https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85440
--- Comment #19 from Dennis Clarke <dclarke at blastwave dot org> ---
status : RESOLVED FIXED <-- seems to not apply.
For the sake of showing how there really is a problem here, we can
neatly compile some trivial code and get bizarre results simply
because the platform would prefer to use the non-standard IBM long
double data type. Any attempt to "add" two long doubles will result
in a call to _q_add which doesn't exist and ld fails.
ppc64$ cat foo.c
#define _XOPEN_SOURCE 600
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <locale.h>
#include <sys/utsname.h>
int main ( int argc, char *argv[] ) {
int j;
struct utsname uname_data;
long double pi = 3.14159265358979323846264338327950288419716939937510L;
long double one = 1.0L;
long double two = 2.0L;
setlocale( LC_MESSAGES, "C" );
if ( uname( &uname_data ) < 0 ) {
fprintf ( stderr,
"WARNING : Could not attain system uname data.\n" );
perror ( "uname" );
} else {
printf (" system name = %s\n", uname_data.sysname );
printf (" node name = %s\n", uname_data.nodename );
printf (" release = %s\n", uname_data.release );
printf (" version = %s\n", uname_data.version );
printf (" machine = %s\n", uname_data.machine );
}
printf ("\n");
/* correct 128 bit big endian hex representation of pi is
* 0x40 00 92 1f b5 44 42 d1 84 69 89 8c c5 17 01 b8 */
printf("\naddr \"pi\" is %p\n", &pi );
printf("\ncontents : " );
for ( j=0; j<sizeof(long double); j++ )
printf("%02x ", ((unsigned char *)&pi)[j] );
printf("\n" );
printf("%+42.38Lf\n", pi );
printf(" +3.1415926535897932384626433832795028841971 <- pi\n" );
printf("\n\naddr \"one\" is %p\n", &one );
printf("\ncontents : " );
for ( j=0; j<sizeof(long double); j++ )
printf("%02x ", ((unsigned char *)&one)[j] );
printf("\n" );
printf("%+42.38Lf\n", one );
printf("\n\naddr \"two\" is %p\n", &two );
printf("\ncontents : " );
for ( j=0; j<sizeof(long double); j++ )
printf("%02x ", ((unsigned char *)&two)[j] );
printf("\n" );
printf("%+42.38Lf\n", two );
return (EXIT_SUCCESS);
}
ppc64$
ppc64$ /usr/local/gcc7/bin/gcc -m64 -std=iso9899:2011 \
> -Wfatal-errors -pedantic-errors -mcpu=970 -mfull-toc \
> -mregnames -mabi=ieeelongdouble -o foo foo.c
gcc: warning: using IEEE extended precision long double
cc1: warning: using IEEE extended precision long double
ppc64$
ppc64$ ./foo
system name = Linux
node name = nix
release = 4.16.2-genunix
version = #1 SMP Wed Apr 18 16:41:48 GMT 2018
machine = ppc64
addr "pi" is 0x7fffe4399650
contents : 40 00 92 1f b5 44 42 d1 84 69 89 8c c5 17 01 b8
+2.07134954084936184770526779175270348787
+3.1415926535897932384626433832795028841971 <- pi
addr "one" is 0x7fffe4399660
contents : 3f ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+1.93750000000000000000000000000000000000
addr "two" is 0x7fffe4399670
contents : 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+2.00000000000000000000000000000000000000
ppc64$
ppc64$
ppc64$ /usr/local/gcc7/bin/gcc -m64 -std=iso9899:2011 \
> -Wfatal-errors -pedantic-errors -mcpu=970 -mfull-toc \
> -mregnames -mabi=ibmlongdouble -o foo foo.c
gcc: warning: using IBM extended precision long double
cc1: warning: using IBM extended precision long double
ppc64$ ./foo
system name = Linux
node name = nix
release = 4.16.2-genunix
version = #1 SMP Wed Apr 18 16:41:48 GMT 2018
machine = ppc64
addr "pi" is 0x7ffff5eef3e0
contents : 40 09 21 fb 54 44 2d 18 3c a1 a6 26 33 14 5c 06
+3.14159265358979323846264338327948122706
+3.1415926535897932384626433832795028841971 <- pi
addr "one" is 0x7ffff5eef3f0
contents : 3f f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+1.00000000000000000000000000000000000000
addr "two" is 0x7ffff5eef400
contents : 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+2.00000000000000000000000000000000000000
ppc64$
Like you say "...it doesn't work at all unless you provide your own library."
So very true.
Well this has been fun and I think a POWER9 server is needed to do
any real work and certainly the hardware support will be fun.
