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authorIlya Leoshkevich <iii@linux.ibm.com>2021-07-29 00:25:45 +0300
committerHeiko Carstens <hca@linux.ibm.com>2021-08-03 15:31:40 +0300
commit67ccddf86621b18dbffe56f11a106774ee8f44bd (patch)
treecbc130b1c3c4da92e7c87b8cd5c70942e697ab60 /include/linux/ftrace.h
parentd80d3ea64e5fa2ab20b3774ea0d871484877422b (diff)
downloadlinux-67ccddf86621b18dbffe56f11a106774ee8f44bd.tar.xz
ftrace: Introduce ftrace_need_init_nop()
Implementing live patching on s390 requires each function's prologue to contain a very special kind of nop, which gcc and clang don't generate. However, the current code assumes that if CC_USING_NOP_MCOUNT is defined, then whatever the compiler generates is good enough. Move the CC_USING_NOP_MCOUNT check into the new ftrace_need_init_nop() macro, that the architectures can override. An alternative solution is to disable using -mnop-mcount in the Makefile, however, this makes the build logic (even) more complicated and forces the arch-specific code to deal with the useless __fentry__ symbol. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Link: https://lore.kernel.org/r/20210728212546.128248-2-iii@linux.ibm.com Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Diffstat (limited to 'include/linux/ftrace.h')
-rw-r--r--include/linux/ftrace.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a69f363b61bf..832e65f06754 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -643,6 +643,22 @@ static inline int ftrace_disable_ftrace_graph_caller(void) { return 0; }
extern int ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr);
+/**
+ * ftrace_need_init_nop - return whether nop call sites should be initialized
+ *
+ * Normally the compiler's -mnop-mcount generates suitable nops, so we don't
+ * need to call ftrace_init_nop() if the code is built with that flag.
+ * Architectures where this is not always the case may define their own
+ * condition.
+ *
+ * Return must be:
+ * 0 if ftrace_init_nop() should be called
+ * Nonzero if ftrace_init_nop() should not be called
+ */
+
+#ifndef ftrace_need_init_nop
+#define ftrace_need_init_nop() (!__is_defined(CC_USING_NOP_MCOUNT))
+#endif
/**
* ftrace_init_nop - initialize a nop call site