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 ESMTPS id 632F84D96D for ; Wed, 26 Feb 2025 19:44:57 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 5E56968C8AC; Wed, 26 Feb 2025 21:44:53 +0200 (EET) Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id F289F68C2ED for ; Wed, 26 Feb 2025 21:44:46 +0200 (EET) Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-6f3ff1ff117so3602887b3.0 for ; Wed, 26 Feb 2025 11:44:46 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740599085; x=1741203885; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=g1xG2BwUHwAVwGs3/fulHYF0J1EyFJsKdQHYIUF6QgI=; b=bD8TISltddpeK1N6bJuZ69aDrDCBTbzVtboZ+UqIPYgFrwrO6Z4BkdZGzULr8tcILh faioO0IOdygmtdrndBRVMUnKSrCybxtNonUMrhFU8FOzFkJyzoNp3a7gPC+aesn3E5o2 ChjP4f+6QjsGeZCveajhYf0646XU/VazAhqILo93YMFMvy65sr1EQWN9ftb+YntJgTL/ ENDKkizjMagBxQ5st9liYhqkJ+jepzLd6f87hnMWz7k/W/f6y1K8aOXBVl8HzdA+kaLx GxhykijWk2x983dHsOUCsIref3fT+lp0MlxM0AxxrcShP/zHOo6xGB1rHTB1io1Wvcu0 GNyg== X-Gm-Message-State: AOJu0YxHlLF4cFOknmu/daqF/5D8WbuK3KtmRhThWqoBTlti36kJDJaN SKZcMkQFc/hb5wf+vzytUC+aupifHJTEHuufh1mSI6BfK5nutpelH1kgJ20ojpd/+bG+pxKHnNJ 1O68jNuK7aFeBohCejRJ3OvLuxyLuqDBOKs9+1tmyohnqo+NFxDE7kxTGPJ+LNF8Z2qjPBjokX/ hFBUornsj2kKj5XxoJtoioijU= X-Google-Smtp-Source: AGHT+IEek5qrSrAKX8nQf7WDfizgjWWiBySVPkJTNrI2dB4NSKqshTeWEg5mTy8GdmuAiAAxXLRv73tG X-Received: from ywbjd12.prod.google.com ([2002:a05:690c:6f0c:b0:6f9:4a3e:e1d1]) (user=prka job=prod-delivery.src-stubby-dispatcher) by 2002:a05:690c:3585:b0:6fb:9389:3cde with SMTP id 00721157ae682-6fd109aad0cmr76394117b3.3.1740599085307; Wed, 26 Feb 2025 11:44:45 -0800 (PST) Date: Wed, 26 Feb 2025 19:44:37 +0000 In-Reply-To: <20250225213717.3373852-1-prka@google.com> Mime-Version: 1.0 References: <20250225213717.3373852-1-prka@google.com> X-Mailer: git-send-email 2.48.1.658.g4767266eb4-goog Message-ID: <20250226194437.121075-1-prka@google.com> To: ffmpeg-devel@ffmpeg.org Subject: [FFmpeg-devel] [PATCH] Mark C globals with small code model 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: , From: Pranav Kant via ffmpeg-devel Reply-To: FFmpeg development discussions and patches Cc: Pranav Kant 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: By default, all globals in C/C++ compiled by clang are allocated in non-large data sections. See [1] for background on code models. For PIC (Position independent code), this is fine as long as binary is small but as binary size increases, users maybe want to use medium/large code models (-mcmodel=medium) which moves data in to large sections. As data in these large sections cannot be accessed using PIC code anymore (as it may be too far away), compiler ends up using a different instruction sequence when building C/C++ code -- using GOT to access these globals (which can be relaxed by linker at link time if binary ends up being smaller). However, assembly files continue to access these globals defined in C/C++ files using older (and invalid instruction sequence). So, we mark all such globals with an attribute that forces them to be allocated in small sections allowing them to validly be accessed from the assembly code. This patch should not have any affect on builds that use small code model, which is the default mode. [1] https://eli.thegreenplace.net/2012/01/03/understanding-the-x64-code-models Signed-off-by: Pranav Kant --- libavcodec/ac3dsp.c | 2 ++ libavcodec/cabac.c | 2 ++ libavcodec/x86/constants.c | 8 ++++++++ libavutil/attributes_internal.h | 15 +++++++++++++++ 4 files changed, 27 insertions(+) diff --git a/libavcodec/ac3dsp.c b/libavcodec/ac3dsp.c index 730fa70fff..d16b6c24c3 100644 --- a/libavcodec/ac3dsp.c +++ b/libavcodec/ac3dsp.c @@ -25,6 +25,7 @@ #include "config.h" #include "libavutil/attributes.h" +#include "libavutil/attributes_internal.h" #include "libavutil/common.h" #include "libavutil/intmath.h" #include "libavutil/mem_internal.h" @@ -104,6 +105,7 @@ static void ac3_update_bap_counts_c(uint16_t mant_cnt[16], uint8_t *bap, mant_cnt[bap[len]]++; } +attribute_mcmodel_small DECLARE_ALIGNED(16, const uint16_t, ff_ac3_bap_bits)[16] = { 0, 0, 0, 3, 0, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16 }; diff --git a/libavcodec/cabac.c b/libavcodec/cabac.c index 7d41cd2ae6..b8c6db29a2 100644 --- a/libavcodec/cabac.c +++ b/libavcodec/cabac.c @@ -24,11 +24,13 @@ * Context Adaptive Binary Arithmetic Coder. */ +#include "libavutil/attributes_internal.h" #include "libavutil/error.h" #include "libavutil/mem_internal.h" #include "cabac.h" +attribute_mcmodel_small DECLARE_ASM_ALIGNED(1, const uint8_t, ff_h264_cabac_tables)[512 + 4*2*64 + 4*64 + 63] = { 9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5, 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4, diff --git a/libavcodec/x86/constants.c b/libavcodec/x86/constants.c index bc7f2b17b8..347b7dd1d3 100644 --- a/libavcodec/x86/constants.c +++ b/libavcodec/x86/constants.c @@ -18,17 +18,21 @@ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ +#include "libavutil/attributes_internal.h" #include "libavutil/mem_internal.h" #include "libavutil/x86/asm.h" // for xmm_reg #include "constants.h" +attribute_mcmodel_small DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1) = { 0x0001000100010001ULL, 0x0001000100010001ULL, 0x0001000100010001ULL, 0x0001000100010001ULL }; DECLARE_ALIGNED(32, const ymm_reg, ff_pw_2) = { 0x0002000200020002ULL, 0x0002000200020002ULL, 0x0002000200020002ULL, 0x0002000200020002ULL }; DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_3) = { 0x0003000300030003ULL, 0x0003000300030003ULL }; +attribute_mcmodel_small DECLARE_ASM_ALIGNED(32, const ymm_reg, ff_pw_4) = { 0x0004000400040004ULL, 0x0004000400040004ULL, 0x0004000400040004ULL, 0x0004000400040004ULL }; +attribute_mcmodel_small DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_5) = { 0x0005000500050005ULL, 0x0005000500050005ULL }; DECLARE_ALIGNED(16, const xmm_reg, ff_pw_8) = { 0x0008000800080008ULL, 0x0008000800080008ULL }; DECLARE_ASM_ALIGNED(16, const xmm_reg, ff_pw_9) = { 0x0009000900090009ULL, 0x0009000900090009ULL }; @@ -49,6 +53,7 @@ DECLARE_ALIGNED(32, const ymm_reg, ff_pw_256) = { 0x0100010001000100ULL, 0x010 DECLARE_ALIGNED(32, const ymm_reg, ff_pw_512) = { 0x0200020002000200ULL, 0x0200020002000200ULL, 0x0200020002000200ULL, 0x0200020002000200ULL }; DECLARE_ALIGNED(16, const xmm_reg, ff_pw_1019) = { 0x03FB03FB03FB03FBULL, 0x03FB03FB03FB03FBULL }; +attribute_mcmodel_small DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1023) = { 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL, 0x03ff03ff03ff03ffULL}; DECLARE_ALIGNED(32, const ymm_reg, ff_pw_1024) = { 0x0400040004000400ULL, 0x0400040004000400ULL, @@ -66,13 +71,16 @@ DECLARE_ALIGNED(32, const ymm_reg, ff_pw_m1) = { 0xFFFFFFFFFFFFFFFFULL, 0xFFF DECLARE_ALIGNED(32, const ymm_reg, ff_pb_0) = { 0x0000000000000000ULL, 0x0000000000000000ULL, 0x0000000000000000ULL, 0x0000000000000000ULL }; +attribute_mcmodel_small DECLARE_ALIGNED(32, const ymm_reg, ff_pb_1) = { 0x0101010101010101ULL, 0x0101010101010101ULL, 0x0101010101010101ULL, 0x0101010101010101ULL }; DECLARE_ALIGNED(32, const ymm_reg, ff_pb_2) = { 0x0202020202020202ULL, 0x0202020202020202ULL, 0x0202020202020202ULL, 0x0202020202020202ULL }; +attribute_mcmodel_small DECLARE_ALIGNED(32, const ymm_reg, ff_pb_3) = { 0x0303030303030303ULL, 0x0303030303030303ULL, 0x0303030303030303ULL, 0x0303030303030303ULL }; DECLARE_ALIGNED(32, const xmm_reg, ff_pb_15) = { 0x0F0F0F0F0F0F0F0FULL, 0x0F0F0F0F0F0F0F0FULL }; +attribute_mcmodel_small DECLARE_ALIGNED(32, const ymm_reg, ff_pb_80) = { 0x8080808080808080ULL, 0x8080808080808080ULL, 0x8080808080808080ULL, 0x8080808080808080ULL }; DECLARE_ALIGNED(32, const ymm_reg, ff_pb_FE) = { 0xFEFEFEFEFEFEFEFEULL, 0xFEFEFEFEFEFEFEFEULL, diff --git a/libavutil/attributes_internal.h b/libavutil/attributes_internal.h index 3df1ee6af3..0c40e6461f 100644 --- a/libavutil/attributes_internal.h +++ b/libavutil/attributes_internal.h @@ -31,4 +31,19 @@ # define FF_VISIBILITY_POP_HIDDEN #endif +/** + * Some globals defined in C files are used from hardcoded asm that assumes small + * code model (that is, accessing these globals without GOT). This is a problem + * when FFMpeg is built with medium code model (-mcmodel=medium) which allocates + * all globals in a data section that's unreachable with PC relative instructions + * (small code model instruction sequence). We mark all such globals with this + * attribute_mcmodel_small to ensure assembly accessible globals continue to be + * allocated in sections reachable from PC relative instructions. + */ +#if ARCH_X86_64 && defined(__ELF__) && __has_attribute(model) +# define attribute_mcmodel_small __attribute__(model("small")) +#else +# define attribute_mcmodel_small +#endif + #endif /* AVUTIL_ATTRIBUTES_INTERNAL_H */ -- 2.48.1.658.g4767266eb4-goog _______________________________________________ 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".