Re: Natural alignment used on NetBSD/m68k

[Chris Hanson <cmhanson%eschatologist.net@localhost>]

Having been a Mac developer way back when, I know a lot of older 68K platforms used two-byte alignment; it doesn’t surprise me that NetBSD a.out would use it too. I suspect the same is true of SunOS; unfortunately I’m not in a position to power up my Sun-3/60C at the moment to check what SunOS 4.1.1_U1 uses. If someone has SunOS running in TME then it should be straightforward to get this information though.

  -- Chris

> On Feb 8, 2025, at 1:23 PM, Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost> wrote:
> 
>>> Maybe we have to clarify the definition of "a natural alignment",
>>> but IIRC there were incompatible alignment issue when we have
>>> switched from a.out to ELF.
>> 
>> Yes, it was always this way since we switched to ELF.
> 
> For clarification:
> 
> ---
> 
> x68030-% uname -a
> NetBSD x68030 1.5.3 NetBSD 1.5.3 (GENERIC) #5: Wed Jul  3 13:29:05 JST 2002     nsmrtks%yellow.magic.or@localhost:/lhd/src-1-5-PATCH003/sys/arch/x68k/compile/GENERIC x68k
> x68030-% gcc -v
> Using builtin specs.
> gcc version egcs-2.91.66 19990314 (egcs-1.1.2 release)
> x68030-% cat > test.c
> #include <stdio.h>
> #include <stddef.h>
> 
> struct test { char x; int y; };
> typedef struct test test_t;
> 
> int main(void)
> {
>    printf("struct test { char x; int y; };\n");
>    printf("sizeof(struct test) = %d\n", sizeof(struct test));
>    printf("offsetof(struct test, y) = %d\n", offsetof(struct test, y));
> }
> x68030-% cc test.c
> x68030-% file a.out
> a.out: NetBSD/m68k demand paged dynamically linked executable not stripped
> x68030-% ./a.out
> struct test { char x; int y; };
> sizeof(struct test) = 6
> offsetof(struct test, y) = 2
> x68030-% 
> 
> ---
> 
> milan-% uname -a
> NetBSD milan 10.1 NetBSD 10.1 (MILAN-PCIIDE) #0: Mon Dec 16 13:08:11 UTC 2024  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/atari/compile/MILAN-PCIIDE atari
> milan-% gcc -v
> Using built-in specs.
> COLLECT_GCC=gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/lto-wrapper
> Target: m68k--netbsdelf
> Configured with: /usr/src/tools/gcc/../../external/gpl3/gcc/dist/configure --target=m68k--netbsdelf --enable-long-long --enable-threads --with-bugurl=http://www.NetBSD.org/support/send-pr.html --with-pkgversion='NetBSD nb2 20230710' --with-system-zlib --without-isl --enable-__cxa_atexit --enable-libstdcxx-time=rt --enable-libstdcxx-threads --with-diagnostics-color=auto-if-env --with-default-libstdcxx-abi=new --with-mpc-lib=/var/obj/mknative/mvme68k-m68k/usr/src/external/lgpl3/mpc/lib/libmpc --with-mpfr-lib=/var/obj/mknative/mvme68k-m68k/usr/src/external/lgpl3/mpfr/lib/libmpfr --with-gmp-lib=/var/obj/mknative/mvme68k-m68k/usr/src/external/lgpl3/gmp/lib/libgmp --with-mpc-include=/usr/src/external/lgpl3/mpc/dist/src --with-mpfr-include=/usr/src/external/lgpl3/mpfr/dist/src --with-gmp-include=/usr/src/external/lgpl3/gmp/lib/libgmp/arch/m68k --enable-tls --disable-multilib --disable-libstdcxx-pch --build=m68k--netbsdelf --host=m68k--netbsdelf --with-sysroot=/var/obj/mknative/mvme!
> 68k-m68k/usr/src/destdir.mvme68k
> Thread model: posix
> Supported LTO compression algorithms: zlib
> gcc version 10.5.0 (nb3 20231008) 
> milan-% cat > test.c
> #include <stdio.h>
> #include <stddef.h>
> 
> struct test { char x; int y; };
> typedef struct test test_t;
> 
> int main(void)
> {
>    printf("struct test { char x; int y; };\n");
>    printf("sizeof(struct test) = %d\n", sizeof(struct test));
>    printf("offsetof(struct test, y) = %d\n", offsetof(struct test, y));
> }
> milan-% cc test.c
> milan-% file a.out
> a.out: ELF 32-bit MSB executable, Motorola m68k, 68020, version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld.elf_so, for NetBSD 10.1, with debug_info, not stripped
> milan-% ./a.out
> struct test { char x; int y; };
> sizeof(struct test) = 8
> offsetof(struct test, y) = 4
> milan-% 
> 
> ---
> Izumi Tsutsui
>