Print backtrace on failed ASSERT_PKRU

Author: ayrtonm

runtime/libia2/ia2.c

@@ -1,6 +1,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #endif
+#include <execinfo.h>
 #include <inttypes.h>
 #include <stdio.h>
 #include <string.h>
@@ -497,3 +498,21 @@ int protect_pages(struct dl_phdr_info *info, size_t size, void *data) {
   // library
   return 0;
 }
+
+#if IA2_DEBUG
+void ia2_print_backtrace(void) {
+#define IA2_BT_SZ 10
+    void *ra_buf[IA2_BT_SZ];
+    int num_ra = backtrace(ra_buf, IA2_BT_SZ);
+    char **fn_names = backtrace_symbols(ra_buf, num_ra);
+    for (size_t i = 0; i < num_ra; i++) {
+        if (fn_names) {
+            fprintf(stderr, "#%d %p in %s ()\n", i, ra_buf[i], fn_names[i]);
+        } else {
+            fprintf(stderr, "#%d %p ()\n", i, ra_buf[i]);
+        }
+    }
+    fflush(stderr);
+    _exit(-1);
+}
+#endif

runtime/libia2/include/ia2.h

@@ -102,7 +102,12 @@
   "rdpkru\n"                                    \
   "cmpl $" #pkru ", %eax\n"                     \
   "je 1f\n"                                     \
-  "ud2\n"                                       \
+  "movq %rax, %rax\n"                           \
+  "movq %rcx, %rcx\n"                           \
+  "movq %rdx, %rdx\n"                           \
+  "wrpkru\n"                                    \
+  "subq $8, %rsp\n"                             \
+  "call ia2_print_backtrace\n"                  \
 "1:\n"                                          \
   "movq %r11, %rdx\n"                           \
   "movq %r10, %rcx\n"
@@ -157,6 +162,10 @@ uint32_t ia2_get_pkru();
 /// Returns the current compartment pkey
 size_t ia2_get_pkey();
 
+#if IA2_DEBUG
+void ia2_print_backtrace(void);
+#endif
+
 #ifdef __cplusplus
 }
 #endif