powerpc/ftrace: Ignore weak functions

Extend commit b39181f7c6907d ("ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to
avoid adding weak function") to ppc32 and ppc64 -mprofile-kernel by
defining FTRACE_MCOUNT_MAX_OFFSET.

For ppc64 -mprofile-kernel ABI, we can have two instructions at function
entry for TOC setup followed by 'mflr r0' and 'bl _mcount'. So, the
mcount location is at most the 4th instruction in a function. For ppc32,
mcount location is always the 3rd instruction in a function, preceded by
'mflr r0' and 'stw r0,4(r1)'.

With this patch, and with ppc64le_guest_defconfig and some ftrace/bpf
config items enabled:
# grep __ftrace_invalid_address available_filter_functions | wc -l
79

Signed-off-by: Naveen N. Rao <[e-mail]>
Acked-by: Steven Rostedt (Google) <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/include/asm/ftrace.h

···
 
 #define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 
+/* Ignore unused weak functions which will have larger offsets */
+#ifdef CONFIG_MPROFILE_KERNEL
+#define FTRACE_MCOUNT_MAX_OFFSET	12
+#elif defined(CONFIG_PPC32)
+#define FTRACE_MCOUNT_MAX_OFFSET	8
+#endif
+
 #ifndef __ASSEMBLY__
 extern void _mcount(void);