From 2a23247420094c8f576dd6ec30978fe418355336 Mon Sep 17 00:00:00 2001
From: John Bowler <jbowler@acm.org>
Date: Sun, 14 Jan 2024 15:47:20 -0800
Subject: [PATCH] pngcp: remove GNU setjmp warning workround

Prior versons of the GCC warned about the 'dest' parameter of
contrib/tools/pngcp.c not being volatile, which isn't necessary because
it isn't modified.  This removes the GCC specific fixup.

The function which calls setjmp, cppng() also relied on undefined
behavior because it assigned the result of setjmp() to a variable; this
is not one of the four uses of setjmp permitted by ANSI-C.  This passes
the result previously returned by longjmp via (struct display).  It's
very very unlikely that any compiler could have got the code wrong but
it is technically undefined.
---
 contrib/tools/pngcp.c | 32 +++++++++++---------------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/contrib/tools/pngcp.c b/contrib/tools/pngcp.c
index 579e28d2b..cf621fa5b 100644
--- a/contrib/tools/pngcp.c
+++ b/contrib/tools/pngcp.c
@@ -1,6 +1,6 @@
 /* pngcp.c
  *
- * Copyright (c) 2016,2022 John Cunningham Bowler
+ * Copyright (c) 2016,2022,2024 John Cunningham Bowler
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -88,16 +88,6 @@
 #  define voidcast(type, value) (value)
 #endif /* __cplusplus */
 
-#ifdef __GNUC__
-   /* Many versions of GCC erroneously report that local variables unmodified
-    * within the scope of a setjmp may be clobbered.  This hacks round the
-    * problem (sometimes) without harming other compilers.
-    */
-#  define gv volatile
-#else
-#  define gv
-#endif
-
 /* 'CLOCK_PROCESS_CPUTIME_ID' is one of the clock timers for clock_gettime.  It
  * need not be supported even when clock_gettime is available.  It returns the
  * 'CPU' time the process has consumed.  'CPU' time is assumed to include time
@@ -395,6 +385,7 @@ struct display
 {
    jmp_buf          error_return;      /* Where to go to on error */
    unsigned int     errset;            /* error_return is set */
+   int              errlevel;          /* error level from longjmp */
 
    const char      *operation;         /* What is happening */
    const char      *filename;          /* The name of the original file */
@@ -634,7 +625,10 @@ display_log(struct display *dp, error_level level, const char *fmt, ...)
    if (level > APP_FAIL || (level > ERRORS && !(dp->options & CONTINUE)))
    {
       if (dp->errset)
+      {
+         dp->errlevel = level;
          longjmp(dp->error_return, level);
+      }
 
       else
          exit(99);
@@ -2318,14 +2312,9 @@ cp_one_file(struct display *dp, const char *filename, const char *destname)
 }
 
 static int
-cppng(struct display *dp, const char *file, const char *gv dest)
-   /* Exists solely to isolate the setjmp clobbers which some versions of GCC
-    * erroneously generate.
-    */
+cppng(struct display *dp, const char *file, const char *dest)
 {
-   int ret = setjmp(dp->error_return);
-
-   if (ret == 0)
+   if (setjmp(dp->error_return) == 0)
    {
       dp->errset = 1;
       cp_one_file(dp, file, dest);
@@ -2337,10 +2326,11 @@ cppng(struct display *dp, const char *file, const char *gv dest)
    {
       dp->errset = 0;
 
-      if (ret < ERRORS) /* shouldn't longjmp on warnings */
-         display_log(dp, INTERNAL_ERROR, "unexpected return code %d", ret);
+      if (dp->errlevel < ERRORS) /* shouldn't longjmp on warnings */
+         display_log(dp, INTERNAL_ERROR, "unexpected return code %d",
+               dp->errlevel);
 
-      return ret;
+      return dp->errlevel;
    }
 }