From nobody Thu Apr 9 14:18:24 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8090ECAAA1 for ; Tue, 30 Aug 2022 10:50:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230042AbiH3KuQ (ORCPT ); Tue, 30 Aug 2022 06:50:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51380 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230000AbiH3KuA (ORCPT ); Tue, 30 Aug 2022 06:50:00 -0400 Received: from xry111.site (xry111.site [IPv6:2001:470:683e::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BB919FEF for ; Tue, 30 Aug 2022 03:49:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=xry111.site; s=default; t=1661856587; bh=CgtmaUw0UwaoZn+tYjzbKz/lFf1KH1RSTMazBd+mvWo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=S+zhDhRipw1yMd4IOtKMoMNQRQJG1G3mn5K6IrCkp27OQvIPYQKCasQPtz61T1oJH 279Yv/8gsLxtygbo45fJ5vqKwq1d8VcRBF73WWqpXM9J31OEA7dVhh8y68DwHVr39D oohqCuiEjtzHFDFuNhSTwEXBjdnat4yREszVBBh4= Received: from xry111-x57s1.. (unknown [IPv6:240e:358:11dd:1900:dc73:854d:832e:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-384) server-digest SHA384) (Client did not present a certificate) (Authenticated sender: xry111@xry111.site) by xry111.site (Postfix) with ESMTPSA id AACC5660A9; Tue, 30 Aug 2022 06:49:43 -0400 (EDT) From: Xi Ruoyao To: loongarch@lists.linux.dev Cc: linux-kernel@vger.kernel.org, WANG Xuerui , Huacai Chen , Youling Tang , Jinyang He , Xi Ruoyao Subject: [PATCH v7 2/5] LoongArch: Adjust symbol addressing for CONFIG_AS_HAS_EXPLICIT_RELOCS Date: Tue, 30 Aug 2022 18:48:03 +0800 Message-Id: <20220830104806.128365-3-xry111@xry111.site> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220830104806.128365-1-xry111@xry111.site> References: <20220830104806.128365-1-xry111@xry111.site> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" If explicit relocation hints is used by the toolchain, -Wa,-mla-* options will be useless for C code. Only use them for !CONFIG_AS_HAS_EXPLICIT_RELOCS. Replace "la" with "la.pcrel" in head.S to keep the semantic consistent with new and old toolchains for the low level startup code. For per-CPU variables, the "address" of the symbol is actually an offset from $r21. The value is nearing the loading address of main kernel image, but far from the address of modules. Use model("extreme") attibute to tell the compiler that a a PC-relative addressing with 32-bit offset is not sufficient for local per-CPU variables. The behavior with different assemblers and compilers are summarized in the following table: AS has CC has explicit reloc explicit reloc * Behavior =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D No No Use la.* macros. No change from Linux 6.0. -------------------------------------------------------------- No Yes Disable explicit reloc. No change from Linux 6.0. -------------------------------------------------------------- Yes No Not supported. -------------------------------------------------------------- Yes Yes Use explicit relocs. No -Wa,-mla* options. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D *: We assume CC must have model attribute if it has explicit reloc. Both features are added in GCC 13 development cycle, so any GCC release >=3D 13 should be OK. Using early GCC 13 development snapshots may produce modules with unsupported relocations. Link: https://sourceware.org/git/?p=3Dbinutils-gdb.git;a=3Dcommit;h=3Df0948= 2a Link: https://gcc.gnu.org/r13-1834 Link: https://gcc.gnu.org/r13-2199 Signed-off-by: Xi Ruoyao --- arch/loongarch/Makefile | 17 +++++++++++++++++ arch/loongarch/include/asm/percpu.h | 8 ++++++++ arch/loongarch/kernel/head.S | 10 +++++----- 3 files changed, 30 insertions(+), 5 deletions(-) diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile index 7051a95f7f31..92c4a52c4c3e 100644 --- a/arch/loongarch/Makefile +++ b/arch/loongarch/Makefile @@ -40,10 +40,27 @@ endif =20 cflags-y +=3D -G0 -pipe -msoft-float LDFLAGS_vmlinux +=3D -G0 -static -n -nostdlib + +# When the assembler supports explicit relocation hint, we must use it. +# GCC may have -mexplicit-relocs off by default if it was built with an old +# assembler, so we force it via an option. +# +# When the assembler does not supports explicit relocation hint, we can't = use +# it. Disable it if the compiler supports it. +# +# If you've seen "unknown reloc hint" message building the kernel and you = are +# now wondering why "-mexplicit-relocs" is not wrapped with cc-option: the +# combination of a "new" assembler and "old" compiler is not supported. E= ither +# upgrade the compiler or downgrade the assembler. +ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS +cflags-y +=3D -mexplicit-relocs +else +cflags-y +=3D $(call cc-option,-mno-explicit-relocs) KBUILD_AFLAGS_KERNEL +=3D -Wa,-mla-global-with-pcrel KBUILD_CFLAGS_KERNEL +=3D -Wa,-mla-global-with-pcrel KBUILD_AFLAGS_MODULE +=3D -Wa,-mla-global-with-abs KBUILD_CFLAGS_MODULE +=3D -fplt -Wa,-mla-global-with-abs,-mla-local-with-= abs +endif =20 cflags-y +=3D -ffreestanding cflags-y +=3D $(call cc-option, -mno-check-zero-division) diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/a= sm/percpu.h index 0bd6b0110198..dd7fcc553efa 100644 --- a/arch/loongarch/include/asm/percpu.h +++ b/arch/loongarch/include/asm/percpu.h @@ -8,6 +8,14 @@ #include #include =20 +#if defined(MODULE) && defined(CONFIG_AS_HAS_EXPLICIT_RELOCS) +/* The "address" (in fact, offset from $r21) of a per-CPU variable is close + * to the load address of main kernel image, but far from where the module= s are + * loaded. Tell the compiler this fact. + */ +# define PER_CPU_ATTRIBUTES __attribute__((model("extreme"))) +#endif + /* Use r21 for fast access */ register unsigned long __my_cpu_offset __asm__("$r21"); =20 diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S index 01bac62a6442..eb3f641d5915 100644 --- a/arch/loongarch/kernel/head.S +++ b/arch/loongarch/kernel/head.S @@ -55,17 +55,17 @@ SYM_CODE_START(kernel_entry) # kernel entry point li.w t0, 0x00 # FPE=3D0, SXE=3D0, ASXE=3D0, BTE=3D0 csrwr t0, LOONGARCH_CSR_EUEN =20 - la t0, __bss_start # clear .bss + la.pcrel t0, __bss_start # clear .bss st.d zero, t0, 0 - la t1, __bss_stop - LONGSIZE + la.pcrel t1, __bss_stop - LONGSIZE 1: addi.d t0, t0, LONGSIZE st.d zero, t0, 0 bne t0, t1, 1b =20 - la t0, fw_arg0 + la.pcrel t0, fw_arg0 st.d a0, t0, 0 # firmware arguments - la t0, fw_arg1 + la.pcrel t0, fw_arg1 st.d a1, t0, 0 =20 /* KSave3 used for percpu base, initialized as 0 */ @@ -73,7 +73,7 @@ SYM_CODE_START(kernel_entry) # kernel entry point /* GPR21 used for percpu base (runtime), initialized as 0 */ move u0, zero =20 - la tp, init_thread_union + la.pcrel tp, init_thread_union /* Set the SP after an empty pt_regs. */ PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE) PTR_ADD sp, sp, tp --=20 2.37.0