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[Qemu-devel] [PULL 02/20] target/i386: Fix andn instruction

From: Paolo Bonzini
Subject: [Qemu-devel] [PULL 02/20] target/i386: Fix andn instruction
Date: Fri, 6 Apr 2018 19:11:03 +0200

From: Alexandro Sanchez Bach <address@hidden>

In commit 7073fbada733c8d10992f00772c9b9299d740e9b, the `andn` instruction
was implemented via `tcg_gen_andc` but passes the operands in the wrong
- X86 defines `andn dest,src1,src2` as: dest = ~src1 & src2
- TCG defines `andc dest,src1,src2` as: dest = src1 & ~src2

The following simple test shows the issue:

    #include <stdio.h>
    #include <stdint.h>

    int main(void) {
        uint32_t ret = 0;
        __asm (
            "mov $0xFF00, %%ecx\n"
            "mov $0x0F0F, %%eax\n"
            "andn %%ecx, %%eax, %%ecx\n"
            "mov %%ecx, %0\n"
          : "=r" (ret));
        printf("%08X\n", ret);
        return 0;

This patch fixes the problem by simply swapping the order of the two last
arguments in `tcg_gen_andc_tl`.

Reported-by: Alexandro Sanchez Bach <address@hidden>
Signed-off-by: Alexandro Sanchez Bach <address@hidden>
Cc: address@hidden
Signed-off-by: Paolo Bonzini <address@hidden>
 target/i386/translate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/i386/translate.c b/target/i386/translate.c
index 0135415..3b7ce92 100644
--- a/target/i386/translate.c
+++ b/target/i386/translate.c
@@ -3802,7 +3802,7 @@ static void gen_sse(CPUX86State *env, DisasContext *s, 
int b,
                 ot = mo_64_32(s->dflag);
                 gen_ldst_modrm(env, s, modrm, ot, OR_TMP0, 0);
-                tcg_gen_andc_tl(cpu_T0, cpu_regs[s->vex_v], cpu_T0);
+                tcg_gen_andc_tl(cpu_T0, cpu_T0, cpu_regs[s->vex_v]);
                 gen_op_mov_reg_v(ot, reg, cpu_T0);
                 set_cc_op(s, CC_OP_LOGICB + ot);

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