From Bugzilla Helper: User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0) Description of problem: The gcc with Linux 7.1 lays out long long bitfields in a way that is both incompatible with Linux 6.2, and just plain irrational. Surely, changing a field of type T to a bitfield of type T should not make a structure larger. A struct containing a char and a long long bitfield should occupy 12 bytes: 1 for the char, 3 for padding, and 8 for the long long. Version-Release number of selected component (if applicable): How reproducible: Always Steps to Reproduce: 1. Compile program as shown in "Additional Information". 2. Run program. Actual Results: sizeof(PlainField)=12 sizeof(BitField )=16 Expected Results: sizeof(PlainField)=12 sizeof(BitField )=12 Additional info: $ cat b.C #include <stdio.h> typedef long long T; struct PlainField { char c; T field; }; struct BitField { char c; T field: 61; }; int main() { printf("sizeof(PlainField)=%d\n", sizeof(PlainField)); printf("sizeof(BitField )=%d\n", sizeof(BitField)); return 0; } $ gcc -v b.C Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.96/specs gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-81) /usr/lib/gcc-lib/i386-redhat-linux/2.96/cpp0 -lang-c++ -D__GNUG__=2 - D__EXCEPTIONS -v -D__GNUC__=2 -D__GNUC_MINOR__=96 -D__GNUC_PATCHLEVEL__=0 - D__EL F__ -Dunix -Dlinux -D__ELF__ -D__unix__ -D__linux__ -D__unix -D__linux - Asystem(posix) -Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__ - D__tune _i386__ b.C /usr/tmp/ccbx3Oxo.ii GNU CPP version 2.96 20000731 (Red Hat Linux 7.1 2.96-81) (cpplib) (i386 Linux/ELF) ignoring nonexistent directory "/usr/local/include" ignoring nonexistent directory "/usr/i386-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/include/g++-3 /usr/lib/gcc-lib/i386-redhat-linux/2.96/include /usr/include End of search list. /usr/lib/gcc-lib/i386-redhat-linux/2.96/cc1plus /usr/tmp/ccbx3Oxo.ii - quiet -dumpbase b.C -version -o /usr/tmp/cckafkTF.s GNU C++ version 2.96 20000731 (Red Hat Linux 7.1 2.96-81) (i386-redhat- linux) compiled by GNU C version 2.96 20000731 (Red Hat Linux 7.1 2.96-81). as -V -Qy -o /usr/tmp/cc9K0tF0.o /usr/tmp/cckafkTF.s GNU assembler version 2.10.91 (i386-redhat-linux) using BFD version 2.10.91.0.2 /usr/lib/gcc-lib/i386-redhat-linux/2.96/collect2 -m elf_i386 -dynamic- linker /lib/ld-linux.so.2 /usr/lib/gcc-lib/i386-redhat- linux/2.96/../../../crt1 .o /usr/lib/gcc-lib/i386-redhat-linux/2.96/../../../crti.o /usr/lib/gcc- lib/i386-redhat-linux/2.96/crtbegin.o -L/usr/lib/gcc-lib/i386-redhat- linux/2.9 6 -L/usr/lib/gcc-lib/i386-redhat-linux/2.96/../../.. /usr/tmp/cc9K0tF0.o - lgcc -lc -lgcc /usr/lib/gcc-lib/i386-redhat- linux/2.96/crtend.o /usr/lib/gcc -lib/i386-redhat-linux/2.96/../../../crtn.o $ a.out sizeof(PlainField)=12 sizeof(BitField )=16 $
gcc 3.2 sorted all this out