[libpng15] Use approved/supported Android method to check for NEON, use Linux/POSIX

1003.1 API to check /proc/self/auxv avoiding buffer allocation and other
library calls.

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.5.15beta05 - February 15, 2013
+Libpng 1.5.15beta05 - February 16, 2013
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -49,7 +49,10 @@ Version 1.5.15beta04 [February 15, 2013]
   Enclosed the new png_get_palette_max in #ifdef PNG_GET_PALETTE_MAX_SUPPORTED
     block, and revised pnglibconf.h and pnglibconf.h.prebuilt accordingly.
 
-Version 1.5.15beta05 [February 15, 2013]
+Version 1.5.15beta05 [February 16, 2013]
+  Use approved/supported Android method to check for NEON, use Linux/POSIX
+    1003.1 API to check /proc/self/auxv avoiding buffer allocation and other
+    library calls.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

CHANGES

@@ -4006,7 +4006,10 @@ Version 1.5.15beta04 [February 15, 2013]
   Enclosed the new png_get_palette_max in #ifdef PNG_GET_PALETTE_MAX_SUPPORTED
     block, and revised pnglibconf.h and pnglibconf.h.prebuilt accordingly.
 
-Version 1.5.15beta05 [February 15, 2013]
+Version 1.5.15beta05 [February 16, 2013]
+  Use approved/supported Android method to check for NEON, use Linux/POSIX
+    1003.1 API to check /proc/self/auxv avoiding buffer allocation and other
+    library calls.
 
   ===========================================================================
                        NOTICE November 17, 2012:

arm/arm_init.c

@@ -9,45 +9,154 @@
  * For conditions of distribution and use, see the disclaimer
  * and license in png.h
  */
+/* Below, after checking __linux__, various non-C90 POSIX 1003.1 functions are
+ * called.
+ */
+#define _POSIX_SOURCE 1
+
 #include "../pngpriv.h"
 
-/* __arm__ is defined by GCC, MSVC defines _M_ARM to the ARM version number */
+/* __arm__ is defined by GCC, MSVC defines _M_ARM to the ARM version number,
+ * Andoid intends to define __ANDROID__, however there are bugs in their
+ * toolchain; use -D__ANDROID__ to work round this.
+ */
 #if defined __linux__ && defined __arm__
-#include <stdio.h>
+#define CHECK_NEON
+#include <signal.h> /* for sig_atomic_t */
+
+#ifdef __ANDROID__
+/* Linux provides access to information about CPU capabilites via
+ * /proc/self/auxv, however Android blocks this while still claiming to be
+ * Linux.  The Andoid NDK, however, provides appropriate support.
+ *
+ * Documentation: http://www.kandroid.org/ndk/docs/CPU-ARM-NEON.html
+ */
+#include <cpu-features.h>
+
+static int
+png_have_neon(png_structp png_ptr)
+{
+   /* This is a whole lot easier than the mess below, however it is probably
+    * implemented as below, therefore it is better to cache the result (these
+    * function calls may be slow!)
+    */
+   return andoid_getCpuFamily() == ANDROID_CPU_FAMILY_ARM &&
+      (android_getCpuFeatures() & ANDROID_CPU_ARM_FEATURE_NEON) != 0;
+}
+#else
+/* The generic __linux__ implementation requires reading /proc/self/auxv and
+ * looking at each element for one that records NEON capabilities.
+ */
+#include <unistd.h> /* for POSIX 1003.1 */
+#include <errno.h>  /* for EINTR */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include <elf.h>
 #include <asm/hwcap.h>
 
-static int png_have_hwcap(unsigned cap)
+/* A read call may be interupted, in which case it returns -1 and sets errno to
+ * EINTR if nothing was done, otherwise (if something was done) a partial read
+ * may result.
+ */
+static size_t
+safe_read(png_structp png_ptr, int fd, void *buffer_in, size_t nbytes)
 {
-   FILE *f = fopen("/proc/self/auxv", "r");
-   Elf32_auxv_t aux;
-   int have_cap = 0;
+   size_t ntotal = 0;
+   char *buffer = png_voidcast(char*, buffer_in);
 
-   if (!f)
-      return 0;
-
-   while (fread(&aux, sizeof(aux), 1, f) > 0)
+   while (nbytes > 0)
    {
-      if (aux.a_type == AT_HWCAP &&
-          aux.a_un.a_val & cap)
+      unsigned int nread;
+      int iread;
+
+      /* Passing nread > INT_MAX to read is implementation defined in POSIX
+       * 1003.1, therefore despite the unsigned argument portable code must
+       * limit the value to INT_MAX!
+       */
+      if (nbytes > INT_MAX)
+         nread = INT_MAX;
+
+      else
+         nread = (unsigned int)/*SAFE*/nbytes;
+
+      iread = read(fd, buffer, nread);
+
+      if (iread == -1)
       {
-         have_cap = 1;
-         break;
+         /* This is the devil in the details, a read can terminate early with 0
+          * bytes read because of EINTR, yet it still returns -1 otherwise end
+          * of file cannot be distinguished.
+          */
+         if (errno != EINTR)
+         {
+            png_warning(png_ptr, "/proc read failed");
+            return 0; /* I.e. a permanent failure */
+         }
+      }
+
+      else if (iread < 0)
+      {
+         /* Not a valid 'read' result: */
+         png_warning(png_ptr, "OS /proc read bug");
+         return 0;
+      }
+
+      else if (iread > 0)
+      {
+         /* Continue reading until a permanent failure, or EOF */
+         buffer += iread;
+         nbytes -= (unsigned int)/*SAFE*/iread;
+         ntotal += (unsigned int)/*SAFE*/iread;
+      }
+
+      else
+         return ntotal;
+   }
+
+   return ntotal; /* nbytes == 0 */
+}
+
+static int
+png_have_neon(png_structp png_ptr)
+{
+   int fd = open("/proc/self/auxv", O_RDONLY);
+   Elf32_auxv_t aux;
+
+   /* Failsafe: failure to open means no NEON */
+   if (fd == -1)
+   {
+      png_warning(png_ptr, "/proc/self/auxv open failed");
+      return 0;
+   }
+
+   while (safe_read(png_ptr, fd, &aux, sizeof aux) == sizeof aux)
+   {
+      if (aux.a_type == AT_HWCAP && (aux.a_un.a_val & HWCAP_NEON) != 0)
+      {
+         close(fd);
+         return 1;
       }
    }
 
-   fclose(f);
-
-   return have_cap;
+   close(fd);
+   return 0;
 }
+#endif /* !__ANDROID__ */
 #endif /* __linux__ && __arm__ */
 
 void
 png_init_filter_functions_neon(png_structp pp, unsigned int bpp)
 {
 #ifdef __arm__
-#ifdef __linux__
-   if (!png_have_hwcap(HWCAP_NEON))
+#ifdef CHECK_NEON
+   static volatile sig_atomic_t no_neon = -1; /* not checked */
+
+   if (no_neon < 0)
+      no_neon = !png_have_neon(png_structp);
+
+   if (no_neon)
       return;
 #endif