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{ "id": 2216000, "url": "http://patchwork.ozlabs.org/api/covers/2216000/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/cover/20260325160125.3469231-1-fmzakari@meta.com/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/projects/17/?format=api", "name": "GNU Compiler Collection", "link_name": "gcc", "list_id": "gcc-patches.gcc.gnu.org", "list_email": "gcc-patches@gcc.gnu.org", "web_url": null, "scm_url": null, "webscm_url": null, "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260325160125.3469231-1-fmzakari@meta.com>", "list_archive_url": null, "date": "2026-03-25T16:01:24", "name": "[0/1] libgcc: Add sdata8 binary search support to _Unwind_Find_FDE", "submitter": { "id": 92969, "url": "http://patchwork.ozlabs.org/api/people/92969/?format=api", "name": "Farid Zakaria", "email": "fmzakari@meta.com" }, "mbox": "http://patchwork.ozlabs.org/project/gcc/cover/20260325160125.3469231-1-fmzakari@meta.com/mbox/", "series": [ { "id": 497470, "url": "http://patchwork.ozlabs.org/api/series/497470/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=497470", "date": "2026-03-25T16:01:25", "name": "libgcc: Add sdata8 binary search support to _Unwind_Find_FDE", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/497470/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/covers/2216000/comments/", "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=meta.com header.i=@meta.com header.a=rsa-sha256\n header.s=s2048-2025-q2 header.b=NZQNFuvJ;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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a=rsa-sha256; d=sourceware.org; s=key; t=1774454501; cv=none;\n b=oK29CXrAJ1YKh8R4DrSwBINXtXUtTkcuP1AwPBpEXVjMk1ftgvp//I9wCn4va7GcJG94JTYL2a5NRx3Z6YHZn1/HlYys9STneUYZjtA30t84VEYESUnu0yWXBuv3E9riDzJfiC7iej5aGw5hZVZWBwIEKOyIe0si/n/Yax9yoc4=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1774454501; c=relaxed/simple;\n bh=4yqNfKusH8xZjE+Z4a7rh5zxEbh/INzmIuLxTUQBb34=;\n h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version;\n b=cCwpIB/D42eZmjThnS6RQTwBIPNNQVr8ip/wLirP1XUJB7EUhOKKiZBMefhQhgKRdtyjMrX08C5YKwIiw2Mu4QNAf1EPuZu/nsfcFX0WqHfN6UBt5AQVW8j8aRlLQ61pP5xevsg6jZb7Jj2vD/boLejMqPGxmYro6MzkhL4QRJ0=", "ARC-Authentication-Results": "i=1; server2.sourceware.org", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=meta.com; h=cc\n :content-transfer-encoding:content-type:date:from:message-id\n :mime-version:subject:to; s=s2048-2025-q2; bh=IJKcLbqlaQcX8wX5Vn\n UBlegdTfMTCZVU4xfGpMK4WII=; b=NZQNFuvJXl82ccG2x+5cpSTXmlhzW3/gdB\n myEDY8j60qZMiyoFnGLhfh7SnNP8Vzy1QGD9SwoHRT1Xh0IxwChq5ezDiGlUn47a\n Q6oEQ1R0MLGIaP8zJEgRRL2eXOHaUq1/SrfxMlvdzlbw2c2g1jXmg5cog7Aqo7M/\n X7Hg191zTHKsaXtWfjqXnTo8dvPPltWSyvWf7XIC3HFid3pPGlNzPRdja+lhz6rv\n an7FLprqclEwPs+hr0sjU8vvoIyHZ0e5LvIevvURJn4SdunH75j8sAC4tc7/gkPD\n PzDvQc8O+uuGnN29jMxLB8UCP3hyZdrPlvgzSF2x9QDN3Flr+Tsw==", "From": "Farid Zakaria <fmzakari@meta.com>", "To": "<gcc-patches@gcc.gnu.org>", "CC": "Farid Zakaria <fmzakari@meta.com>", "Subject": "[PATCH 0/1] libgcc: Add sdata8 binary search support to\n _Unwind_Find_FDE", "Date": "Wed, 25 Mar 2026 09:01:24 -0700", "Message-ID": "<20260325160125.3469231-1-fmzakari@meta.com>", "X-Mailer": "git-send-email 2.52.0", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "Content-Type": "text/plain", "X-Originating-IP": "[2620:10d:c085:108::150d]", "X-Proofpoint-Spam-Details-Enc": "AW1haW4tMjYwMzI1MDExNSBTYWx0ZWRfXyG/suaS+8MoC\n Omkci/n2WbzVlpua/zyTaI/L1Irt3D9yODz/Am3IzW152fgULBgjim8gbERweTfnYRGdY0JONaj\n zj8wCSk7oYfDA2obk2dUx0uVWBxykDSbmX7XYu2T0Mqn/sbYTKFUjUyQ/+dnr8sEbK6NJyj24+w\n 0kMYKCmfjNrB1iNkwkHsWIZVX4Su9SPkJh4K6OqAhJDrAnIisWzTOsUZG6kjmu9R2dTe4WEycuq\n yRKjJATm75X/foEM+j4olCQ1jWPmswA8Z8bnfU/sif5VY8hZw+kQWwC/xepohK248dU02pzmpDw\n YEH22wWkWzEyQKbAuvv3P4TI5UDD4XXOJQbG4yBvqRwcMDP88WtkLs399wfVI7sw6B6xIKnWNjj\n dcTvxj2m6b//2dKVdRjKsOMldEkWZWtgGq1EMA7giIKlXHGxDEn5UjxYpzuDGQkU3Knc14VY7+B\n ZfGwcpXqHbhRGjSe9Ew==", "X-Proofpoint-ORIG-GUID": "7TXA4v-e2y9ElDszkPJQT5CkiynlQ9AC", "X-Authority-Analysis": "v=2.4 cv=XJA9iAhE c=1 sm=1 tr=0 ts=69c406e4 cx=c_pps\n a=CB4LiSf2rd0gKozIdrpkBw==:117 a=CB4LiSf2rd0gKozIdrpkBw==:17\n a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22\n a=855S8uPTkML1Oy45N9_h:22 a=NEAV23lmAAAA:8 a=UD1FY8RiABmVuM7fjnkA:9", "X-Proofpoint-GUID": "7TXA4v-e2y9ElDszkPJQT5CkiynlQ9AC", "X-Proofpoint-Virus-Version": "vendor=baseguard\n engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49\n definitions=2026-03-25_04,2026-03-24_01,2025-10-01_01", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "The FDE lookup in unwind-dw2-fde-dip.c uses a binary search on the\n.eh_frame_hdr table, but only when the table encoding is\nDW_EH_PE_datarel | DW_EH_PE_sdata4 (8-byte entries). When\n-large-eh-encoding produces DW_EH_PE_datarel | DW_EH_PE_sdata8\n(16-byte entries), the code falls through to linear_search_fdes(),\nregressing FDE lookup from O(log N) to O(N).\n\nThis patch extends the binary search to also handle sdata8 table\nentries, maintaining O(log N) lookup for large binaries where\noffsets exceed 2GiB.\n\nWe recently added support in lld (LLVM) to support sdata8 for\neh_frame_hdr automatically regardless of code-model.\nhttps://github.com/llvm/llvm-project/pull/179089\n\nBenchmark results (FDE lookup with sdata8 encoding):\n\nBefore (falls through to linear_search_fdes):\n\n depth1(1) 719.49us 1.39K\n depth5(1) 723.31us 1.38K\n depth10(1) 726.60us 1.38K\n depth20(1) 739.54us 1.35K\n depth40(1) 779.26us 1.28K\n manyFdes(1) 13.02s 76.82m\n\nAfter (binary search for sdata8):\n\n depth1(1) 1.47us 679.29K\n depth5(1) 2.49us 402.15K\n depth10(1) 3.75us 266.96K\n depth20(1) 6.81us 146.93K\n depth40(1) 11.76us 85.03K\n manyFdes(1) 18.45ms 54.21\n\nThe manyFdes case improves from ~13s to ~18ms (~700x speedup).\n\nNote: there are no existing tests in the GCC testsuite for the\nsdata4 binary search path in find_fde_tail (the PT_GNU_EH_FRAME /\ndl_iterate_phdr path). \n\nBootstrapped and regression tested on x86_64-pc-linux-gnu.\n\nFarid Zakaria (1):\n libgcc: Add sdata8 binary search support to _Unwind_Find_FDE\n\n libgcc/unwind-dw2-fde-dip.c | 64 ++++++++++++++++++++++++++++---------\n 1 file changed, 49 insertions(+), 15 deletions(-)" }