orccompiler: Implement checking for JIT support under Linux

This enables falling back to emulation when mmap(2) is not available
for executable pages. This seems to be the case under a combination
of SELinux sandboxing and noexec mounting.

Part-of: <https://gitlab.freedesktop.org/gstreamer/orc/-/merge_requests/176>

3 files changed, 29 insertions, 10 deletions

diff --git a/orc/orccodemem.c b/orc/orccodemem.c
index e128d0d..c59c77e 100644
--- a/orc/orccodemem.c
+++ b/orc/orccodemem.c
@@ -37,8 +37,6 @@
 /* See _orc_compiler_init() */
 extern int _orc_codemem_alignment;
 
-typedef struct _OrcCodeRegion OrcCodeRegion;
-
 struct _OrcCodeRegion {
   orc_uint8 *write_ptr;
   orc_uint8 *exec_ptr;
diff --git a/orc/orccompiler.c b/orc/orccompiler.c
index 7591858..b3e29e0 100644
--- a/orc/orccompiler.c
+++ b/orc/orccompiler.c
@@ -112,16 +112,18 @@ _orc_compiler_init (void)
   _orc_codemem_alignment = 15;
 #endif
 
-#ifdef ORC_WINAPI_ONLY_APP
-  if (!_orc_compiler_flag_backup && !_orc_compiler_flag_emulate) {
-    int can_jit = FALSE;
+  int can_jit = TRUE;
 
+  if (!_orc_compiler_flag_backup && !_orc_compiler_flag_emulate) {
     /* If backup code is not enabled and emulation is not enabled, that means
      * we will do JIT compilation and call orc_code_region_allocate_codemem().
-     * When targeting Windows Store apps, the codeGeneration capability must
+     */
+#if defined(HAVE_CODEMEM_VIRTUALALLOC) && defined(ORC_WINAPI_ONLY_APP)
+    /* When targeting Windows Store apps, the codeGeneration capability must
      * be enabled in the app manifest, or passing PAGE_EXECUTE to
      * VirtualProtectFromApp will return NULL. In this case, we must force
      * backup C code, and if that's not available, we must emulate. */
+    can_jit = FALSE;
     void *mem = VirtualAllocFromApp (NULL, page_size, MEM_COMMIT,
         PAGE_READWRITE);
     if (mem) {
@@ -129,16 +131,32 @@ _orc_compiler_init (void)
       if (VirtualProtectFromApp (mem, page_size, PAGE_EXECUTE, &old_protect) > 0)
         can_jit = TRUE;
       VirtualFree (mem, 0, MEM_RELEASE);
+    } else {
+      ORC_WARNING ("Unable to allocate executable pages: using backup code or "
+        "emulation: codeGeneration capability isn't set in the app manifest?");
     }
+#elif defined(HAVE_CODEMEM_MMAP)
+    /* In this case, we need to check that we can mmap pages as executable.
+     * This is not the case under the combination of SELinux and sandboxing
+     * profiles.
+     */
+    can_jit = FALSE;
+    OrcCodeRegion *region = orc_code_region_alloc();
+    if (region) {
+      can_jit = TRUE;
+      // FIXME: the file descriptor should be kept somewhere
+      // Currently the underlying mmap'd pages are leaked
+      free(region);
+    } else {
+      ORC_WARNING ("Unable to allocate executable pages: using backup code or emulation");
+    }
+#endif
 
     if (!can_jit) {
-      ORC_WARNING ("Unable to allocate executable pages: using backup code or "
-        "emulation: codeGeneration capability isn't set in the app manifest?");
       _orc_compiler_flag_backup = TRUE;
       _orc_compiler_flag_emulate = TRUE;
     }
   }
-#endif
 }
 
 int
diff --git a/orc/orcinternal.h b/orc/orcinternal.h
index d1355a0..f7374a4 100644
--- a/orc/orcinternal.h
+++ b/orc/orcinternal.h
@@ -21,9 +21,12 @@ void orc_c64x_init (void);
 void orc_c64x_c_init (void);
 void orc_mips_init (void);
 
+typedef struct _OrcCodeRegion OrcCodeRegion;
 typedef struct _OrcCodeChunk OrcCodeChunk;
 
-/* This is internal API, nothing in the public headers returns an OrcCodeChunk */
+/* This is internal API, nothing in the public headers returns an OrcCodeChunk
+ */
+OrcCodeRegion * orc_code_region_alloc (void);
 void orc_code_chunk_free (OrcCodeChunk *chunk);
 
 extern int _orc_data_cache_size_level1;