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[86.202.218.107]) by smtp.gmail.com with ESMTPSA id 9sm6802824wmm.6.2020.04.02.05.53.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Apr 2020 05:53:50 -0700 (PDT) Subject: Re: [PATCH 3/7] objtool: Add support for intra-function calls To: Alexandre Chartre , x86@kernel.org Cc: linux-kernel@vger.kernel.org, jpoimboe@redhat.com, peterz@infradead.org, tglx@linutronix.de References: <20200402082220.808-1-alexandre.chartre@oracle.com> <20200402082220.808-4-alexandre.chartre@oracle.com> From: Julien Thierry Message-ID: Date: Thu, 2 Apr 2020 13:53:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200402082220.808-4-alexandre.chartre@oracle.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). > 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 > --- > 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)? 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 " ? > + 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. > + } > + > + 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, -- Julien Thierry