Messages in this thread Patch in this message | | | From | Josh Poimboeuf <> | Subject | [PATCH 1/2] objtool: Fix clang switch table edge case | Date | Mon, 17 Feb 2020 21:41:53 -0600 |
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Clang has the ability to create a switch table which is not a jump table, but is rather a table of string pointers. This confuses objtool, because it sees the relocations for the string pointers and assumes they're part of a jump table:
drivers/ata/sata_dwc_460ex.o: warning: objtool: sata_dwc_bmdma_start_by_tag()+0x3a2: can't find switch jump table net/ceph/messenger.o: warning: objtool: ceph_con_workfn()+0x47c: can't find switch jump table
Make objtool's find_jump_table() smart enough to distinguish between a switch jump table (which has relocations to text addresses in the same function as the original instruction) and other anonymous rodata (which may have relocations to elsewhere).
Link: https://github.com/ClangBuiltLinux/linux/issues/485 Reported-by: Nick Desaulniers <ndesaulniers@google.com> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> --- tools/objtool/check.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index b6da413bcbd6..e7227649bac7 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1019,7 +1019,7 @@ static struct rela *find_jump_table(struct objtool_file *file, struct instruction *insn) { struct rela *text_rela, *table_rela; - struct instruction *orig_insn = insn; + struct instruction *dest_insn, *orig_insn = insn; struct section *table_sec; unsigned long table_offset; @@ -1071,10 +1071,17 @@ static struct rela *find_jump_table(struct objtool_file *file, strcmp(table_sec->name, C_JUMP_TABLE_SECTION)) continue; - /* Each table entry has a rela associated with it. */ + /* + * Each table entry has a rela associated with it. The rela + * should reference text in the same function as the original + * instruction. + */ table_rela = find_rela_by_dest(table_sec, table_offset); if (!table_rela) continue; + dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend); + if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func) + continue; /* * Use of RIP-relative switch jumps is quite rare, and -- 2.21.1
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