Add test for modifying code that was just run

mehfooz09 · May 27, 2018 · 2748b8a · 2748b8a
1 parent 75e8d35
commit 2748b8a
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Showing 3 changed files with 46 additions and 1 deletion.
diff --git a/tests/looper.c b/tests/looper.c
@@ -4,7 +4,7 @@
 #define nop() __asm__ volatile("")
 
 int main() {
-    int loops = 10000000;
+    int loops = 100000000;
     printf("looping %d times\n", loops);
     for (int i = 0; i < loops; i++)
         nop();

diff --git a/tests/meson.build b/tests/meson.build
@@ -21,6 +21,9 @@ executable('forkexec', ['forkexec.c'])
 
 executable('thread', ['thread.c'], dependencies: dependency('threads'))
 
+# various tests for code that modifies itself
+executable('modify', ['modify.c'], link_args: ['-zexecstack'])
+
 # qemu test program
 executable('qemu-test', ['qemu-test.c'], link_args: ['-lm'])
 

diff --git a/tests/modify.c b/tests/modify.c
@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <setjmp.h>
+#include <signal.h>
+
+static char code[] = {
+    0xb8, 0x01, 0x00, 0x00, 0x00, // movl $1, %eax
+    0xc3, // ret
+};
+
+static sigjmp_buf env;
+static int catching = 0;
+static void handle_segfault(int sig) {
+    if (catching) {
+        catching = 0;
+        siglongjmp(env, 1);
+    }
+}
+
+static void test(char *code, const char *name) {
+    printf("%-6s before: %d expected 1\n", name, ((int (*)()) code)());
+    code[1] = 2;
+    printf("%-6s after:  %d expected 2\n", name, ((int (*)()) code)());
+}
+
+int main() {
+    signal(SIGSEGV, handle_segfault);
+    void *code_copy = mmap(NULL, 0x1000, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
+    memcpy(code_copy, code, sizeof(code));
+
+    test(code, "static");
+    test(code_copy, "mmap");
+    munmap(code_copy, 0x1000);
+    printf("call nonexistent: ");
+    catching = 1;
+    if (!sigsetjmp(env, 1))
+        printf("%d expected segfault\n", ((int (*)()) code_copy)());
+    else
+        printf("segfault\n");
+    return 0;
+}