Implement non-globally-atomic cmpxchg8b

saiminhtet · Jan 6, 2020 · 5f308a7 · 5f308a7
1 parent 8d005b1
commit 5f308a7
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diff --git a/emu/decode.h b/emu/decode.h
@@ -262,6 +262,12 @@ __no_instrument DECODER_RET glue(DECODER_NAME, OP_SIZE)(DECODER_ARGS) {
                 case 0xc1: TRACEI("xadd reg, modrm");
                            READMODRM; XADD(modrm_reg, modrm_val,oz); break;
 
+                case 0xc7: READMODRM_MEM; switch (modrm.opcode) {
+                               case 1: TRACEI("cmpxchg8b modrm");
+                                       CMPXCHG8B(modrm_val,64); break;
+                               default: UNDEFINED;
+                           };
+
 #if OP_SIZE != 16
                 case 0xc8: TRACEI("bswap eax");
                            BSWAP(reg_a); break;

diff --git a/jit/gadgets-aarch64/misc.S b/jit/gadgets-aarch64/misc.S
@@ -115,6 +115,32 @@
     gret 1
     write_bullshit 64, atomic_cmpxchg8b
 
+.gadget cmpxchg8b
+    write_prep 64, cmpxchg8b
+    mov w9, eax
+    bfi x9, xdx, 32, 32
+    mov w10, ebx
+    bfi x10, xcx, 32, 32
+
+    ldr x8, [_xaddr]
+    cmp x9, x8
+    csel x9, x8, x9, ne
+    csel x8, x10, x8, eq
+    cset w11, eq
+    str x8, [_xaddr]
+    write_done 64, cmpxchg8b
+    ubfx xax, x9, 0, 32
+    ubfx xdx, x9, 32, 32
+
+    ldr w8, [_cpu, CPU_flags_res]
+    ldr w9, [_cpu, CPU_eflags]
+    and w8, w8, ~ZF_RES
+    bfi w9, w11, 6, 1
+    str w8, [_cpu, CPU_flags_res]
+    str w9, [_cpu, CPU_eflags]
+    gret 1
+    write_bullshit 64, cmpxchg8b
+
 .macro do_helper type, size=
     .gadget helper_\type\size
         .ifin(\type, read,write)

diff --git a/jit/gadgets-x86_64/misc.S b/jit/gadgets-x86_64/misc.S
@@ -86,6 +86,17 @@
     orb %r15b, CPU_eflags(%_cpu)
     gret 1
 
+.gadget cmpxchg8b
+    write_prep 64, cmpxchg8b
+    cmpxchg8b (%_addrq)
+    setz %r15b
+    write_done 64, cmpxchg8b
+    andl $~ZF_RES, CPU_flags_res(%_cpu)
+    andl $~ZF_FLAG, CPU_eflags(%_cpu)
+    shlb $6, %r15b
+    orb %r15b, CPU_eflags(%_cpu)
+    gret 1
+
 .macro do_helper type, size=
     .gadget helper_\type\size
         .ifin(\type, read,write)

diff --git a/jit/gen.c b/jit/gen.c
@@ -340,6 +340,7 @@ static inline bool gen_op(struct gen_state *state, gadget_t *gadgets, enum arg a
 #define REPNZ(op, z) strop(op, repnz, z)
 
 #define CMPXCHG(src, dst,z) load(src, z); op(cmpxchg, dst, z)
+#define CMPXCHG8B(dst,z) g_addr(); gg(cmpxchg8b, saved_ip)
 #define XADD(src, dst,z) XCHG(src, dst,z); ADD(src, dst,z)
 
 void helper_rdtsc(struct cpu_state *cpu);