Bug 696115: Further fix for setjmp/longjmp.

Tor turned up an interesting section in the C spec about this. See
page 275 of http://open-std.org/jtc1/sc22/wg14/www/docs/n1494.pdf
regarding acceptable places for setjmp to occur.

It seems that:

  if (setjmp(buf))
  if (!setjmp(buf))
  if (setjmp(buf) {==,!=,<,>} <integer constant>)

etc are all valid things to do, but assignments (and subsequent
testing of values) like:

  if ((code = setjmp(buf)) == 0)

are not allowed.

Further, it's not even clear that:

 if (a() && setjmp(buf))

is permissible.

We therefore recast the macros into the form:

  a();
  if (setjmp((buf)) == 0)

which should be acceptable under the C spec.

To keep try atomic, we introduce a block '{{{' around this, along
with a matching close block '}}}' in the catch clause. This has the
nifty extra effect of giving us a compile time error if we mismatch
our try/catches.

1 files changed, 12 insertions, 9 deletions

diff --git a/source/fitz/error.c b/source/fitz/error.c
index 414b993f..6d0b831d 100644
--- a/source/fitz/error.c
+++ b/source/fitz/error.c
@@ -86,7 +86,8 @@ static void throw(fz_error_context *ex)
 {
 	if (ex->top >= 0)
 	{
-		fz_longjmp(ex->stack[ex->top].buffer, ex->stack[ex->top].code + 2);
+		ex->stack[ex->top].code += 2;
+		fz_longjmp(ex->stack[ex->top].buffer, ex->stack[ex->top].code);
 	}
 	else
 	{
@@ -101,23 +102,25 @@ static void throw(fz_error_context *ex)
 	}
 }
 
-int fz_push_try(fz_error_context *ex)
+void fz_push_try(fz_error_context *ex)
 {
-	assert(ex);
 	ex->top++;
 	/* Normal case, get out of here quick */
 	if (ex->top < nelem(ex->stack)-1)
-		return 1; /* We exit here, and the setjmp sets the code to 0 */
+	{
+		ex->stack[ex->top].code = 0;
+		return;
+	}
 	/* We reserve the top slot on the exception stack purely to cope with
 	 * the case when we overflow. If we DO hit this, then we 'throw'
-	 * immediately - returning 0 stops the setjmp happening and takes us
-	 * direct to the always/catch clauses. */
-	assert(ex->top == nelem(ex->stack)-1);
+	 * immediately. */
+	assert(ex->top == nelem(ex->stack));
+	ex->top--;
+	ex->errcode = FZ_ERROR_GENERIC;
 	strcpy(ex->message, "exception stack overflow!");
-	ex->stack[ex->top].code = 2;
 	fprintf(stderr, "error: %s\n", ex->message);
 	LOGE("error: %s\n", ex->message);
-	return 0;
+	throw(ex);
 }
 
 int fz_caught(fz_context *ctx)