De-volatilize the internal implementation of `png_safe_execute`

`png_safe_execute` called `setjmp` in a context where the result was
undefined (an assignment statement). This corrects the code and removes
volatile statements that were introduced previously to quell warnings
from earlier versions of GCC.

Co-authored-by: John Bowler <jbowler@acm.org>

1 files changed, 10 insertions, 16 deletions

diff --git a/pngerror.c b/pngerror.c
index 53e79bacb..3469959a6 100644
--- a/pngerror.c
+++ b/pngerror.c
@@ -933,31 +933,25 @@ png_safe_warning(png_structp png_nonconst_ptr, png_const_charp warning_message)
 #endif
 
 int /* PRIVATE */
-png_safe_execute(png_imagep image_in, int (*function)(png_voidp), png_voidp arg)
+png_safe_execute(png_imagep image, int (*function)(png_voidp), png_voidp arg)
 {
-   volatile png_imagep image = image_in;
-   volatile int result;
-   volatile png_voidp saved_error_buf;
+   png_voidp saved_error_buf = image->opaque->error_buf;
    jmp_buf safe_jmpbuf;
+   int result;
 
-   /* Safely execute function(arg) with png_error returning to this function. */
-   saved_error_buf = image->opaque->error_buf;
-   result = setjmp(safe_jmpbuf) == 0;
-
-   if (result != 0)
+   /* Safely execute function(arg), with png_error returning back here. */
+   if (setjmp(safe_jmpbuf) == 0)
    {
-
       image->opaque->error_buf = safe_jmpbuf;
       result = function(arg);
+      image->opaque->error_buf = saved_error_buf;
+      return result;
    }
 
+   /* On png_error, return via longjmp, pop the jmpbuf, and free the image. */
    image->opaque->error_buf = saved_error_buf;
-
-   /* And do the cleanup prior to any failure return. */
-   if (result == 0)
-      png_image_free(image);
-
-   return result;
+   png_image_free(image);
+   return 0;
 }
 #endif /* SIMPLIFIED READ || SIMPLIFIED_WRITE */
 #endif /* READ || WRITE */