this reference into the data section that is not scanned, and we do not use a false location to try and modify. The warn on code was what was used to detect this bug. Signed-off-by: Steven Rostedt Signed-off-by: Ingo Molnar --- kernel/trace/ftrace.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 969a83f75a3..b69966f0f14 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -36,6 +36,14 @@ int ftrace_enabled __read_mostly; static int last_ftrace_enabled; +/* + * Since MCOUNT_ADDR may point to mcount itself, we do not want + * to get it confused by reading a reference in the code as we + * are parsing on objcopy output of text. Use a variable for + * it instead. + */ +static unsigned long mcount_addr = MCOUNT_ADDR; + /* * ftrace_disabled is set when an anomaly is discovered. * ftrace_disabled is much stronger than ftrace_enabled. @@ -577,7 +585,7 @@ ftrace_code_disable(struct dyn_ftrace *rec) ip = rec->ip; nop = ftrace_nop_replace(); - call = ftrace_call_replace(ip, MCOUNT_ADDR); + call = ftrace_call_replace(ip, mcount_addr); failed = ftrace_modify_code(ip, call, nop); if (failed) { -- 2.41.1