Be more type-safe when calling setjmp(); call the same one that libpng would

Depending whether _BSD_SOURCE is preferred, glibc will provide one of two
implementations of setjmp()/longjmp() (it either does or doesn't save the
signal mask), acting on different definitions of the jmp_buf struct.

libpng calls longjmp() internally, and expects its callers to call the
version of setjmp() corresponding to the longjmp() call that libpng would
make.

In an attempt to ensure that consistent versions of setjmp() and longjmp()
are used, pngconf.h insists that on Linux, setjmp.h has not already been
included. However, quakedef.h includes that header, leading to some
interesting contortions when using the system libpng.

(IMO the right thing for libpng to do would be for it to provide an exported
function png_setjmp (or something) which calls the version of setjmp() that
libpng expects on the jmp_buf included in the png structure, like qpng_setjmp
in this patch.)

When using the system libpng headers, this patch also avoids the assumption
that jmp_buf is the first thing in the png structure.

diff --git a/image_png.c b/image_png.c
index 289b8d3eee20db48bbab3e368ded6a2a292548d2..dc3554d7fc3722dfa046ce64355f84c110978763 100644 (file)
--- a/image_png.c
+++ b/image_png.c
@@ -30,6 +30,12 @@
 // This has to come before anything else that includes setjmp.h, because
 // libpng specifically wants non-BSD setjmp semantics.
 # include <png.h>
+// Use the matching version of setjmp ourselves.
+static inline int
+my_setjmp (jmp_buf env)
+{
+       return setjmp (env);
+}
 #endif
 
 #include "quakedef.h"
@@ -38,6 +44,8 @@
 
 #ifdef LINK_TO_PNG
 
+#define qpng_setjmp(png) my_setjmp (png->jmpbuf)
+
 #define qpng_set_sig_bytes png_set_sig_bytes
 #define qpng_sig_cmp png_sig_cmp
 #define qpng_create_read_struct png_create_read_struct
@@ -108,17 +116,19 @@ static void                               (*qpng_write_info)                      (void*, void*);
 static void                            (*qpng_write_row)                       (void*, unsigned char*);
 static void                            (*qpng_write_end)                       (void*, void*);
 
-// libpng 1.4+ longjmp hack
-typedef void (*qpng_longjmp_ptr) (jmp_buf, int);
-static jmp_buf* (*qpng_set_longjmp_fn) (void *, qpng_longjmp_ptr, size_t);
-#define qpng_jmpbuf_14(png_ptr) (*qpng_set_longjmp_fn((png_ptr), longjmp, sizeof (jmp_buf)))
-
-// libpng 1.2 longjmp hack
-#define qpng_jmpbuf_12(png_ptr) (*((jmp_buf *) png_ptr))
-
-// all version support
-#define qpng_jmpbuf(png_ptr) \
-       (qpng_set_longjmp_fn ? qpng_jmpbuf_14(png_ptr) : qpng_jmpbuf_12(png_ptr))
+       // NOTE: this relies on jmp_buf being the first thing in the png structure
+       // created by libpng! (this is correct for libpng 1.2.x)
+#ifdef __cplusplus
+#ifdef WIN64
+#define qpng_setjmp(png) setjmp((_JBTYPE *)png)
+#elif defined(MACOSX) || defined(WIN32)
+#define qpng_setjmp(png) setjmp((int *)png)
+#else
+#define qpng_setjmp(png) setjmp((__jmp_buf_tag *)png)
+#endif
+#else
+#define qpng_setjmp(png) setjmp(png)
+#endif
 
 static dllfunction_t pngfuncs[] =
 {
@@ -366,7 +376,7 @@ unsigned char *PNG_LoadImage_BGRA (const unsigned char *raw, int filesize, int *
 
        // NOTE: this relies on jmp_buf being the first thing in the png structure
        // created by libpng! (this is correct for libpng 1.2.x)
-       if (setjmp(qpng_jmpbuf(png)))
+       if (qpng_setjmp(png))
        {
                if (my_png.Data)
                        Mem_Free(my_png.Data);
@@ -554,19 +564,7 @@ qboolean PNG_SaveImage_preflipped (const char *filename, int width, int height,
        // on the fields in this struct for cleanup
        memset(&my_png, 0, sizeof(my_png));
 
-       // NOTE: this relies on jmp_buf being the first thing in the png structure
-       // created by libpng! (this is correct for libpng 1.2.x)
-#ifdef __cplusplus
-#ifdef WIN64
-       if (setjmp((_JBTYPE *)png))
-#elif defined(MACOSX) || defined(WIN32)
-       if (setjmp((int *)png))
-#else
-       if (setjmp((__jmp_buf_tag *)png))
-#endif
-#else
-       if (setjmp(png))
-#endif
+       if (qpng_setjmp(png))
        {
                qpng_destroy_write_struct(&png, &pnginfo);
                return false;