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 90AEB4629F for ; Sat, 13 Jan 2024 00:57:35 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 1261268CE17; Sat, 13 Jan 2024 02:57:33 +0200 (EET) Received: from btbn.de (btbn.de [144.76.60.213]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 5E98568CCA8 for ; Sat, 13 Jan 2024 02:57:26 +0200 (EET) Received: from [authenticated] by btbn.de (Postfix) with ESMTPSA id 6064527FAA8DE; Sat, 13 Jan 2024 01:57:25 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rothenpieler.org; s=mail; t=1705107445; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5p/EIn3ysJ0DLh6QNa1f4xd41IixSd54tN0WCH4uC3c=; b=LJOj28Nk3bfMGmvYbl3PhoV6BdvheXy6smxTtf6fAAWb3RaTBmaAFQ4ZNvTjL0zXIhJxKw RnCwKaKdNLSpCRNn3q43qTjUyRdinW5R1W51kUKRBSmIBlHmPdSoBDjDe34stw+5TDBivE 6V41ozoqaWBCMFrb40pB113MVox4PtLei1bTiHuS6DT5+gLW7LesJ3k97y7tyjt368/XWu Aw08C4E/Q9SxDpOVyMKWWWkAPknQgNyb+qvf5JHSUYbNbOr+BwBRo347Zo7hlykUSip/AK uRuc/tkbE2GdSZKQjvJpamJAtmwCWmtBo6/OVYKZSM1S7BXsMA2VYGL2yI5ysw== From: Timo Rothenpieler To: ffmpeg-devel@ffmpeg.org Date: Sat, 13 Jan 2024 01:57:16 +0100 Message-Id: <20240113005716.16018-1-timo@rothenpieler.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <9ecc9fe5-d75b-41f7-8476-2e69c58951fd@rothenpieler.org> References: <9ecc9fe5-d75b-41f7-8476-2e69c58951fd@rothenpieler.org> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH] avutil/mem: limit alignment to maximum simg align 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 Cc: Timo Rothenpieler Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: 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. This patch limits the maximum alignment to the maximum possible simd alignment according to configure. While not perfect, it at the very least gets rid of a lot of UB, by matching up the maximum DECLARE_ALIGNED value with the alignment of heap allocations done by lavu. --- libavutil/mem.c | 2 +- libavutil/mem_internal.h | 20 +++++++++++--------- 2 files changed, 12 insertions(+), 10 deletions(-) diff --git a/libavutil/mem.c b/libavutil/mem.c index 36b8940a0c..62163b4cb3 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_SIMD_ALIGN_64 ? 64 : (HAVE_SIMD_ALIGN_32 ? 32 : 16)) /* NOTE: if you want to override these functions with your own * implementations (not recommended) you have to link libav* as diff --git a/libavutil/mem_internal.h b/libavutil/mem_internal.h index 2448c606f1..ddd3c24806 100644 --- a/libavutil/mem_internal.h +++ b/libavutil/mem_internal.h @@ -75,22 +75,24 @@ * @param v Name of the variable */ +#define MAX_ALIGNMENT (HAVE_SIMD_ALIGN_64 ? 64 : (HAVE_SIMD_ALIGN_32 ? 32 : 16)) + #if defined(__INTEL_COMPILER) && __INTEL_COMPILER < 1110 || defined(__SUNPRO_C) - #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (n))) v - #define DECLARE_ASM_ALIGNED(n,t,v) t __attribute__ ((aligned (n))) v - #define DECLARE_ASM_CONST(n,t,v) const t __attribute__ ((aligned (n))) v + #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (FFMIN(n, MAX_ALIGNMENT)))) v + #define DECLARE_ASM_ALIGNED(n,t,v) t __attribute__ ((aligned (FFMIN(n, MAX_ALIGNMENT)))) v + #define DECLARE_ASM_CONST(n,t,v) const t __attribute__ ((aligned (FFMIN(n, MAX_ALIGNMENT)))) v #elif defined(__DJGPP__) #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (FFMIN(n, 16)))) v #define DECLARE_ASM_ALIGNED(n,t,v) t av_used __attribute__ ((aligned (FFMIN(n, 16)))) v #define DECLARE_ASM_CONST(n,t,v) static const t av_used __attribute__ ((aligned (FFMIN(n, 16)))) v #elif defined(__GNUC__) || defined(__clang__) - #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (n))) v - #define DECLARE_ASM_ALIGNED(n,t,v) t av_used __attribute__ ((aligned (n))) v - #define DECLARE_ASM_CONST(n,t,v) static const t av_used __attribute__ ((aligned (n))) v + #define DECLARE_ALIGNED(n,t,v) t __attribute__ ((aligned (FFMIN(n, MAX_ALIGNMENT)))) v + #define DECLARE_ASM_ALIGNED(n,t,v) t av_used __attribute__ ((aligned (FFMIN(n, MAX_ALIGNMENT)))) v + #define DECLARE_ASM_CONST(n,t,v) static const t av_used __attribute__ ((aligned (FFMIN(n, MAX_ALIGNMENT)))) v #elif defined(_MSC_VER) - #define DECLARE_ALIGNED(n,t,v) __declspec(align(n)) t v - #define DECLARE_ASM_ALIGNED(n,t,v) __declspec(align(n)) t v - #define DECLARE_ASM_CONST(n,t,v) __declspec(align(n)) static const t v + #define DECLARE_ALIGNED(n,t,v) __declspec(align(FFMIN(n, MAX_ALIGNMENT))) t v + #define DECLARE_ASM_ALIGNED(n,t,v) __declspec(align(FFMIN(n, MAX_ALIGNMENT))) t v + #define DECLARE_ASM_CONST(n,t,v) __declspec(align(FFMIN(n, MAX_ALIGNMENT))) static const t v #else #define DECLARE_ALIGNED(n,t,v) t v #define DECLARE_ASM_ALIGNED(n,t,v) t v -- 2.34.1 _______________________________________________ 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".