From nobody Sun Nov 24 14:43:07 2024 Received: from mail.loongson.cn (mail.loongson.cn [114.242.206.163]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AA6FF1D5CD7 for ; Tue, 5 Nov 2024 12:40:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=114.242.206.163 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730810433; cv=none; b=Ll2ojV4HPZa7bcvDLogZbVSU9W+U6II/a0EOxUfj639H7PhMSAiSTqhhz4l+dkhGAwxU2/I8XooRTRbk3OcaMWGcl3OHgzIW88pyA+P///++6oNYELhz+3GMzFBbnGs1TF9YB62lO0FZWHZ45TDLImj6AtTIiGENO4u2CGragXI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730810433; c=relaxed/simple; bh=AJwHgU1lPUIK2aReyiUYS5P69puXM2GY8DxuNND1mWs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=C2KfdEigcwbc5UxA+uxUJ53gBxDNSxabYnfppGZEJxYFp241sFK4KzimbcjgMfEzPl5PmV/cwJFR3n+uhejupHObqSfx8L9tNvyUiSmRlNtRrIp9tLccK9GmYqJQkJsC2B15VQBgezKHC4UMpkBzpOItWn7PVkTTtlmJWLbUW5c= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn; spf=pass smtp.mailfrom=loongson.cn; arc=none smtp.client-ip=114.242.206.163 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=loongson.cn Received: from loongson.cn (unknown [113.200.148.30]) by gateway (Coremail) with SMTP id _____8AxbeLwESpnl7UxAA--.34025S3; Tue, 05 Nov 2024 20:39:12 +0800 (CST) Received: from linux.localdomain (unknown [113.200.148.30]) by front1 (Coremail) with SMTP id qMiowMBxrsLsESpnw4lCAA--.26454S6; Tue, 05 Nov 2024 20:39:12 +0800 (CST) From: Tiezhu Yang To: Huacai Chen , Josh Poimboeuf , Peter Zijlstra Cc: loongarch@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH v2 4/5] objtool/LoongArch: Add support for goto table Date: Tue, 5 Nov 2024 20:39:05 +0800 Message-ID: <20241105123906.26072-5-yangtiezhu@loongson.cn> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20241105123906.26072-1-yangtiezhu@loongson.cn> References: <20241105123906.26072-1-yangtiezhu@loongson.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: qMiowMBxrsLsESpnw4lCAA--.26454S6 X-CM-SenderInfo: p1dqw3xlh2x3gn0dqz5rrqw2lrqou0/ X-Coremail-Antispam: 1Uk129KBj93XoWxCw4rWw18Wr1fGr1kCw4kuFX_yoWrJw1UpF W3C345Kr45Xr1fWr47tay09ryaya1Igry7GrWDt348Aw43Xr1FyF1xtF90yFW8Wrs5Ar4I qr1rKr4UCF4DAacCm3ZEXasCq-sJn29KB7ZKAUJUUUUr529EdanIXcx71UUUUU7KY7ZEXa sCq-sGcSsGvfJ3Ic02F40EFcxC0VAKzVAqx4xG6I80ebIjqfuFe4nvWSU5nxnvy29KBjDU 0xBIdaVrnRJUUU9Fb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I20VC2zVCF04k26cxKx2 IYs7xG6rWj6s0DM7CIcVAFz4kK6r106r15M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48v e4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI 0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVW8Jr0_Cr1UM28EF7xvwVC2z280aVCY1x0267AK xVW8Jr0_Cr1UM2kKe7AKxVWUXVWUAwAS0I0E0xvYzxvE52x082IY62kv0487Mc804VCY07 AIYIkI8VC2zVCFFI0UMc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWU tVWrXwAv7VC2z280aVAFwI0_Gr0_Cr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcxkI7V AKI48JMxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMxCIbckI1I0E14v2 6r1Y6r17MI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17 CEb7AF67AKxVWUAVWUtwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r4j6ryUMIIF 0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIx AIcVC2z280aVAFwI0_Gr0_Cr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2 KfnxnUUI43ZEXa7IU8N6pPUUUUU== Content-Type: text/plain; charset="utf-8" The objtool program needs to analysis the control flow of each object file generated by compiler toolchain, it needs to know all the locations that a branch instruction may jump into, if a jump table is used, objtool has to correlate the jump instruction with the table. On x86 which is the only port supported by objtool before LoongArch, there is a relocation on the jump instruction and to the table directly. But on LoongArch, the relocation is on some kind of instruction prior to the jump instruction, and also with scheduling it is not easy to tell the offset of that instruction from the jump instruction. Furthermore, because LoongArch has -fsection-anchors (often enabled at -O1 or above) the relocation may actually points to a section anchor instead of the table itself. For the jump table of switch cases, a GCC patch "LoongArch: Add support to annotate tablejump" has been merged into the upstream mainline, it makes life much easier with the additional section ".discard.tablejump_annotate" which stores the jump info as pairs of addresses, each pair contains the address of jump instruction and the address of jump table. For the jump table of computed gotos, it is indeed not easy to implement in the compiler, especially if there is more than one computed goto in a function such as ___bpf_prog_run(). objdump kernel/bpf/core.o shows that there are many table jump instructions in ___bpf_prog_run(), but there are no relocations on the table jump instructions and to the table directly on LoongArch. Without the help of compiler, in order to figure out the address of goto table for the special case of ___bpf_prog_run(), since the instruction sequence is relatively single and stable, it makes sense to add a helper find_reloc_of_rodata_c_jump_table() to find the relocation which points to the section ".rodata..c_jump_table". If find_reloc_by_table_annotate() failed, it means there is no relocation info of switch table address in ".rela.discard.tablejump_annotate", then objtool may find the relocation info of goto table ".rodata..c_jump_table" with find_reloc_of_rodata_c_jump_table(). Signed-off-by: Tiezhu Yang --- tools/objtool/arch/loongarch/special.c | 28 ++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/tools/objtool/arch/loongarch/special.c b/tools/objtool/arch/lo= ongarch/special.c index 31e0f94e31e8..fe7413bcd98b 100644 --- a/tools/objtool/arch/loongarch/special.c +++ b/tools/objtool/arch/loongarch/special.c @@ -41,6 +41,27 @@ static struct reloc *find_reloc_by_table_annotate(struct= objtool_file *file, return NULL; } =20 +static struct reloc *find_reloc_of_rodata_c_jump_table(struct section *sec, + unsigned long offset) +{ + struct section *rsec; + struct reloc *reloc; + + rsec =3D sec->rsec; + if (!rsec) + return NULL; + + for_each_reloc(rsec, reloc) { + if (reloc_offset(reloc) > offset) + break; + + if (!strncmp(reloc->sym->sec->name, ".rodata..c_jump_table", 21)) + return reloc; + } + + return NULL; +} + struct reloc *arch_find_switch_table(struct objtool_file *file, struct instruction *insn) { @@ -50,8 +71,11 @@ struct reloc *arch_find_switch_table(struct objtool_file= *file, unsigned long table_offset; =20 annotate_reloc =3D find_reloc_by_table_annotate(file, insn); - if (!annotate_reloc) - return NULL; + if (!annotate_reloc) { + annotate_reloc =3D find_reloc_of_rodata_c_jump_table(insn->sec, insn->of= fset); + if (!annotate_reloc) + return NULL; + } =20 table_sec =3D annotate_reloc->sym->sec; if (annotate_reloc->sym->type =3D=3D STT_SECTION) --=20 2.42.0