[{"id":3680176,"web_url":"http://patchwork.ozlabs.org/comment/3680176/","msgid":"","list_archive_url":null,"date":"2026-04-22T01:30:32","subject":"Re: [PATCH v2 01/13] linux-user/mips, target/mips: honor MIPS_FIXADE\n for unaligned accesses","submitter":{"id":72104,"url":"http://patchwork.ozlabs.org/api/people/72104/","name":"Richard Henderson","email":"richard.henderson@linaro.org"},"content":"On 4/22/26 03:27, James Hilliard wrote:\n> Linux/MIPS enables software fixups for user-mode unaligned scalar\n> accesses by default through MIPS_FIXADE/TIF_FIXADE. QEMU linux-user did\n> not model that ABI, so MIPS guests took fatal AdEL/AdES exceptions\n> unless translation was forced to use unaligned host accesses.\n> \n> Replace the target-specific workaround with a generic MIPS linux-user\n> implementation:\n> \n> - key MIPS translation blocks on the linux-user unaligned policy,\n> - implement sysmips(MIPS_FIXADE) to toggle that policy,\n> - raise SIGBUS/BUS_ADRALN when fixups are disabled, and\n> - handle the existing sysmips(MIPS_ATOMIC_SET) and MIPS_FLUSH_CACHE\n> commands in the new target-side sysmips dispatcher.\n> \n> This makes the default behaviour match native Linux/MIPS more closely\n> and keeps the signal semantics consistent with the kernel ABI without\n> regressing other user-mode sysmips commands.\n> \n> Signed-off-by: James Hilliard \n\nThis patch does multiple things.\n\n(1) sysmips flush_cache.\n(2) sysmips atomic_set.\n(3) As stated, unaligned access controls.\n\nI suggest breaking it into 3 patches, in the order above.\nThat will add a bare-bones do_sysmips function in the first patch.\n\n\n> +#ifdef TARGET_NR_sysmips\n> +static abi_long do_sysmips_atomic_set(CPUArchState *env, abi_ulong addr,\n> + abi_long value)\n> +{\n> + uint32_t *ptr;\n> + abi_long old;\n> +\n> + if (addr & 3) {\n> + return -TARGET_EINVAL;\n> + }\n> +\n> + ptr = lock_user(VERIFY_WRITE, addr, sizeof(*ptr), true);\n> + if (!ptr) {\n> + return -TARGET_EINVAL;\n> + }\n> +\n> + old = tswap32(qatomic_xchg(ptr, tswap32((uint32_t)value)));\n> + unlock_user(ptr, addr, sizeof(*ptr));\n> +\n> + /*\n> + * MIPS uses a separate error flag, but the common linux-user syscall\n> + * path infers that flag from the return value. Successful atomic_set\n> + * results can overlap the target errno range, so write the result\n> + * registers here and ask the CPU loop to leave them alone.\n> + */\n> + if ((abi_ulong)old >= (abi_ulong)-TARGET_EDQUOT) {\n> + env->active_tc.gpr[2] = old;\n> + env->active_tc.gpr[7] = 0;\n> + return -QEMU_ESIGRETURN;\n> + }\n> +\n> + return old;\n\nThe comment is good, but the IF is unnecessary: always use the ESIGRETURN path.\n\n\nr~","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=nJDna/+Z;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists1p.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g0hXH6Tfzz1y2d\n\tfor ; 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