Stack address size on 80486, using gcc

GCC manual says that -m32"generates code that runs on any i386 system". Assume I want to write a function that swaps the bytes of a 32 bit number:

    .text    .globl  SwapBytes    .type   SwapBytes, @functionSwapBytes:    pushl %ebp    movl %esp, %ebp    movl 8(%ebp), %eax    bswapl %eax    popl %ebp    ret

However, the BSWAP instruction is not supported on 80386, only since 80486. So I assemble gcc SwapBytes.s -march=i486 -c -o SwapBytes.elf, as suggested by the cited manual. But then I get an error:

Assembler messages:Error: invalid instruction suffix for `push'Error: invalid instruction suffix for `pop'

But why? I thought, 32 bit stack was introduced with 80386. Ok, let's try with -march=pentium3 in case I missed something about 32 bit stack, but the same result. However, if I assemble just with the -m32 option, gcc does not complain.

I thought maybe gcc ignores the -march=... options when assembling (and assumes -m64?), but does not ignore the -m32 option? But what options can I use to specify the CPU I want to assemble for?