ftrace: modify the scope of sorting mcount at compile

ANBZ: torvalds#434

commit 4ed308c upstream.

First S390 complained that the sorting of the mcount sections at build
time caused the kernel to crash on their architecture. Now PowerPC is
complaining about it too. And also ARM64 appears to be having issues.

It may be necessary to also update the relocation table for the values
in the mcount table. Not only do we have to sort the table, but also
update the relocations that may be applied to the items in the table.

If the system is not relocatable, then it is fine to sort, but if it is,
some architectures may have issues (although x86 does not as it shifts all
addresses the same).

Add a HAVE_BUILDTIME_MCOUNT_SORT that an architecture can set to say it is
safe to do the sorting at build time.

Also update the config to compile in build time sorting in the sorttable
code in scripts/ to depend on CONFIG_BUILDTIME_MCOUNT_SORT.

Fixes: 1cb7e9c ("anolis: scripts: ftrace_init optimization about sorting")
Reported-by: Sachin Sant <[email protected]>
Tested-by: Sachin Sant <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Yinan Liu <[email protected]>
Reviewed-by: Shanpei Chen <[email protected]>

Author: Yinan Liu

arch/arm/Kconfig

@@ -61,6 +61,7 @@ config ARM
 	select HAVE_EBPF_JIT if !CPU_ENDIAN_BE32
 	select HAVE_CONTEXT_TRACKING
 	select HAVE_C_RECORDMCOUNT
+	select HAVE_BUILDTIME_MCOUNT_SORT
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS if MMU
 	select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU

arch/x86/Kconfig

@@ -135,6 +135,7 @@ config X86
 	select HAVE_CONTEXT_TRACKING		if X86_64
 	select HAVE_COPY_THREAD_TLS
 	select HAVE_C_RECORDMCOUNT
+	select HAVE_BUILDTIME_MCOUNT_SORT
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DMA_CONTIGUOUS

kernel/trace/Kconfig

@@ -57,6 +57,19 @@ config HAVE_C_RECORDMCOUNT
 	help
 	  C version of recordmcount available?
 
+config HAVE_BUILDTIME_MCOUNT_SORT
+	bool
+	help
+	  An architecture selects this if it sorts the mcount_loc section
+	  at build time.
+
+config BUILDTIME_MCOUNT_SORT
+	bool
+	default y
+	depends on HAVE_BUILDTIME_MCOUNT_SORT && DYNAMIC_FTRACE
+	help
+	  Sort the mcount_loc section at build time.
+
 config TRACER_MAX_TRACE
 	bool
 

kernel/trace/ftrace.c

@@ -5554,7 +5554,7 @@ static int ftrace_process_locs(struct module *mod,
 	 * CONFIG_BUILDTIME_TABLE_SORT, while mcount loc in
 	 * modules can not be sorted at build time.
 	 */
-	if (!IS_ENABLED(CONFIG_BUILDTIME_TABLE_SORT) || mod) {
+	if (!IS_ENABLED(CONFIG_BUILDTIME_MCOUNT_SORT) || mod) {
 		sort(start, count, sizeof(*start),
 		     ftrace_cmp_ips, NULL);
 	}

scripts/Makefile

@@ -34,7 +34,7 @@ HOSTCFLAGS_sorttable.o += -DUNWINDER_ORC_ENABLED
 endif
 endif
 
-ifdef CONFIG_FUNCTION_TRACER
+ifdef CONFIG_BUILDTIME_MCOUNT_SORT
 HOSTCFLAGS_sorttable.o += -DMCOUNT_SORT_ENABLED
 endif
 

scripts/sorttable.h

@@ -285,7 +285,7 @@ static int do_sort(Elf_Ehdr *ehdr,
 	unsigned int shnum;
 	unsigned int shstrndx;
 #ifdef MCOUNT_SORT_ENABLED
-	struct elf_mcount_loc mstruct;
+	struct elf_mcount_loc mstruct = {0};
 	uint_t _start_mcount_loc = 0;
 	uint_t _stop_mcount_loc = 0;
 	pthread_t mcount_sort_thread = 0;