🚀 go-pugleaf

There appears to be a bug in gcc's (2.2.2) handling of :0 bit fields when
specifying C++ as the language of choice. When the following program is
compiled for C it does what one would expect and positions structure member
'c' of structure 'foo' at an offset of 4 bytes from the beginning of the
structure. However, when the same program is compiled for C++ 'c' is
positioned at an offset of 8 bytes from the beginning of the structure,
apparently creating an "empty" word. As well, the C++ compilation
apparently rounds up the size of the structure to the nearest word, whereas
the C compilation does not. Note this is on a SPARC running SunOS 4.1.1.

******************* x.c *********************************************

#include <stdio.h>
#include <stddef.h>

struct foo {
	char a;
	char b;
	unsigned int : 0;	/* force word alignment */
	char c;
};	

int
main(int argc, char **argv)
{
	struct foo bar;

	printf("sizeof(bar) = %d\n", sizeof(bar));
	printf("offsetof b = %d; offsetof c = %d\n", offsetof(struct foo, b),
	        offsetof(struct foo, c));
	return(0);
}

******************* C compiled *********************************************

cd /tmp/
make -k x CFLAGS="-v -x c"
gcc -v -x c    x.c   -o x
Reading specs from /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/specs
gcc version 2.2.2
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/cpp -lang-c -v -undef -D__GNUC__=2 -Dsparc -Dsun -Dunix -D__sparc__ -D__sun__ -D__unix__ -D__sparc -D__sun -D__unix x.c /usr/tmp/cca16395.i
GNU CPP version 2.2.2 (sparc)
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/cc1 /usr/tmp/cca16395.i -quiet -dumpbase x.c -version -o /usr/tmp/cca16395.s
GNU C version 2.2.2 (sparc) compiled by GNU C version 2.2.2.
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/as -o x.o /usr/tmp/cca16395.s
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/ld -e start -dc -dp -o x /lib/crt0.o -L/van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2 -L/van/pdsw/lib.sun4 x.o -lgcc -lc -lgcc

------------- run it ------------
sun33k(2450) /tmp/x
sizeof(bar) = 5
offsetof b = 1; offsetof c = 4
sun33k(2451)

******************* C++ compiled *******************************************

cd /tmp/
make -k x CFLAGS="-v -x c++"
gcc -v -x c++    x.c   -o x
Reading specs from /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/specs
gcc version 2.2.2
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/cpp -lang-c++ -v -undef -D__GNUC__=2 -D__GNUG__=2 -D__cplusplus -Dsparc -Dsun -Dunix -D__sparc__ -D__sun__ -D__unix__ -D__sparc -D__sun -D__unix x.c /usr/tmp/cca16404.i
GNU CPP version 2.2.2 (sparc)
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/cc1plus /usr/tmp/cca16404.i -quiet -dumpbase x.cc -version -o /usr/tmp/cca16404.s
GNU C++ version 2.2.2 (sparc) compiled by GNU C version 2.2.2.
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/as -o x.o /usr/tmp/cca16404.s
 /van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2/ld -e start -dc -dp -o x /lib/crt0.o -L/van/pdsw/lib.sun4/gcc-lib/sparc-sun-sunos4.1/2.2.2 -L/van/pdsw/lib.sun4 x.o -lgcc -lc -lgcc

------------ run it -------------
sun33k(2452) /tmp/x
sizeof(bar) = 12
offsetof b = 1; offsetof c = 8
sun33k(2453)

****************************************************************
-- 
Jim Robinson
robinson@mdd.comm.mot.com
{ubc-cs!van-bc,uunet}!mdivax1!robinson