linux-user: fix bug about incorrect base addresss of gdt on i386 and x86_64

On linux user mode, CPUX86State::gdt::base from Different CPUX86State
Objects have same value, It is incorrect! Every CPUX86State::gdt::base
Must points to independent memory space.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1405
Signed-off-by: fanwenjie <fanwj@mail.ustc.edu.cn>
Message-Id: <4172b90.58b08.18631b77860.Coremail.fanwj@mail.ustc.edu.cn>
[lv: remove unnecessary casts, split overlong line]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/i386/cpu_loop.c

@@ -314,8 +314,17 @@ void cpu_loop(CPUX86State *env)
     }
 }
 
+static void target_cpu_free(void *obj)
+{
+    CPUArchState *env = ((CPUState *)obj)->env_ptr;
+    target_munmap(env->gdt.base, sizeof(uint64_t) * TARGET_GDT_ENTRIES);
+    g_free(obj);
+}
+
 void target_cpu_copy_regs(CPUArchState *env, struct target_pt_regs *regs)
 {
+    CPUState *cpu = env_cpu(env);
+    OBJECT(cpu)->free = target_cpu_free;
     env->cr[0] = CR0_PG_MASK | CR0_WP_MASK | CR0_PE_MASK;
     env->hflags |= HF_PE_MASK | HF_CPL_MASK;
     if (env->features[FEAT_1_EDX] & CPUID_SSE) {

linux-user/main.c

@@ -238,6 +238,14 @@ CPUArchState *cpu_copy(CPUArchState *env)
 
     new_cpu->tcg_cflags = cpu->tcg_cflags;
     memcpy(new_env, env, sizeof(CPUArchState));
+#if defined(TARGET_I386) || defined(TARGET_X86_64)
+    new_env->gdt.base = target_mmap(0, sizeof(uint64_t) * TARGET_GDT_ENTRIES,
+                                    PROT_READ | PROT_WRITE,
+                                    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    memcpy(g2h_untagged(new_env->gdt.base), g2h_untagged(env->gdt.base),
+           sizeof(uint64_t) * TARGET_GDT_ENTRIES);
+    OBJECT(new_cpu)->free = OBJECT(cpu)->free;
+#endif
 
     /* Clone all break/watchpoints.
        Note: Once we support ptrace with hw-debug register access, make sure