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[173.52.224.122]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c5b93485f7sm329639285a.74.2025.03.22.21.54.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 22 Mar 2025 21:54:31 -0700 (PDT) From: Nick Terrell To: linux-kernel@vger.kernel.org Cc: Nick Terrell , Nick Terrell , Kernel Team , David Sterba , Nick Terrell , Ingo Molnar , Michael Kelley , Borislav Petkov Subject: [PATCH] zstd: Work around gcc segfault on versions older than 11.4 Date: Sat, 22 Mar 2025 22:07:49 -0700 Message-ID: <20250323050749.165863-1-nickrterrell@gmail.com> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Nick Terrell Older gcc version segfault in zstd code as of 9d7de2aa8b41 on x86. This see= ms to be triggered by some other compilation changes. But it can be worked around by disabling DYNAMIC_BMI2 for older gcc compilers. The original suggested patch in the thread suggested gating on gcc >=3D 11, but there is only positive confirmation that gcc 11.4 and later succeed, so I'm being slightly more conservative. This will reduce performance of Zstandard decoding by ~10% if using a gcc version older than 11.4, and the binary is not compiled with BMI2 support at compile time. I've compiled & run basic tests for gcc-9 and gcc-14.2. I've reproed the gcc segfault before the fix, and it compiles after. Link: https://lore.kernel.org/lkml/SN6PR02MB415723FBCD79365E8D72CA5FD4D82@S= N6PR02MB4157.namprd02.prod.outlook.com/ CC: Ingo Molnar CC: Michael Kelley CC: Borislav Petkov Signed-off-by: Nick Terrell --- lib/zstd/common/portability_macros.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/lib/zstd/common/portability_macros.h b/lib/zstd/common/portabi= lity_macros.h index 05286af72683..efae9465d57d 100644 --- a/lib/zstd/common/portability_macros.h +++ b/lib/zstd/common/portability_macros.h @@ -56,12 +56,14 @@ =20 =20 /* Enable runtime BMI2 dispatch based on the CPU. - * Enabled for clang & gcc >=3D4.8 on x86 when BMI2 isn't enabled by defau= lt. + * Enabled for clang & gcc >=3D 11.4 on x86 when BMI2 isn't enabled by def= ault. + * Disabled for gcc < 11.4 because of a segfault while compiling + * HUF_compress1X_usingCTable_internal_body(). */ #ifndef DYNAMIC_BMI2 # if ((defined(__clang__) && __has_attribute(__target__)) \ || (defined(__GNUC__) \ - && (__GNUC__ >=3D 5 || (__GNUC__ =3D=3D 4 && __GNUC_MINOR__ >=3D= 8)))) \ + && (__GNUC__ >=3D 12 || (__GNUC__ =3D=3D 11 && __GNUC_MINOR__ >= =3D 4)))) \ && (defined(__i386__) || defined(__x86_64__) || defined(_M_IX86) || = defined(_M_X64)) \ && !defined(__BMI2__) # define DYNAMIC_BMI2 1 --=20 2.48.1