From: Simon Scherer <[email protected]> helper_fcomi_ST0_FT0() and helper_fucomi_ST0_FT0() only cleared CC_Z, CC_P, and CC_C before merging in the comparison result, leaving CC_O, CC_S, and CC_A untouched from whatever they were set to beforehand.
The Intel SDM documents FCOMI/FCOMIP/FUCOMI/FUCOMIP as setting OF, SF, and AF to 0 unconditionally. The AMD manual doesn't mention them at all. However, testing on multiple real Intel and AMD systems confirms all three are unconditionally cleared regardless of the comparison result or their prior value. Since fcomi_ccval[] only ever contains CC_C, CC_Z, 0, or CC_Z|CC_P|CC_C, and CC_O|CC_S|CC_Z|CC_A|CC_P|CC_C already covers every flag bit, CC_SRC can be assigned from fcomi_ccval[ret + 1] directly instead of ORing it into a masked cpu_cc_compute_all() result. Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4133 Signed-off-by: Simon Scherer <[email protected]> Link: https://lore.kernel.org/r/[email protected] Cc: [email protected] Signed-off-by: Paolo Bonzini <[email protected]> (cherry picked from commit 0924d9d3db3617f49ba9282acc6d85b349404ce6) Signed-off-by: Michael Tokarev <[email protected]> diff --git a/target/i386/tcg/fpu_helper.c b/target/i386/tcg/fpu_helper.c index 56d456860fc..128f16dc951 100644 --- a/target/i386/tcg/fpu_helper.c +++ b/target/i386/tcg/fpu_helper.c @@ -550,12 +550,11 @@ static const int fcomi_ccval[4] = {CC_C, CC_Z, 0, CC_Z | CC_P | CC_C}; void helper_fcomi_ST0_FT0(CPUX86State *env) { int old_flags = save_exception_flags(env); - int eflags; FloatRelation ret; ret = floatx80_compare(ST0, FT0, &env->fp_status); - eflags = cpu_cc_compute_all(env) & ~(CC_Z | CC_P | CC_C); - CC_SRC = eflags | fcomi_ccval[ret + 1]; + /* OF, SF, and AF are unconditionally cleared to 0 */ + CC_SRC = fcomi_ccval[ret + 1]; CC_OP = CC_OP_EFLAGS; merge_exception_flags(env, old_flags); } @@ -563,12 +562,11 @@ void helper_fcomi_ST0_FT0(CPUX86State *env) void helper_fucomi_ST0_FT0(CPUX86State *env) { int old_flags = save_exception_flags(env); - int eflags; FloatRelation ret; ret = floatx80_compare_quiet(ST0, FT0, &env->fp_status); - eflags = cpu_cc_compute_all(env) & ~(CC_Z | CC_P | CC_C); - CC_SRC = eflags | fcomi_ccval[ret + 1]; + /* OF, SF, and AF are unconditionally cleared to 0 */ + CC_SRC = fcomi_ccval[ret + 1]; CC_OP = CC_OP_EFLAGS; merge_exception_flags(env, old_flags); } -- 2.47.3
