Computing x86 ISA level at configure time
Florian Weimer
fweimer@redhat.com
Tue Apr 23 19:01:13 GMT 2024
I'm trying to build glibc with these configure arguments:
CC="gcc -march=x86-64-v3" CXX="g++ -march=x86-64-v3" \
--with-rtld-early-cflags=-march=x86-64
It does not quite work because the ld.so trampolines are now initialized
early, and at that point, -march=x86-64 is in effect. I tried to move
the computation to the configure state, so that it is frozen using the
default (not early) CC/CFLAGS combination. I've got a prototype patch,
but I've trouble understanding the meaning of “baseline” vs the other
options. Any suggestions how to proceed?
Thanks,
Florian
diff --git a/config.h.in b/config.h.in
index 69ac450356..602dd639eb 100644
--- a/config.h.in
+++ b/config.h.in
@@ -285,6 +285,9 @@
/* Define if x86 ISA level should be included in shared libraries. */
#undef INCLUDE_X86_ISA_LEVEL
+/* The x86-64 ISA level. 0 for baseline. Undefined on non-x86-64. */
+#undef MINIMUM_X86_ISA_LEVEL
+
/* Define if -msahf is enabled by default on x86. */
#undef HAVE_X86_LAHF_SAHF
diff --git a/sysdeps/x86/configure b/sysdeps/x86/configure
index 2a5421bb31..559adaa1c7 100644
--- a/sysdeps/x86/configure
+++ b/sysdeps/x86/configure
@@ -131,26 +131,61 @@ if test ${libc_cv_have_x86_isa_level+y}
then :
printf %s "(cached) " >&6
else $as_nop
- cat > conftest.c <<EOF
-#include <sysdeps/x86/isa-level.h>
-#if MINIMUM_X86_ISA_LEVEL >= 4
-libc_cv_have_x86_isa_level=4
-#elif MINIMUM_X86_ISA_LEVEL == 3
-libc_cv_have_x86_isa_level=3
-#elif MINIMUM_X86_ISA_LEVEL == 2
-libc_cv_have_x86_isa_level=2
+ cat > conftest.c <<'EOF'
+#if defined __SSE__ && defined __SSE2__
+/* NB: ISAs, excluding MMX, in x86-64 ISA level baseline are used. */
+# define __X86_ISA_V1 1
#else
-libc_cv_have_x86_isa_level=baseline
+# define __X86_ISA_V1 0
#endif
+
+#if __X86_ISA_V1 && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 \
+ && defined HAVE_X86_LAHF_SAHF && defined __POPCNT__ && defined __SSE3__ \
+ && defined __SSSE3__ && defined __SSE4_1__ && defined __SSE4_2__
+/* NB: ISAs in x86-64 ISA level v2 are used. */
+# define __X86_ISA_V2 1
+#else
+# define __X86_ISA_V2 0
+#endif
+
+#if __X86_ISA_V2 && defined __AVX__ && defined __AVX2__ && defined __F16C__ \
+ && defined __FMA__ && defined __LZCNT__ && defined HAVE_X86_MOVBE \
+ && defined __BMI__ && defined __BMI2__
+/* NB: ISAs in x86-64 ISA level v3 are used. */
+# define __X86_ISA_V3 1
+#else
+# define __X86_ISA_V3 0
+#endif
+
+#if __X86_ISA_V3 && defined __AVX512F__ && defined __AVX512BW__ \
+ && defined __AVX512CD__ && defined __AVX512DQ__ && defined __AVX512VL__
+/* NB: ISAs in x86-64 ISA level v4 are used. */
+# define __X86_ISA_V4 1
+#else
+# define __X86_ISA_V4 0
+#endif
+
+void
+emit_constant ()
+{
+ asm ("/* libc_cv_have_x86_isa_level=%c0 */"
+ :: "i" (__X86_ISA_V1 + __X86_ISA_V2 + __X86_ISA_V3 + __X86_ISA_V4));
+}
EOF
- eval `${CC-cc} $CFLAGS $CPPFLAGS $ISAFLAG -I$srcdir -E conftest.c | grep libc_cv_have_x86_isa_level`
+${CC-cc} $CFLAGS $CPPFLAGS $ISAFLAG -S -o- conftest.c | grep -o 'libc_cv_have_x86_isa_level=0-9'
+ eval `${CC-cc} $CFLAGS $CPPFLAGS $ISAFLAG -S -o- conftest.c | grep -o 'libc_cv_have_x86_isa_level=0-9'`
rm -rf conftest*
fi
{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_have_x86_isa_level" >&5
printf "%s\n" "$libc_cv_have_x86_isa_level" >&6; }
+ if test -z "$libc_cv_have_x86_isa_level" ; then
+ as_fn_error $? "Could not determine x86 ISA level" "$LINENO" 5
+ fi
else
- libc_cv_have_x86_isa_level=baseline
+ libc_cv_have_x86_isa_level=0
fi
+printf "%s\n" "#define MINIMUM_X86_ISA_LEVEL $libc_cv_have_x86_isa_level" >>confdefs.h
+
config_vars="$config_vars
have-x86-isa-level = $libc_cv_have_x86_isa_level"
config_vars="$config_vars
diff --git a/sysdeps/x86/configure.ac b/sysdeps/x86/configure.ac
index 78ff7c8f41..f9ba5f583e 100644
--- a/sysdeps/x86/configure.ac
+++ b/sysdeps/x86/configure.ac
@@ -88,23 +88,57 @@ if test $libc_cv_include_x86_isa_level = yes; then
# Check for ISA level support.
AC_CACHE_CHECK([for ISA level support],
libc_cv_have_x86_isa_level, [dnl
-cat > conftest.c <<EOF
-#include <sysdeps/x86/isa-level.h>
-#if MINIMUM_X86_ISA_LEVEL >= 4
-libc_cv_have_x86_isa_level=4
-#elif MINIMUM_X86_ISA_LEVEL == 3
-libc_cv_have_x86_isa_level=3
-#elif MINIMUM_X86_ISA_LEVEL == 2
-libc_cv_have_x86_isa_level=2
+cat > conftest.c <<'EOF'
+#if defined __SSE__ && defined __SSE2__
+/* NB: ISAs, excluding MMX, in x86-64 ISA level baseline are used. */
+# define __X86_ISA_V1 1
#else
-libc_cv_have_x86_isa_level=baseline
+# define __X86_ISA_V1 0
#endif
+
+#if __X86_ISA_V1 && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 \
+ && defined HAVE_X86_LAHF_SAHF && defined __POPCNT__ && defined __SSE3__ \
+ && defined __SSSE3__ && defined __SSE4_1__ && defined __SSE4_2__
+/* NB: ISAs in x86-64 ISA level v2 are used. */
+# define __X86_ISA_V2 1
+#else
+# define __X86_ISA_V2 0
+#endif
+
+#if __X86_ISA_V2 && defined __AVX__ && defined __AVX2__ && defined __F16C__ \
+ && defined __FMA__ && defined __LZCNT__ && defined HAVE_X86_MOVBE \
+ && defined __BMI__ && defined __BMI2__
+/* NB: ISAs in x86-64 ISA level v3 are used. */
+# define __X86_ISA_V3 1
+#else
+# define __X86_ISA_V3 0
+#endif
+
+#if __X86_ISA_V3 && defined __AVX512F__ && defined __AVX512BW__ \
+ && defined __AVX512CD__ && defined __AVX512DQ__ && defined __AVX512VL__
+/* NB: ISAs in x86-64 ISA level v4 are used. */
+# define __X86_ISA_V4 1
+#else
+# define __X86_ISA_V4 0
+#endif
+
+void
+emit_constant ()
+{
+ asm ("/* libc_cv_have_x86_isa_level=%c0 */"
+ :: "i" (__X86_ISA_V1 + __X86_ISA_V2 + __X86_ISA_V3 + __X86_ISA_V4));
+}
EOF
- eval `${CC-cc} $CFLAGS $CPPFLAGS $ISAFLAG -I$srcdir -E conftest.c | grep libc_cv_have_x86_isa_level`
+${CC-cc} $CFLAGS $CPPFLAGS $ISAFLAG -S -o- conftest.c | grep -o 'libc_cv_have_x86_isa_level=[0-9]'
+ eval `${CC-cc} $CFLAGS $CPPFLAGS $ISAFLAG -S -o- conftest.c | grep -o 'libc_cv_have_x86_isa_level=[0-9]'`
rm -rf conftest*])
+ if test -z "$libc_cv_have_x86_isa_level" ; then
+ AC_MSG_ERROR([Could not determine x86 ISA level])
+ fi
else
- libc_cv_have_x86_isa_level=baseline
+ libc_cv_have_x86_isa_level=0
fi
+AC_DEFINE_UNQUOTED([MINIMUM_X86_ISA_LEVEL], [$libc_cv_have_x86_isa_level])
LIBC_CONFIG_VAR([have-x86-isa-level], [$libc_cv_have_x86_isa_level])
LIBC_CONFIG_VAR([x86-isa-level-3-or-above], [3 4])
LIBC_CONFIG_VAR([enable-x86-isa-level], [$libc_cv_include_x86_isa_level])
diff --git a/sysdeps/x86/isa-level.h b/sysdeps/x86/isa-level.h
index 11fe1ca90c..c116ded2d8 100644
--- a/sysdeps/x86/isa-level.h
+++ b/sysdeps/x86/isa-level.h
@@ -28,42 +28,6 @@
#ifndef _ISA_LEVEL_H
#define _ISA_LEVEL_H
-#if defined __SSE__ && defined __SSE2__
-/* NB: ISAs, excluding MMX, in x86-64 ISA level baseline are used. */
-# define __X86_ISA_V1 1
-#else
-# define __X86_ISA_V1 0
-#endif
-
-#if __X86_ISA_V1 && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 \
- && defined HAVE_X86_LAHF_SAHF && defined __POPCNT__ && defined __SSE3__ \
- && defined __SSSE3__ && defined __SSE4_1__ && defined __SSE4_2__
-/* NB: ISAs in x86-64 ISA level v2 are used. */
-# define __X86_ISA_V2 1
-#else
-# define __X86_ISA_V2 0
-#endif
-
-#if __X86_ISA_V2 && defined __AVX__ && defined __AVX2__ && defined __F16C__ \
- && defined __FMA__ && defined __LZCNT__ && defined HAVE_X86_MOVBE \
- && defined __BMI__ && defined __BMI2__
-/* NB: ISAs in x86-64 ISA level v3 are used. */
-# define __X86_ISA_V3 1
-#else
-# define __X86_ISA_V3 0
-#endif
-
-#if __X86_ISA_V3 && defined __AVX512F__ && defined __AVX512BW__ \
- && defined __AVX512CD__ && defined __AVX512DQ__ && defined __AVX512VL__
-/* NB: ISAs in x86-64 ISA level v4 are used. */
-# define __X86_ISA_V4 1
-#else
-# define __X86_ISA_V4 0
-#endif
-
-#define MINIMUM_X86_ISA_LEVEL \
- (__X86_ISA_V1 + __X86_ISA_V2 + __X86_ISA_V3 + __X86_ISA_V4)
-
/* Depending on the minimum ISA level, a feature check result can be a
compile-time constant.. */
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