x86emul/test: factor out emul_test_make_stack_executable

It will be used by emulator fuzzing target.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

tools/tests/x86_emulator/test_x86_emulator.c

@@ -23,8 +23,6 @@ static const struct {
 #endif
 };
 
-#define MMAP_SZ 16384
-
 /* EFLAGS bit definitions. */
 #define EFLG_OF (1<<11)
 #define EFLG_DF (1<<10)
@@ -234,7 +232,6 @@ int main(int argc, char **argv)
     struct cpu_user_regs regs;
     char *instr;
     unsigned int *res, i, j;
-    unsigned long sp;
     bool stack_exec;
     int rc;
 #ifndef __x86_64__
@@ -258,13 +255,8 @@ int main(int argc, char **argv)
     }
     instr = (char *)res + 0x100;
 
-#ifdef __x86_64__
-    asm ("movq %%rsp, %0" : "=g" (sp));
-#else
-    asm ("movl %%esp, %0" : "=g" (sp));
-#endif
-    stack_exec = mprotect((void *)(sp & -0x1000L) - (MMAP_SZ - 0x1000),
-                          MMAP_SZ, PROT_READ|PROT_WRITE|PROT_EXEC) == 0;
+    stack_exec = emul_test_make_stack_executable();
+
     if ( !stack_exec )
         printf("Warning: Stack could not be made executable (%d).\n", errno);
 

tools/tests/x86_emulator/x86_emulate.c

@@ -1,5 +1,7 @@
 #include "x86_emulate.h"
 
+#include <sys/mman.h>
+
 #define EFER_SCE       (1 << 0)
 #define EFER_LMA       (1 << 10)
 
@@ -18,4 +20,22 @@
 #define get_stub(stb) ((void *)((stb).addr = (uintptr_t)(stb).buf))
 #define put_stub(stb)
 
+bool emul_test_make_stack_executable(void)
+{
+    unsigned long sp;
+
+    /*
+     * Mark the entire stack executable so that the stub executions
+     * don't fault
+     */
+#ifdef __x86_64__
+    asm ("movq %%rsp, %0" : "=g" (sp));
+#else
+    asm ("movl %%esp, %0" : "=g" (sp));
+#endif
+
+    return mprotect((void *)(sp & -0x1000L) - (MMAP_SZ - 0x1000),
+                    MMAP_SZ, PROT_READ|PROT_WRITE|PROT_EXEC) == 0;
+}
+
 #include "x86_emulate/x86_emulate.c"

tools/tests/x86_emulator/x86_emulate.h

@@ -33,4 +33,7 @@
 
 #define is_canonical_address(x) (((int64_t)(x) >> 47) == ((int64_t)(x) >> 63))
 
+#define MMAP_SZ 16384
+bool emul_test_make_stack_executable(void);
+
 #include "x86_emulate/x86_emulate.h"