3 ms·

Please refrain from making things up -- Long Mode has always supported x87. You may be mis-remembering LAHF/SAHF.

• balou23 2mo ago
  LAHF and SAHF are an interesting rabbit hole themselves. If you ever dug into x86 assembler programming... at first they make no sense at all. They only save/restore a tiny part of the available flag registers. The mnemonics themselves make little sense - load/store are not really used in any other base x86 mnemonics (unlike e.g. 6502 mnemonics, which use LD?/ST? instead of MOV like x86). It only clicked when I read an Intel document about porting assembler code from the 8080 to the 8086. LAHF/SAHF are basically convenience instructions to make porting easier. Many 8080 instructions did not alter the flags, unlike their 8086 counterparts. Substituting an `INX` instruction with `LAHF; INC; SAHF` made it possible to mechanically translate assembler source code. And yeah, 8080 mnemonics had LDA and STA like the 6502...