From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id E7C5848503 for ; Wed, 6 Dec 2023 12:26:54 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id E1F6168CF7B; Wed, 6 Dec 2023 14:26:53 +0200 (EET) Received: from btbn.de (btbn.de [136.243.74.85]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 6108D68CEB1 for ; Wed, 6 Dec 2023 14:26:49 +0200 (EET) Received: from [authenticated] by btbn.de (Postfix) with ESMTPSA id 2483D47D282 for ; Wed, 6 Dec 2023 13:26:49 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rothenpieler.org; s=mail; t=1701865609; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ao46S5oS8OqTol8YdkeK2q9K1tJolGjS1qEZP7Gue90=; b=Tepfw2zG4yiTlqZKR9lHt25rHciYEyGOeJmK1AJWummB3pAfeuHepGXd4u5Kg4QX7wtUIZ ahUR0E0m08DrPX0Y4ukBULOn1nwplv+TQxLg0L8tjbh1HmhA7LLyjNJ3FlG4QKE5/Zvf00 WR2V3eVlJywsmnMV6y6ixSMb9njmxsnx0wqshWrZvjeJz42nJH2peMCkI4YNCNrJqfk+Uc RDhDBWn0LebqoXZTmaZXqMyyrLv4lbs1v9OrmnBIpLWqv4+i7YyNbceOzN0drD0U7D9JcA QRX0u6qNlOdGjHohOKLeLhITn9IY1TWSy75cYJAer8WrrzfnncBywr2KoBZJUg== Message-ID: Date: Wed, 6 Dec 2023 13:27:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US, de-DE To: ffmpeg-devel@ffmpeg.org References: <20231203201027.2255-1-timo@rothenpieler.org> From: Timo Rothenpieler In-Reply-To: <20231203201027.2255-1-timo@rothenpieler.org> Subject: Re: [FFmpeg-devel] [PATCH] avutil/mem: always align by at least 32 bytes X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: On 03/12/2023 21:10, Timo Rothenpieler wrote: > FFmpeg has instances of DECLARE_ALIGNED(32, ...) in a lot of structs, > which then end up heap-allocated. > By declaring any variable in a struct, or tree of structs, to be 32 byte > aligned, it allows the compiler to safely assume the entire struct > itself is also 32 byte aligned. > > This might make the compiler emit code which straight up crashes or > misbehaves in other ways, and at least in one instances is now > documented to actually do (see ticket 10549 on trac). > The issue there is that an unrelated variable in SingleChannelElement is > declared to have an alignment of 32 bytes. So if the compiler does a copy > in decode_cpe() with avx instructions, but ffmpeg is built with > --disable-avx, this results in a crash, since the memory is only 16 byte > aligned. > Mind you, even if the compiler does not emit avx instructions, the code > is still invalid and could misbehave. It just happens not to. Declaring > any variable in a struct with a 32 byte alignment promises 32 byte > alignment of the whole struct to the compiler. > > Instead of now going through all instances of variables in structs > being declared as 32 byte aligned, this patch bumps the minimum alignment > to 32 bytes. > --- > libavutil/mem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/libavutil/mem.c b/libavutil/mem.c > index 36b8940a0c..26a9b9753b 100644 > --- a/libavutil/mem.c > +++ b/libavutil/mem.c > @@ -62,7 +62,7 @@ void free(void *ptr); > > #endif /* MALLOC_PREFIX */ > > -#define ALIGN (HAVE_AVX512 ? 64 : (HAVE_AVX ? 32 : 16)) > +#define ALIGN (HAVE_AVX512 ? 64 : 32) > > /* NOTE: if you want to override these functions with your own > * implementations (not recommended) you have to link libav* as ping _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".