https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88307
Bug ID: 88307
Summary: lgammaq incorrectly sets signgam
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libquadmath
Assignee: unassigned at gcc dot gnu.org
Reporter: alex at webprise dot net
Target Milestone: ---
I know this is not in the libquadmath documentation but I see this (POSIX-like)
functionality in the source code.
Test case:
$ cat gamma.c
# define _GNU_SOURCE
# include <math.h>
# include <quadmath.h>
# include <stdio.h>
int main(void) {
printf("%d\n", signgam);
lgammaq(-.5q);
printf("%d\n", signgam);
lgamma(-.5);
printf("%d\n", signgam);
signgam = 0;
printf("%d\n", signgam);
lgammaq(-1.5q);
printf("%d\n", signgam);
lgamma(-1.5);
printf("%d\n", signgam);
return 0;
}
$ gcc -pedantic -std=c99 -Wno-pedantic gamma.c -l{m,quadmath} && ./a.out
0
1
-1
0
1
1
Expected result:
0
-1
-1
0
1
1
As we see, lgammaq sets signgam regardless of the sign of gamma function (here
negative at -.5 and positive -1.5). lgamma behaves as expected.
If, on the countrary, lgammaq is not intended to set signgam at all (and be
presumably thread-safe), then the bug should be formulated as: why lgammaq
touches signgam (whereas such behavior is not documented)?
Reporting for version 7.3.0 on Ubuntu 18.04 LTS (under WSL kernel):
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-16ubuntu3'
--with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --with-as=/usr/bin/x86_64-linux-gnu-as
--with-ld=/usr/bin/x86_64-linux-gnu-ld --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)
The same behavior is exhibited, e.g, on CentOS 6 with SCL:
$ scl enable devtoolset-7 -- gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,lto --prefix=/opt/rh/devtoolset-7/root/usr
--mandir=/opt/rh/devtoolset-7/root/usr/share/man
--infodir=/opt/rh/devtoolset-7/root/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-gcc-major-version-only --enable-plugin --with-linker-hash-style=gnu
--enable-initfini-array --with-default-libstdcxx-abi=gcc4-compatible
--with-isl=/builddir/build/BUILD/gcc-7.2.1-20170829/obj-x86_64-redhat-linux/isl-install
--enable-libmpx
--with-mpc=/builddir/build/BUILD/gcc-7.2.1-20170829/obj-x86_64-redhat-linux/mpc-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 7.2.1 20170829 (Red Hat 7.2.1-1) (GCC)
$ scl enable devtoolset-3 -- gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-3/root/usr/libexec/gcc/x86_64-redhat-linux/4.9.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/opt/rh/devtoolset-3/root/usr
--mandir=/opt/rh/devtoolset-3/root/usr/share/man
--infodir=/opt/rh/devtoolset-3/root/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap
--enable-shared --enable-threads=posix --enable-checking=release
--enable-multilib --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --enable-languages=c,c++,fortran,lto --enable-plugin
--with-linker-hash-style=gnu --enable-initfini-array --disable-libgcj
--with-isl=/builddir/build/BUILD/gcc-4.9.2-20150212/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.9.2-20150212/obj-x86_64-redhat-linux/cloog-install
--with-mpc=/builddir/build/BUILD/gcc-4.9.2-20150212/obj-x86_64-redhat-linux/mpc-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.9.2 20150212 (Red Hat 4.9.2-6) (GCC)
$ scl enable devtoolset-4 -- gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-4/root/usr/libexec/gcc/x86_64-redhat-linux/5.3.1/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,lto --prefix=/opt/rh/devtoolset-4/root/usr
--mandir=/opt/rh/devtoolset-4/root/usr/share/man
--infodir=/opt/rh/devtoolset-4/root/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id --enable-plugin
--with-linker-hash-style=gnu --enable-initfini-array --disable-libgcj
--with-default-libstdcxx-abi=gcc4-compatible
--with-isl=/builddir/build/BUILD/gcc-5.3.1-20160406/obj-x86_64-redhat-linux/isl-install
--enable-libmpx
--with-mpc=/builddir/build/BUILD/gcc-5.3.1-20160406/obj-x86_64-redhat-linux/mpc-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 5.3.1 20160406 (Red Hat 5.3.1-6) (GCC)
Compiler dry-run:
gcc -### -pedantic -std=c99 -Wno-pedantic gamma.c -l{m,quadmath}
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-16ubuntu3'
--with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --with-as=/usr/bin/x86_64-linux-gnu-as
--with-ld=/usr/bin/x86_64-linux-gnu-ld --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3)
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/7/cc1 -quiet -imultiarch x86_64-linux-gnu
gamma.c -quiet -dumpbase gamma.c "-mtune=generic" "-march=x86-64" -auxbase
gamma -Wno-pedantic "-std=c99" -fstack-protector-strong -Wformat
-Wformat-security -o /tmp/ccelUEuf.s
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
/usr/bin/x86_64-linux-gnu-as --64 -o /tmp/ccQUBs3O.o /tmp/ccelUEuf.s
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/7/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/7/liblto_plugin.so
"-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper"
"-plugin-opt=-fresolution=/tmp/ccAqCoDo.res" "-plugin-opt=-pass-through=-lgcc"
"-plugin-opt=-pass-through=-lgcc_s" "-plugin-opt=-pass-through=-lc"
"-plugin-opt=-pass-through=-lgcc" "-plugin-opt=-pass-through=-lgcc_s"
"--sysroot=/" --build-id --eh-frame-hdr -m elf_x86_64 "--hash-style=gnu"
--as-needed -dynamic-linker /lib64/ld-linux-x86-64.so.2 -pie -z now -z relro
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/7/crtbeginS.o -L/usr/lib/gcc/x86_64-linux-gnu/7
-L/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/7/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/7/../../.. /tmp/ccQUBs3O.o -lm -lquadmath -lgcc
--push-state --as-needed -lgcc_s --pop-state -lc -lgcc --push-state --as-needed
-lgcc_s --pop-state /usr/lib/gcc/x86_64-linux-gnu/7/crtendS.o
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
$ scl enable devtoolset-7 -- gcc -### -pedantic -std=c99 -Wno-pedantic gamma.c
-l{m,quadmath}
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,lto --prefix=/opt/rh/devtoolset-7/root/usr
--mandir=/opt/rh/devtoolset-7/root/usr/share/man
--infodir=/opt/rh/devtoolset-7/root/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-gcc-major-version-only --enable-plugin --with-linker-hash-style=gnu
--enable-initfini-array --with-default-libstdcxx-abi=gcc4-compatible
--with-isl=/builddir/build/BUILD/gcc-7.2.1-20170829/obj-x86_64-redhat-linux/isl-install
--enable-libmpx
--with-mpc=/builddir/build/BUILD/gcc-7.2.1-20170829/obj-x86_64-redhat-linux/mpc-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 7.2.1 20170829 (Red Hat 7.2.1-1) (GCC)
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/cc1 -quiet
gamma.c -quiet -dumpbase gamma.c "-mtune=generic" "-march=x86-64" -auxbase
gamma -Wno-pedantic "-std=c99" -o /tmp/cc9e853I.s
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/as --64 -o
/tmp/ccPiABQs.o /tmp/cc9e853I.s
COMPILER_PATH=/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/:/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/:/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/:/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/:/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/:/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/collect2
-plugin
/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/liblto_plugin.so
"-plugin-opt=/opt/rh/devtoolset-7/root/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper"
"-plugin-opt=-fresolution=/tmp/cc8eo9Cc.res" "-plugin-opt=-pass-through=-lgcc"
"-plugin-opt=-pass-through=-lgcc_s" "-plugin-opt=-pass-through=-lc"
"-plugin-opt=-pass-through=-lgcc" "-plugin-opt=-pass-through=-lgcc_s"
--build-id --no-add-needed --eh-frame-hdr "--hash-style=gnu" -m elf_x86_64
-dynamic-linker /lib64/ld-linux-x86-64.so.2 /usr/lib/../lib64/crt1.o
/usr/lib/../lib64/crti.o
/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o
-L/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7
-L/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64
-L/lib/../lib64 -L/usr/lib/../lib64
-L/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/../../..
/tmp/ccPiABQs.o -lm -lquadmath -lgcc --as-needed -lgcc_s --no-as-needed -lc
-lgcc --as-needed -lgcc_s --no-as-needed
/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/crtend.o
/usr/lib/../lib64/crtn.o
COLLECT_GCC_OPTIONS='-std=c99' '-Wno-pedantic' '-mtune=generic' '-march=x86-64'
Possible bug location:
Function __quadmath_lgamma_negq in lgammaq_neg.c.
