Messages in this thread | | | Subject | Re: [PATCH 3/7] objtool: Add support for intra-function calls | From | Alexandre Chartre <> | Date | Thu, 2 Apr 2020 15:24:45 +0200 |
| |
On 4/2/20 2:53 PM, Julien Thierry wrote: > Hi Alexandre, > > I ran into the limitation of intra-function call for the arm64 > support but didn't take the time to make a clean patch to support > them properly. > > Nice to see you've gone through that work :) . > > On 4/2/20 9:22 AM, Alexandre Chartre wrote: >> Change objtool to support intra-function calls. An intra-function call >> is represented in objtool as a push onto the stack (of the return > > I have to disagree a bit with that. The push onto the stack is true > on x86, but other architectures might not have that (arm/arm64 have a > link register that gets set by "bl" instructions and do not modify > the stack).
Correct, this is x86 specific.
> >> address), and a jump to the destination address. That way the stack >> information is correctly updated and the call flow is still accurate. >> >> Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> >> --- >> tools/objtool/check.c | 73 ++++++++++++++++++++++++++++++++++++++++++- >> tools/objtool/check.h | 1 + >> 2 files changed, 73 insertions(+), 1 deletion(-) >> >> diff --git a/tools/objtool/check.c b/tools/objtool/check.c >> index 214809ac2776..0cec91291d46 100644 >> --- a/tools/objtool/check.c >> +++ b/tools/objtool/check.c >> @@ -657,6 +657,18 @@ static int add_call_destinations(struct objtool_file *file) >> if (insn->type != INSN_CALL) >> continue; >> + if (insn->intra_function_call) { >> + dest_off = insn->offset + insn->len + insn->immediate; >> + insn->jump_dest = find_insn(file, insn->sec, dest_off); >> + if (insn->jump_dest) >> + continue; >> + >> + WARN_FUNC("can't find call dest at %s+0x%lx", >> + insn->sec, insn->offset, >> + insn->sec->name, dest_off); >> + return -1; >> + } >> + >> rela = find_rela_by_dest_range(insn->sec, insn->offset, >> insn->len); >> if (!rela) { >> @@ -1289,6 +1301,49 @@ static int read_retpoline_hints(struct objtool_file *file) >> return 0; >> } >> +static int read_intra_function_call(struct objtool_file *file) >> +{ >> + struct section *sec; >> + struct instruction *insn; >> + struct rela *rela; >> + >> + sec = find_section_by_name(file->elf, >> + ".rela.discard.intra_function_call"); > > I'm wondering, do we really need to annotate the intra_function_call > and group the in a section? > > Would it be a problem to consider all (static) call instructions with > a destination that is not the start offset of a symbol to be an > intra-function call (and set insn->intra_function_call and > insn->jump_dest accordingly)?
Correct, we could automatically detect intra-function calls instead of having to annotate them. However, I choose to annotate them because I don't think that's not an expected construct in a "normal" code flow (at least on x86). So objtool would still issue a warning on intra-function calls by default, and you can annotate them to indicate if they are expected.
If intra-function calls are frequent on arm then I can add an option to objtool so it automatically detects them. This way, we won't use the option on x86 and we have to annotate intra-function call on x86, and you can use it on arm to automatically detect intra-function calls.
> Other than that the logic would stay the same. > >> + if (!sec) >> + return 0; >> + >> + list_for_each_entry(rela, &sec->rela_list, list) { >> + if (rela->sym->type != STT_SECTION) { >> + WARN("unexpected relocation symbol type in %s", >> + sec->name); >> + return -1; >> + } >> + >> + insn = find_insn(file, rela->sym->sec, rela->addend); >> + if (!insn) { >> + WARN("bad .discard.intra_function_call entry"); >> + return -1; >> + } >> + >> + if (insn->type != INSN_CALL) { >> + WARN_FUNC("intra_function_call not a call", >> + insn->sec, insn->offset); > > Nit: This could be slightly confusing with INSN_CALL_DYNAMIC. Maybe just: > "unsupported instruction for intra-function call " ?
Right, I will change that: "intra_function_call not a direct call"
>> + return -1; >> + } >> + >> + insn->intra_function_call = true; >> + /* >> + * For the impact on the stack, make an intra-function >> + * call behaves like a push of an immediate value (the >> + * return address). >> + */ >> + insn->stack_op.src.type = OP_SRC_CONST; >> + insn->stack_op.dest.type = OP_DEST_PUSH; > > As commented above, this should be arch dependent.
I will add a arch dependent call. I will also do that for the return trampoline call case (patch 4).
Thanks,
alex.
>> + } >> + >> + return 0; >> +} >> + >> static void mark_rodata(struct objtool_file *file) >> { >> struct section *sec; >> @@ -1344,6 +1399,10 @@ static int decode_sections(struct objtool_file *file) >> if (ret) >> return ret; >> + ret = read_intra_function_call(file); >> + if (ret) >> + return ret; >> + >> ret = add_call_destinations(file); >> if (ret) >> return ret; >> @@ -2092,7 +2151,8 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, >> return ret; >> if (!no_fp && func && !is_fentry_call(insn) && >> - !has_valid_stack_frame(&state)) { >> + !has_valid_stack_frame(&state) && >> + !insn->intra_function_call) { >> WARN_FUNC("call without frame pointer save/setup", >> sec, insn->offset); >> return 1; >> @@ -2101,6 +2161,17 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, >> if (dead_end_function(file, insn->call_dest)) >> return 0; >> + if (insn->intra_function_call) { >> + update_insn_state(insn, &state); >> + ret = validate_branch(file, func, insn, >> + insn->jump_dest, state); >> + if (ret) { >> + if (backtrace) >> + BT_FUNC("(intra-call)", insn); >> + return ret; >> + } >> + } >> + >> break; >> case INSN_JUMP_CONDITIONAL: >> diff --git a/tools/objtool/check.h b/tools/objtool/check.h >> index cffb23d81782..2bd6d2f46baa 100644 >> --- a/tools/objtool/check.h >> +++ b/tools/objtool/check.h >> @@ -35,6 +35,7 @@ struct instruction { >> unsigned long immediate; >> unsigned int alt_group; >> bool dead_end, ignore, hint, save, restore, ignore_alts; >> + bool intra_function_call; >> bool retpoline_safe; >> u8 visited; >> struct symbol *call_dest; >> > > Thanks, >
| |