From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 16746 invoked from network); 1 Dec 2020 14:38:03 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 1 Dec 2020 14:38:03 -0000 Received: (qmail 26128 invoked by uid 550); 1 Dec 2020 14:37:59 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 25732 invoked from network); 1 Dec 2020 14:36:53 -0000 From: Marius Hillenbrand To: musl@lists.openwall.com Cc: Marius Hillenbrand Date: Tue, 1 Dec 2020 15:36:34 +0100 Message-Id: <20201201143634.13419-1-mhillen@linux.ibm.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [musl] [PATCH] s390x: derive float_t from compiler or default to float Hi, float_t should represent the type that is used to evaluate float expressions internally. On s390(x), float_t is currently set to double. In contrast, the isa supports single-precision float operations and compilers by default evaluate float in single precision, which violates the C standard (sections 5.2.4.2.2 and 7.12 in C11/C17). With -fexcess-precision=standard, gcc evaluates float in double precision, which aligns with the standard yet at the cost of added conversion instructions. To improve standards compliance, this patch changes the definition of float_t to be derived from the compiler's __FLT_EVAL_METHOD__. The port of glibc to s390 incorrectly deferred to the generic definitions which, back then, tied float_t to double. Since then, this definition has been kept to avoid ABI changes, most recently in the refactoring of float_t into bits/flt-eval-method.h https://sourceware.org/legacy-ml/libc-alpha/2016-11/msg00903.html and the discussion around https://gcc.gnu.org/legacy-ml/gcc-patches/2016-09/msg02392.html musl apparently adopted the definition from glibc. Given the performance overhead and reduced standards compliance, I have reevaluated cleaning up the special behavior on s390x. I found only two packages, ImageMagick and clucene, that use float_t in their API, out of >130k Debian source packages scanned. To avoid breaking ABI changes, I patched these packages to avoid their reliance on float_t (in ImageMagick since 7.0.10-39, patch in https://github.com/ImageMagick/ImageMagick/pull/2832 - patch for clucene in https://sourceforge.net/p/clucene/bugs/233). gcc-11 will drop the special case to retrofit double precision behavior for -fexcess-precision=standard so that __FLT_EVAL_METHOD__ will be 0 on s390x in any scenario. https://gcc.gnu.org/pipermail/gcc-patches/2020-November/560224.html https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=a5dd6b69fcbe74c02d4821ac2daf2b8c9f819f6e glibc 2.33 will most likely adopt the same behavior as in this patch, so that float_t will eventually be float on s390x in any scenario. https://sourceware.org/pipermail/libc-alpha/2020-November/120212.html Testing with libc-test showed no regressions. Failing testcases src/math/lgammaf[_r].exe succeed with the patch. Please review and consider merging this patch. Marius --->8------>8------>8------>8------>8------>8------>8------>8--- float_t should represent the type that is used to evaluate float expressions internally. On s390(x), float_t is currently set to double. In contrast, the isa supports single-precision float operations and compilers by default evaluate float in single precision, which violates the C standard (sections 5.2.4.2.2 and 7.12 in C11/C17, to be precise). With -fexcess-precision=standard, gcc evaluates float in double precision, which aligns with the standard yet at the cost of added conversion instructions. To improve standards compliance, this patch changes the definition of float_t to be derived from the compiler's __FLT_EVAL_METHOD__. Note that glibc 2.33 will most likely adopt the same behavior on s390x. --- arch/s390x/bits/alltypes.h.in | 4 ++++ arch/s390x/bits/float.h | 6 +++++- 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/s390x/bits/alltypes.h.in b/arch/s390x/bits/alltypes.h.in index 15d18c8f..6c0eb7f4 100644 --- a/arch/s390x/bits/alltypes.h.in +++ b/arch/s390x/bits/alltypes.h.in @@ -9,7 +9,11 @@ TYPEDEF int wchar_t; #endif +#if defined(__FLT_EVAL_METHOD__) && __FLT_EVAL_METHOD__ == 1 TYPEDEF double float_t; +#else +TYPEDEF float float_t; +#endif TYPEDEF double double_t; TYPEDEF struct { long long __ll; long double __ld; } max_align_t; diff --git a/arch/s390x/bits/float.h b/arch/s390x/bits/float.h index 90b73bee..e188cb61 100644 --- a/arch/s390x/bits/float.h +++ b/arch/s390x/bits/float.h @@ -1,4 +1,8 @@ -#define FLT_EVAL_METHOD 1 +#ifdef __FLT_EVAL_METHOD__ +#define FLT_EVAL_METHOD __FLT_EVAL_METHOD__ +#else +#define FLT_EVAL_METHOD 0 +#endif #define LDBL_TRUE_MIN 6.47517511943802511092443895822764655e-4966L #define LDBL_MIN 3.36210314311209350626267781732175260e-4932L -- 2.26.2