On 14.07.2025 18:19, Andrew Cooper wrote: > On 14/07/2025 5:02 pm, Jan Beulich wrote: >> --- a/xen/arch/x86/x86_emulate/x86_emulate.c >> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c >> @@ -5270,62 +5270,26 @@ x86_emulate( >> break; >> >> case X86EMUL_OPC(0x0f, 0xbc): /* bsf or tzcnt */ >> - { >> - bool zf; >> - >> - asm ( "bsf %2,%0" ASM_FLAG_OUT(, "; setz %1") >> - : "=r" (dst.val), ASM_FLAG_OUT("=@ccz", "=qm") (zf) >> - : "rm" (src.val) ); >> - _regs.eflags &= ~X86_EFLAGS_ZF; >> - if ( (vex.pfx == vex_f3) && vcpu_has_bmi1() ) >> - { >> - _regs.eflags &= ~X86_EFLAGS_CF; >> - if ( zf ) >> - { >> - _regs.eflags |= X86_EFLAGS_CF; >> - dst.val = op_bytes * 8; >> - } >> - else if ( !dst.val ) >> - _regs.eflags |= X86_EFLAGS_ZF; >> - } >> - else if ( zf ) >> + if ( vex.pfx == vex_f3 ) >> + emulate_2op_SrcV_srcmem("rep; bsf", src, dst, _regs.eflags); > > Do we need the ; ? > > We surely don't on 4.21, but I presume there are bugs in older > binutils? (All Clangs back to 3.5 seem happy)
Actually we can use TZCNT here and LZCNT below with gas 2.25 (and Clang looks to be happy too, even version 3.0). I expect that's preferable over merely omitting the semicolons? Jan