From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=UeFy=DY=redhat.com=fweimer@sourceware.org>
Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124])
	by sourceware.org (Postfix) with ESMTPS id 594C13858C41
	for <libc-alpha@sourceware.org>; Mon,  7 Aug 2023 22:21:19 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 594C13858C41
Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com
Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;
	s=mimecast20190719; t=1691446879;
	h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
	 to:to:cc:cc:mime-version:mime-version:content-type:content-type:
	 in-reply-to:in-reply-to:references:references;
	bh=AKC1UnYITiv+qlCjYHui+mwIf6zlpALXax9yUql3FNc=;
	b=eTPuwirMil25HUK2wHbwW1XCEYnk/WpXKpGA0udR/IF+Rh8zwlH6WnFasnNVADyRnCaSDM
	xAddM/Gd54r/GJxuVv8yh27LpHmMzt92M2bPJ76hdunTAWTNFyRJPAvSBQq9kr+bW7gAz+
	4ok8gl7TIGosQr9zPb2B39pW5/vL2Mw=
Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com
 [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS
 (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 us-mta-526-mpBtg3BiNNy9iVW08fj28g-1; Mon, 07 Aug 2023 18:21:14 -0400
X-MC-Unique: mpBtg3BiNNy9iVW08fj28g-1
Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7])
	(using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
	(No client certificate requested)
	by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7496C800303;
	Mon,  7 Aug 2023 22:21:14 +0000 (UTC)
Received: from oldenburg.str.redhat.com (unknown [10.2.16.12])
	by smtp.corp.redhat.com (Postfix) with ESMTPS id 90BD2140E950;
	Mon,  7 Aug 2023 22:21:13 +0000 (UTC)
From: Florian Weimer <fweimer@redhat.com>
To: Evan Green <evan@rivosinc.com>
Cc: Richard Henderson <richard.henderson@linaro.org>,
  libc-alpha@sourceware.org,  slewis@rivosinc.com,  palmer@rivosinc.com,
  vineetg@rivosinc.com
Subject: Re: [PATCH v6 5/5] riscv: Add and use alignment-ignorant memcpy
References: <20230802155903.2552780-1-evan@rivosinc.com>
	<20230802155903.2552780-6-evan@rivosinc.com>
	<87il9w37vi.fsf@oldenburg.str.redhat.com>
	<6f0911c6-b24b-444c-4b4b-a62e49a51734@linaro.org>
	<CALs-HssWPZoMpuqxfEg3+bVdRgvm03ZYBPrAAjKXx=ojsoemYw@mail.gmail.com>
	<548fc7d5-6225-69e7-f4a7-47669d2fdbd5@linaro.org>
	<CALs-HsueMLAs7tzkz-bOSi9j+eFKbyJwQZ-Pi60BN7+SvYKSTw@mail.gmail.com>
Date: Tue, 08 Aug 2023 00:21:12 +0200
In-Reply-To: <CALs-HsueMLAs7tzkz-bOSi9j+eFKbyJwQZ-Pi60BN7+SvYKSTw@mail.gmail.com>
	(Evan Green's message of "Mon, 7 Aug 2023 15:10:51 -0700")
Message-ID: <878ramebon.fsf@oldenburg.str.redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux)
MIME-Version: 1.0
X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7
X-Mimecast-Spam-Score: 0
X-Mimecast-Originator: redhat.com
Content-Type: text/plain
X-Spam-Status: No, score=-4.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,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: <libc-alpha.sourceware.org>

* Evan Green:

> Right, this is what we had in the previous iteration of this series,
> and it did work ok. But it wasn't as good since it meant ifunc
> selectors always got stuck in the null/fallback case and were forced
> to make the syscall. With this mechanism they get to take advantage of
> the vDSO.

The system call is only required when the IFUNC resolver is called in
advance of relocation.  In most cases, the ELF dependencies work as
expected and ensure that the object containing the IFUNC resolver is
already relocation, and use of the fallback is avoided.

Thanks,
Florian