From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pj1-x102b.google.com (mail-pj1-x102b.google.com [IPv6:2607:f8b0:4864:20::102b]) by sourceware.org (Postfix) with ESMTPS id 928BB385840D for ; Wed, 24 Apr 2024 01:41:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 928BB385840D Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=linaro.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=linaro.org ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 928BB385840D Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2607:f8b0:4864:20::102b ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1713922891; cv=none; b=nYbPSpM+45BCy9Cmvos4IZFWuc6kbwAJGXS91Q4F4L10KAOYSXtJFKpY/yM30C23SJXiRA1yOfjFOJwo1rfLA2igQCOxH8k04YqFamzJupWHiNIaGX1Dp9qNnbgv74Jqo4N8wSMnGpDb3PRI7cnQzgV5+8vlMkX+0FmaKMAPBJU= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1713922891; c=relaxed/simple; bh=Z7+t0g5mGtUD9qoB5z7PUhKviYzKGLtFU583XLm8npU=; h=DKIM-Signature:Message-ID:Date:MIME-Version:Subject:To:From; b=BZrsrGyDNwCq1MiHF+aU+Q0GbcLDep7isVOiI+rlJx5NpZrQqzqP1t/hDF1PdfIvNKGaMWZks0sJm8yEKq5H6tzTcEYFR3jp/U1IPxqfqETqJbmzUvvbb53n9n/TLG6RwFtGI0qOVBCvej4LS7rj4JspEca7ocM58lxcIRBfnCY= ARC-Authentication-Results: i=1; server2.sourceware.org Received: by mail-pj1-x102b.google.com with SMTP id 98e67ed59e1d1-2a87bd53dc3so5134116a91.2 for ; Tue, 23 Apr 2024 18:41:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1713922888; x=1714527688; darn=sourceware.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:to:subject:user-agent:mime-version:date:message-id:from :to:cc:subject:date:message-id:reply-to; bh=rNLnc6ZUS1NREHbG1ZS9sTaOrafyIoRygu13V6hUDhs=; b=gH0RM66o9iY7Kl85Hr/sCjrsmy8ktCrE7GTJy6EReM/2pufxL4U83y/92VqT6kjIQe yJISc3rnwgD7gmFgRkTGhjFAO0W7/ZGxz+29x51AlLYZXnuD9Z7Hl0rDv+E43DkUohwy O09xtG1SgupzGchWSjB7pJBsZ1AlfyEBsyqCCYXY6qPDsXz7wlTyNVoJU4rvFjddlcXG k4Ip7tFg5WBEWthNUBubJqKaOUF+MzdV//rHh9FYGsV4ROdRNKPd7U2frKkGnM7LI37A 6jaIlNcmt8s3oRTVkWejhVgW/ZWJ5sMM8XggoaV/geoRlr7csLCNVlr0+db2ResRdTtg ec6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713922888; x=1714527688; h=content-transfer-encoding:in-reply-to:from:content-language :references:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rNLnc6ZUS1NREHbG1ZS9sTaOrafyIoRygu13V6hUDhs=; b=fpOGO/uxIfPR1eNhJ7hTCmLgudG4ZmpcA6s4/USTf48C8B8lS2Pc4kXD4DqIqu6ZAl YBKgvaIWUWEaAO+LI/w4fnA1xhlSKedGRE3xtncUZKW6DvA0OdAI84/m1pJZnHflQqFl lVWzVCpGag8NmNI6NsvET9UjaIDKkB/Y5S6srJ3jjgwvs8NLbpNtUK0DqnhDx4RxyLhW 35/5yxHUD+IJsl8anEnEclMM+ZX1tqxb5zAh4Efe1oyd3Thkblt8VjLN5e10IVT86Fhi vPchKFdU+gpnYIGKCAI8jKsYkcyn3L1hd+yRdWTA92Mm21rtrwQpZX0uszeaTgur4wRM qiAA== X-Forwarded-Encrypted: i=1; AJvYcCWookCOFlbrzc1VT4wNaplQfcCmqKKrFM79mvS/RPGe8t7WLXcK43TCnHpNF9k84HTdU+Gs1VLdGBXqg5DMnLWy774DpoZ8vSu9 X-Gm-Message-State: AOJu0Yx3cqfRCZID9A3JdwGx/QRHwDtdpYYxk0/zT2+D5SSkUWc6tpqA mOfW+7tklR9IcmqRWTsRVjPFbwPdkreNMwRKO+sfjwMysIcbG5B7XV1I+XiC/Vm5aH0J/wIoEAQ 0 X-Google-Smtp-Source: AGHT+IGZATlCJnqeYm/VfuQfj9ZEdtFZpZmhMTZCxDaNZjeIESv9Qg+/rEAyX+H9QcG5kLqM0GK1ZA== X-Received: by 2002:a17:90b:1d88:b0:2ae:bbf7:30fa with SMTP id pf8-20020a17090b1d8800b002aebbf730famr911672pjb.3.1713922888562; Tue, 23 Apr 2024 18:41:28 -0700 (PDT) Received: from [192.168.91.227] ([156.19.246.23]) by smtp.gmail.com with ESMTPSA id x21-20020a17090a531500b002a71f11ddd4sm10248601pjh.15.2024.04.23.18.41.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Apr 2024 18:41:28 -0700 (PDT) Message-ID: Date: Tue, 23 Apr 2024 18:41:20 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Maybe we should get rid of ifuncs To: Zack Weinberg , libc-alpha@sourceware.org References: Content-Language: en-US From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 4/23/24 11:14, Zack Weinberg wrote: > (2) Are there existing ifuncs that perform CPU-capability-based > function selection that*could not* be replaced with an array of bit > vectors like what I sketched in the previous paragraph? How much is in actual use, I have no idea. However: Even x86 cpuid generates a staggeringly large bit vector. Similarly the arm cpu id register space (some of which is reflected in hwcap; all of which is available via el0 trap-to-read-filtered-value). In principal I think the idea of declarative selection is good. It's what I would have chosen once upon a time if I had been clever enough to invent the correct (almost certainly target-specific) data structure(s). r~