# HG changeset patch
# User Armin Rigo <arigo@tunes.org>
# Date 1424942568 -3600
# Node ID c7edb1e84eb3c29cac0674790cb4efcbcf1683b2
# Parent  95e0563201602a2e1a8d83cc95a6a70048dfeece
issue #177: workaround for some Linux kernels

diff --git a/c/malloc_closure.h b/c/malloc_closure.h
--- a/c/malloc_closure.h
+++ b/c/malloc_closure.h
@@ -14,6 +14,54 @@
 # endif
 #endif
 
+/* On PaX enable kernels that have MPROTECT enable we can't use PROT_EXEC.
+
+   This is, apparently, an undocumented change to ffi_prep_closure():
+   depending on the Linux kernel we're running on, we must give it a
+   mmap that is either PROT_READ|PROT_WRITE|PROT_EXEC or only
+   PROT_READ|PROT_WRITE.  In the latter case, just trying to obtain a
+   mmap with PROT_READ|PROT_WRITE|PROT_EXEC would kill our process(!),
+   but in that situation libffi is fine with only PROT_READ|PROT_WRITE.
+   There is nothing in the libffi API to know that, though, so we have
+   to guess by parsing /proc/self/status.  "Meh."
+ */
+#ifdef __linux__
+#include <stdlib.h>
+
+static int emutramp_enabled = -1;
+
+static int
+emutramp_enabled_check (void)
+{
+    char *buf = NULL;
+    size_t len = 0;
+    FILE *f;
+    int ret;
+    f = fopen ("/proc/self/status", "r");
+    if (f == NULL)
+        return 0;
+    ret = 0;
+
+    while (getline (&buf, &len, f) != -1)
+        if (!strncmp (buf, "PaX:", 4))
+            {
+                char emutramp;
+                if (sscanf (buf, "%*s %*c%c", &emutramp) == 1)
+                    ret = (emutramp == 'E');
+                break;
+            }
+    free (buf);
+    fclose (f);
+    return ret;
+}
+
+#define is_emutramp_enabled() (emutramp_enabled >= 0 ? emutramp_enabled \
+        : (emutramp_enabled = emutramp_enabled_check ()))
+#else
+#define is_emutramp_enabled() 0
+#endif
+
+
 /* 'allocate_num_pages' is dynamically adjusted starting from one
    page.  It grows by a factor of PAGE_ALLOCATION_GROWTH_RATE.  This is
    meant to handle both the common case of not needing a lot of pages,
@@ -77,9 +125,12 @@
     if (item == NULL)
         return;
 #else
+    int prot = PROT_READ | PROT_WRITE | PROT_EXEC;
+    if (is_emutramp_enabled ())
+        prot &= ~PROT_EXEC;
     item = (union mmaped_block *)mmap(NULL,
                         allocate_num_pages * _pagesize,
-                        PROT_READ | PROT_WRITE | PROT_EXEC,
+                        prot,
                         MAP_PRIVATE | MAP_ANONYMOUS,
                         -1,
                         0);