diff options
| author | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2019-05-09 15:32:05 -0400 |
|---|---|---|
| committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2019-05-10 12:33:09 -0400 |
| commit | 562e14f72292249e52e6346a9e3a30be652b0cf6 (patch) | |
| tree | 25e276f9e975255e922f28d659aebe6de67d8497 /arch/x86/include | |
| parent | 518049d9d3e25dcd7be6e3d728e86f292ad0c922 (diff) | |
ftrace/x86: Remove mcount support
There's two methods of enabling function tracing in Linux on x86. One is
with just "gcc -pg" and the other is "gcc -pg -mfentry". The former will use
calls to a special function "mcount" after the frame is set up in all C
functions. The latter will add calls to a special function called "fentry"
as the very first instruction of all C functions.
At compile time, there is a check to see if gcc supports, -mfentry, and if
it does, it will use that, because it is more versatile and less error prone
for function tracing.
Starting with v4.19, the minimum gcc supported to build the Linux kernel,
was raised to version 4.6. That also happens to be the first gcc version to
support -mfentry. Since on x86, using gcc versions from 4.6 and beyond will
unconditionally enable the -mfentry, it will no longer use mcount as the
method for inserting calls into the C functions of the kernel. This means
that there is no point in continuing to maintain mcount in x86.
Remove support for using mcount. This makes the code less complex, and will
also allow it to be simplified in the future.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'arch/x86/include')
| -rw-r--r-- | arch/x86/include/asm/ftrace.h | 8 | ||||
| -rw-r--r-- | arch/x86/include/asm/livepatch.h | 3 |
2 files changed, 3 insertions, 8 deletions
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h index cf350639e76d..287f1f7b2e52 100644 --- a/arch/x86/include/asm/ftrace.h +++ b/arch/x86/include/asm/ftrace.h @@ -3,12 +3,10 @@ #define _ASM_X86_FTRACE_H #ifdef CONFIG_FUNCTION_TRACER -#ifdef CC_USING_FENTRY -# define MCOUNT_ADDR ((unsigned long)(__fentry__)) -#else -# define MCOUNT_ADDR ((unsigned long)(mcount)) -# define HAVE_FUNCTION_GRAPH_FP_TEST +#ifndef CC_USING_FENTRY +# error Compiler does not support fentry? #endif +# define MCOUNT_ADDR ((unsigned long)(__fentry__)) #define MCOUNT_INSN_SIZE 5 /* sizeof mcount call */ #ifdef CONFIG_DYNAMIC_FTRACE diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h index ed80003ce3e2..2f2bdf0662f8 100644 --- a/arch/x86/include/asm/livepatch.h +++ b/arch/x86/include/asm/livepatch.h @@ -26,9 +26,6 @@ static inline int klp_check_compiler_support(void) { -#ifndef CC_USING_FENTRY - return 1; -#endif return 0; } |