[PATCH v2 09/13] x86/kvm/emulate: Convert em_salc() to C

Peter Zijlstra
2025-04-30T11:26:46Z

Implement the SALC (Set AL if Carry) instruction in C.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kvm/emulate.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -529,11 +529,14 @@ static int fastop(struct x86_emulate_ctx
ON64(FOP3E(op##q, rax, rdx, cl)) \
FOP_END

-FOP_START(salc)
-FOP_FUNC(salc)
-"pushf; sbb %al, %al; popf \n\t"
-FOP_RET(salc)
-FOP_END;
+static int em_salc(struct x86_emulate_ctxt *ctxt)
+{
+ /*
+ * Set AL 0xFF if CF is set, or 0x00 when clear.
+ */
+ ctxt->dst.val = 0xFF * !!(ctxt->eflags & X86_EFLAGS_CF);
+ return X86EMUL_CONTINUE;
+}

/*
* XXX: inoutclob user must know where the argument is being expanded.
@@ -4423,7 +4426,7 @@ static const struct opcode opcode_table[
G(Src2CL | ByteOp, group2), G(Src2CL, group2),
I(DstAcc | SrcImmUByte | No64, em_aam),
I(DstAcc | SrcImmUByte | No64, em_aad),
- F(DstAcc | ByteOp | No64, em_salc),
+ I(DstAcc | ByteOp | No64, em_salc),
I(DstAcc | SrcXLat | ByteOp, em_mov),
/* 0xD8 - 0xDF */
N, E(0, &escape_d9), N, E(0, &escape_db), N, E(0, &escape_dd), N, N,