Impact: avoid section mismatch warning, clean up
The dynamic ftrace determines which nop is safe to use at start up.
When it finds a safe nop for patching, it sets a pointer called ftrace_nop
to point to the code. All call sites are then patched to this nop.
Later, when tracing is turned on, this ftrace_nop variable is again used
to compare the location to make sure it is a nop before we update it to
an mcount call. If this fails just once, a warning is printed and ftrace
is disabled.
Rakib Mullick noted that the code that sets up the nop is a .init section
where as the nop itself is in the .text section. This is needed because
the nop is used later on after boot up. The problem is that the test of the
nop jumps back to the setup code and causes a "section mismatch" warning.
Rakib first recommended to convert the nop to .init.text, but as stated
above, this would fail since that text is used later.
The real solution is to extend Rabik's patch, and to make the ftrace_nop
into an array, and just save the code from the assembly to this array.
Now the section can stay as an init section, and we have a nop to use
later on.
Reported-by: Rakib Mullick <rakib.mullick@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
-/* Long is fine, even if it is only 4 bytes ;-) */
-static unsigned long *ftrace_nop;
+static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];
union ftrace_code_union {
char code[MCOUNT_INSN_SIZE];
union ftrace_code_union {
char code[MCOUNT_INSN_SIZE];
unsigned char *ftrace_nop_replace(void)
{
unsigned char *ftrace_nop_replace(void)
{
- return (char *)ftrace_nop;
}
unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
}
unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
* TODO: check the cpuid to determine the best nop.
*/
asm volatile (
* TODO: check the cpuid to determine the best nop.
*/
asm volatile (
- "jmp ftrace_test_jmp\n"
- /* This code needs to stay around */
- ".section .text, \"ax\"\n"
"ftrace_test_jmp:"
"jmp ftrace_test_p6nop\n"
"nop\n"
"ftrace_test_jmp:"
"jmp ftrace_test_p6nop\n"
"nop\n"
"jmp 1f\n"
"ftrace_test_nop5:"
".byte 0x66,0x66,0x66,0x66,0x90\n"
"jmp 1f\n"
"ftrace_test_nop5:"
".byte 0x66,0x66,0x66,0x66,0x90\n"
- "jmp 1f\n"
- ".previous\n"
"1:"
".section .fixup, \"ax\"\n"
"2: movl $1, %0\n"
"1:"
".section .fixup, \"ax\"\n"
"2: movl $1, %0\n"
switch (faulted) {
case 0:
pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
switch (faulted) {
case 0:
pr_info("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
- ftrace_nop = (unsigned long *)ftrace_test_p6nop;
+ memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE);
break;
case 1:
pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
break;
case 1:
pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
- ftrace_nop = (unsigned long *)ftrace_test_nop5;
+ memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE);
break;
case 2:
pr_info("ftrace: converting mcount calls to jmp . + 5\n");
break;
case 2:
pr_info("ftrace: converting mcount calls to jmp . + 5\n");
- ftrace_nop = (unsigned long *)ftrace_test_jmp;
+ memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE);