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A comment on Show HN: A simple way to write standalone C programs for i386. Parent comment

Re:Show HN: A simple way to write standalone C programs for ... by rwmj on Wednesday October 02, 2019 @08:45AM (#21135759)
No, he's using -m16 -march=i386 which creates 32 bit code that boots in 16 bit mode using the 32 bit size prefix on most instructions, and that will only work on 80386 and above.
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Re:Show HN: A simple way to write standalone C programs for ... by jacobush on Wednesday October 02, 2019 @10:29AM (#21136822)
This is so insane, I had no idea such a thing was possible:

16 vs 32 bit It is possible to use 32-bit instructions in the real-address mode, they just need to be marked with address-size and operand-size prefixes. The -m16 option for clang/gcc, and .code16 directive in GNU assembler, do exactly that. The resulting code is 32-bit, only marked everywhere with those prefixes. It's not compatible with actual 16-bit CPUs.

"Unfortunately the 32-bit addresses still cannot exceed the boundary of the segment (65535), otherwise they'll trigger an exception. QEMU doesn't emulate this behaviour, so it's useful to occasionally test with Bochs."

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