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authorJosh Poimboeuf <jpoimboe@redhat.com>2019-06-27 20:50:46 -0500
committerIngo Molnar <mingo@kernel.org>2019-07-09 13:55:46 +0200
commit87b512def792579641499d9bef1d640994ea9c18 (patch)
treebac6ea7c9a3a0822b358931ff7260eecfb9a1f59 /tools
parent222a21d29521d144f3dd7a0bc4d4020e448f0126 (diff)
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objtool: Add support for C jump tables
Objtool doesn't know how to read C jump tables, so it has to whitelist functions which use them, causing missing ORC unwinder data for such functions, e.g. ___bpf_prog_run(). C jump tables are very similar to GCC switch jump tables, which objtool already knows how to read. So adding support for C jump tables is easy. It just needs to be able to find the tables and distinguish them from other data. To allow the jump tables to be found, create an __annotate_jump_table macro which can be used to annotate them. The annotation is done by placing the jump table in an .rodata..c_jump_table section. The '.rodata' prefix ensures that the data will be placed in the rodata section by the vmlinux linker script. The double periods are part of an existing convention which distinguishes kernel sections from GCC sections. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Song Liu <songliubraving@fb.com> Cc: Kairui Song <kasong@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Link: https://lkml.kernel.org/r/0ba2ca30442b16b97165992381ce643dc27b3d1a.1561685471.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'tools')
-rw-r--r--tools/objtool/check.c27
1 files changed, 20 insertions, 7 deletions
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;
}