When building gdb with gcc-6.0.0-0.15.fc24 on s390x I'm getting "strict aliasing" warnings/errors. The warning/error doesn't appear when built with gcc-6.0.0-0.14.fc24. Filed against gdb to see whether it is a real bug before switching to gcc.


from build.log
...
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I../../bfd -DTRAD_CORE -I. -I../../bfd -I../../bfd/../include -DHAVE_s390_elf64_vec -DHAVE_s390_elf32_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_powerpc_elf32_vec -DHAVE_rs6000_xcoff_vec -DHAVE_powerpc_elf32_le_vec -DHAVE_powerpc_boot_vec -DHAVE_powerpc_elf64_vec -DHAVE_powerpc_elf64_le_vec -DHAVE_arm_elf32_le_vec -DHAVE_arm_elf32_be_vec -DHAVE_aarch64_elf64_le_vec -DHAVE_aarch64_elf64_be_vec -DHAVE_aarch64_elf32_le_vec -DHAVE_aarch64_elf32_be_vec -DHAVE_plugin_vec -DBINDIR=\"/usr/bin\" -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -march=z9-109 -mtune=z10 -DDNF_DEBUGINFO_INSTALL -DNEED_RL_STATE_FEDORA_GDB -MT coff-rs6000.lo -MD -MP -MF .deps/coff-rs6000.Tpo -c ../../bfd/coff-rs6000.c -o coff-rs6000.o
In file included from ../../bfd/coff-rs6000.c:118:0:
../../bfd/coffcode.h: In function 'coff_new_section_hook':
../../bfd/coffcode.h:1817:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   coffsymbol (section->symbol)->native = native;
   ^~~~~~~~~~
...
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I../../bfd -DTRAD_CORE -I. -I../../bfd -I../../bfd/../include -DHAVE_s390_elf64_vec -DHAVE_s390_elf32_vec -DHAVE_elf64_le_vec -DHAVE_elf64_be_vec -DHAVE_elf32_le_vec -DHAVE_elf32_be_vec -DHAVE_powerpc_elf32_vec -DHAVE_rs6000_xcoff_vec -DHAVE_powerpc_elf32_le_vec -DHAVE_powerpc_boot_vec -DHAVE_powerpc_elf64_vec -DHAVE_powerpc_elf64_le_vec -DHAVE_arm_elf32_le_vec -DHAVE_arm_elf32_be_vec -DHAVE_aarch64_elf64_le_vec -DHAVE_aarch64_elf64_be_vec -DHAVE_aarch64_elf32_le_vec -DHAVE_aarch64_elf32_be_vec -DHAVE_plugin_vec -DBINDIR=\"/usr/bin\" -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow -Werror -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -march=z9-109 -mtune=z10 -DDNF_DEBUGINFO_INSTALL -DNEED_RL_STATE_FEDORA_GDB -MT coffgen.lo -MD -MP -MF .deps/coffgen.Tpo -c ../../bfd/coffgen.c -o coffgen.o
../../bfd/coffgen.c: In function 'coff_get_lineno':
../../bfd/coffgen.c:1510:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   return coffsymbol (symbol)->lineno;
   ^~~~~~
../../bfd/coffgen.c: In function 'coff_get_symbol_info':
../../bfd/coffgen.c:2034:3: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   if (coffsymbol (symbol)->native != NULL
   ^~
../../bfd/coffgen.c:2035:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       && coffsymbol (symbol)->native->fix_value
       ^~
../../bfd/coffgen.c:2036:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       && coffsymbol (symbol)->native->is_sym)
       ^~
../../bfd/coffgen.c:2037:5: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
     ret->value = coffsymbol (symbol)->native->u.syment.n_value -
     ^~~
../../bfd/coffgen.c: In function 'coff_print_symbol':
../../bfd/coffgen.c:2059:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         coffsymbol (symbol)->native ? "n" : "g",
         ^~~~~~~~~~
../../bfd/coffgen.c:2060:9: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
         coffsymbol (symbol)->lineno ? "l" : " ");
         ^~~~~~~~~~
../../bfd/coffgen.c:2064:7: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
       if (coffsymbol (symbol)->native)
       ^~
../../bfd/coffgen.c:2068:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    combined_entry_type *combined = coffsymbol (symbol)->native;
    ^~~~~~~~~~~~~~~~~~~
../../bfd/coffgen.c:2070:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
    struct lineno_cache_entry *l = coffsymbol (symbol)->lineno;
           ^~~~~~~~~~~~~~~~~~
../../bfd/coffgen.c:2191:6: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
      coffsymbol (symbol)->native ? "n" : "g",
      ^~~~~~~~~~
../../bfd/coffgen.c:2192:6: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
      coffsymbol (symbol)->lineno ? "l" : " ",
      ^~~~~~~~~~
cc1: all warnings being treated as errors
...


For full logs from gdb-7.10.90.20160211-52.fc24 please see http://s390.koji.fedoraproject.org/koji/taskinfo?taskID=2139610 (-0.15 gcc used). For comparison see http://s390.koji.fedoraproject.org/koji/taskinfo?taskID=2140908 when -0.14 gcc is used (the only difference in the buildroot).


Version-Release number of selected component (if applicable):
gdb-7.11-58.fc24 (but also previous versions are affected)
gcc-6.0.0-0.15.fc24.s390x