Messages in this thread Patch in this message | | | From | Josh Poimboeuf <> | Subject | [PATCH v3 2/4] objtool: Add support for C jump tables | Date | Wed, 26 Jun 2019 19:33:53 -0500 |
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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 a standard: objtool will automatically recognize any static local jump table named "jump_table".
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- tools/objtool/check.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 172f99195726..8341c2fff14f 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -18,6 +18,8 @@ #define FAKE_JUMP_OFFSET -1 +#define JUMP_TABLE_SYM_PREFIX "jump_table." + struct alternative { struct list_head list; struct instruction *insn; @@ -997,6 +999,7 @@ static struct rela *find_switch_table(struct objtool_file *file, struct instruction *orig_insn = insn; struct section *rodata_sec; unsigned long table_offset; + struct symbol *sym; /* * Backward search using the @first_jump_src links, these help avoid @@ -1035,9 +1038,18 @@ 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. Each jump table should be a static + * local const array named "jump_table" for objtool to + * recognize it. Note: GCC will add a numbered suffix to the + * ELF symbol name, like "jump_table.12345", which it does for + * all static local variables. */ - if (find_symbol_containing(rodata_sec, table_offset)) + sym = find_symbol_containing(rodata_sec, table_offset); + if (sym && strncmp(sym->name, JUMP_TABLE_SYM_PREFIX, + strlen(JUMP_TABLE_SYM_PREFIX))) continue; rodata_rela = find_rela_by_dest(rodata_sec, table_offset); -- 2.20.1
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