Messages in this thread Patch in this message | | | Subject | Re: [PATCH V3 3/9] objtool: Add support for intra-function calls | From | Julien Thierry <> | Date | Tue, 14 Apr 2020 13:07:34 +0100 |
| |
Hi Alexandre,
On 4/14/20 11:36 AM, Alexandre Chartre wrote: > Change objtool to support intra-function calls. On x86, an intra-function > call is represented in objtool as a push onto the stack (of the return > 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> > --- > include/linux/frame.h | 11 ++ > .../Documentation/stack-validation.txt | 8 ++ > tools/objtool/arch/x86/decode.c | 6 + > tools/objtool/check.c | 126 ++++++++++++++---- > tools/objtool/check.h | 1 + > 5 files changed, 128 insertions(+), 24 deletions(-) > > diff --git a/include/linux/frame.h b/include/linux/frame.h > index 02d3ca2d9598..c7178e6c9d48 100644 > --- a/include/linux/frame.h > +++ b/include/linux/frame.h > @@ -15,9 +15,20 @@ > static void __used __section(.discard.func_stack_frame_non_standard) \ > *__func_stack_frame_non_standard_##func = func > > +/* > + * This macro indicates that the following intra-function call is valid. > + * Any non-annotated intra-function call will cause objtool to issue warning. > + */ > +#define ANNOTATE_INTRA_FUNCTION_CALL \ > + 999: \ > + .pushsection .discard.intra_function_call; \
Very nit-pickish but my brain wants to add an 's' to that section name. Like for the sections "unwind_hints" or "altinstructions".
> + .long 999b; \ > + .popsection; > + > #else /* !CONFIG_STACK_VALIDATION */ > > #define STACK_FRAME_NON_STANDARD(func) > +#define ANNOTATE_INTRA_FUNCTION_CALL > > #endif /* CONFIG_STACK_VALIDATION */ > > diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt > index de094670050b..09f863fd32d2 100644 > --- a/tools/objtool/Documentation/stack-validation.txt > +++ b/tools/objtool/Documentation/stack-validation.txt > @@ -290,6 +290,14 @@ they mean, and suggestions for how to fix them. > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 > > > +9. file.o: warning: unsupported intra-function call > + > + This warning means that a direct call is done to a destination which > + is not at the beginning of a function. If this is a legit call, you > + can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL > + directive right before the call. > + > + > If the error doesn't seem to make sense, it could be a bug in objtool. > Feel free to ask the objtool maintainer for help. > > diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c > index a62e032863a8..f4d70b8835c4 100644 > --- a/tools/objtool/arch/x86/decode.c > +++ b/tools/objtool/arch/x86/decode.c > @@ -437,6 +437,12 @@ int arch_decode_instruction(struct elf *elf, struct section *sec, > > case 0xe8: > *type = INSN_CALL; > + /* > + * For the impact on the stack, a call behaves like > + * a push of an immediate value (the return address). > + */ > + op->src.type = OP_SRC_CONST; > + op->dest.type = OP_DEST_PUSH; > break; > > case 0xfc: > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > index 8f0525d5d895..ad362c5de281 100644 > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -654,44 +654,58 @@ static int add_jump_destinations(struct objtool_file *file) > return 0; > } > > +static int configure_call(struct objtool_file *file, struct instruction *insn)
The name "configure_call()" is a bit vague. What about naming this set_local_call_destination() ? (Since it deals with call destinations that don't need relocations and sets their actual target destination).
> +{ > + unsigned long dest_off; > + > + dest_off = insn->offset + insn->len + insn->immediate; > + insn->call_dest = find_func_by_offset(insn->sec, dest_off); > + if (!insn->call_dest) > + insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); > + > + if (insn->call_dest) { > + /* regular call */ > + if (insn->func && insn->call_dest->type != STT_FUNC) { > + WARN_FUNC("unsupported call to non-function", > + insn->sec, insn->offset); > + return -1; > + } > + return 0; > + } > + > + /* intra-function call */ > + if (!insn->intra_function_call) > + WARN_FUNC("intra-function call", insn->sec, insn->offset); > + > + dest_off = insn->offset + insn->len + insn->immediate; > + insn->jump_dest = find_insn(file, insn->sec, dest_off); > + if (!insn->jump_dest) { > + WARN_FUNC("can't find call dest at %s+0x%lx", > + insn->sec, insn->offset, > + insn->sec->name, dest_off); > + return -1; > + } > + > + return 0; > +} > + > /* > * Find the destination instructions for all calls. > */ > static int add_call_destinations(struct objtool_file *file) > { > struct instruction *insn; > - unsigned long dest_off; > struct rela *rela; > > for_each_insn(file, insn) { > - if (insn->type != INSN_CALL) > + if (insn->type != INSN_CALL || insn->ignore) > continue; > > rela = find_rela_by_dest_range(file->elf, insn->sec, > insn->offset, insn->len); > if (!rela) { > - dest_off = insn->offset + insn->len + insn->immediate; > - insn->call_dest = find_func_by_offset(insn->sec, dest_off); > - if (!insn->call_dest) > - insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); > - > - if (insn->ignore) > - continue; > - > - if (!insn->call_dest) { > - WARN_FUNC("unsupported intra-function call", > - insn->sec, insn->offset); > - if (retpoline) > - WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE."); > - return -1; > - } > - > - if (insn->func && insn->call_dest->type != STT_FUNC) { > - WARN_FUNC("unsupported call to non-function", > - insn->sec, insn->offset); > + if (configure_call(file, insn)) > return -1; > - } > - > } else if (rela->sym->type == STT_SECTION) { > insn->call_dest = find_func_by_offset(rela->sym->sec, > rela->addend+4); > @@ -1337,6 +1351,42 @@ 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"); > + 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 direct call", > + insn->sec, insn->offset); > + return -1; > + } > + > + insn->intra_function_call = true;
Maybe you could directly lookup the target instruction here and set insn->jump_dest here.
Then you wouldn't need as much changes in add_call_destination(), just adding the following in the "!rela" branch:
if (insn->intra_function_call) continue;
> + } > + > + return 0; > +} > + > static void mark_rodata(struct objtool_file *file) > { > struct section *sec; > @@ -1392,6 +1442,10 @@ 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; > @@ -2155,7 +2209,8 @@ 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; > @@ -2164,6 +2219,29 @@ 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) { > + /* > + * The call instruction can update the stack > + * state. Then make the intra-function call > + * behaves like and unconditional jump. > + */ > + ret = update_insn_state(insn, &state); > + if (ret) > + return ret; > + > + ret = validate_branch(file, func, insn, > + insn->jump_dest, state); > + if (ret) { > + if (backtrace) { > + BT_FUNC("(intra-function call)", > + insn); > + } > + return ret; > + } > + > + return 0; > + } > + > break; > > case INSN_JUMP_CONDITIONAL: > diff --git a/tools/objtool/check.h b/tools/objtool/check.h > index 953db38dfc35..6a80903fc4aa 100644 > --- a/tools/objtool/check.h > +++ b/tools/objtool/check.h > @@ -36,6 +36,7 @@ struct instruction { > int alt_group; > bool dead_end, ignore, ignore_alts; > bool hint, save, restore; > + bool intra_function_call; > bool retpoline_safe; > u8 visited; > struct symbol *call_dest; >
Cheers,
-- Julien Thierry
| |