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-rw-r--r--include/linux/compiler.h5
-rw-r--r--tools/objtool/check.c27
2 files changed, 25 insertions, 7 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 8aaf7cd026b0..f0fd5636fddb 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -116,9 +116,14 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
".pushsection .discard.unreachable\n\t" \
".long 999b - .\n\t" \
".popsection\n\t"
+
+/* Annotate a C jump table to allow objtool to follow the code flow */
+#define __annotate_jump_table __section(".rodata..c_jump_table")
+
#else
#define annotate_reachable()
#define annotate_unreachable()
+#define __annotate_jump_table
#endif
#ifndef ASM_UNREACHABLE
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 172f99195726..27818a93f0b1 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -18,6 +18,8 @@
#define FAKE_JUMP_OFFSET -1
+#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
+
struct alternative {
struct list_head list;
struct instruction *insn;
@@ -1035,9 +1037,15 @@ static struct rela *find_switch_table(struct objtool_file *file,
/*
* Make sure the .rodata address isn't associated with a
- * symbol. gcc jump tables are anonymous data.
+ * symbol. GCC jump tables are anonymous data.
+ *
+ * Also support C jump tables which are in the same format as
+ * switch jump tables. For objtool to recognize them, they
+ * need to be placed in the C_JUMP_TABLE_SECTION section. They
+ * have symbols associated with them.
*/
- if (find_symbol_containing(rodata_sec, table_offset))
+ if (find_symbol_containing(rodata_sec, table_offset) &&
+ strcmp(rodata_sec->name, C_JUMP_TABLE_SECTION))
continue;
rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
@@ -1277,13 +1285,18 @@ static void mark_rodata(struct objtool_file *file)
bool found = false;
/*
- * This searches for the .rodata section or multiple .rodata.func_name
- * sections if -fdata-sections is being used. The .str.1.1 and .str.1.8
- * rodata sections are ignored as they don't contain jump tables.
+ * Search for the following rodata sections, each of which can
+ * potentially contain jump tables:
+ *
+ * - .rodata: can contain GCC switch tables
+ * - .rodata.<func>: same, if -fdata-sections is being used
+ * - .rodata..c_jump_table: contains C annotated jump tables
+ *
+ * .rodata.str1.* sections are ignored; they don't contain jump tables.
*/
for_each_sec(file, sec) {
- if (!strncmp(sec->name, ".rodata", 7) &&
- !strstr(sec->name, ".str1.")) {
+ if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
+ !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
sec->rodata = true;
found = true;
}