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, 4 insertions, 18 deletions

diff --git a/include/mupdf/fitz/context.h b/include/mupdf/fitz/context.h
index 905a82ef..cb083f87 100644
--- a/include/mupdf/fitz/context.h
+++ b/include/mupdf/fitz/context.h
@@ -49,18 +49,9 @@ void fz_var_imp(void *);
 	attention to the man behind the curtain.
 */
 
-/*
-	OK, so you looked behind the curtain, and you're wondering why we use
-	an inline function for fz_trying, rather than doing a bare assignment
-	and test. See bug 696115. Various versions of gcc (depressingly,
-	modern ones) cause problems under optimisation whereby the value
-	returned from setjmp is not written correctly. This causes the rest
-	of the try/catch to behave incorrectly. The use of a function call
-	here suffices to solve it.
-*/
 #define fz_try(ctx) \
-	if (fz_push_try(ctx->error) && \
-		fz_trying(ctx->error, fz_setjmp(ctx->error->stack[ctx->error->top].buffer)))\
+	{{{ fz_push_try(ctx->error); \
+	if (fz_setjmp(ctx->error->stack[ctx->error->top].buffer) == 0)\
 	{ do {
 
 #define fz_always(ctx) \
@@ -73,15 +64,10 @@ void fz_var_imp(void *);
 
 #define fz_catch(ctx) \
 		} while(0); \
-	} \
+	} }}} \
 	if (ctx->error->stack[ctx->error->top--].code > 1)
 
-int fz_push_try(fz_error_context *ex);
-static inline int fz_trying(fz_error_context *error, int value)
-{
-	error->stack[error->top].code = value;
-	return value == 0;
-}
+void fz_push_try(fz_error_context *ex);
 FZ_NORETURN void fz_throw(fz_context *, int errcode, const char *, ...) __printflike(3, 4);
 FZ_NORETURN void fz_rethrow(fz_context *);
 FZ_NORETURN void fz_rethrow_message(fz_context *, const char *, ...)  __printflike(2, 3);