8355077: Compiler error at splashscreen_gif.c due to unterminated string initialization

[YaSuenag]

I tried to build OpenJDK with GCC 15.0.1 on Fedora 42 x86_64, however I saw following error.

* For target support_native_java.desktop_libsplashscreen_splashscreen_gif.o:
/home/ysuenaga/github-forked/jdk/src/java.desktop/share/native/libsplashscreen/splashscreen_gif.c:51:41: error: initializer-string for array of ‘char’ truncates NUL terminator but destination lacks ‘nonstring’ attribute (12 chars into 11 available) [-Werror=unterminated-string-initialization]
   51 | static const char szNetscape20ext[11] = "NETSCAPE2.0";
      | ^~~~~~~~~~~~~
cc1: all warnings being treated as errors

This constant seems to be used to detect Netscape 2.0 extension in GIF image. It should be used to compare with extension block without NUL char, but we should tweak initialization to avoid this error for safety code.

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Issue

• JDK-8355077: Compiler error at splashscreen_gif.c due to unterminated string initialization (Bug - P4)

Reviewers

• Phil Race (@prrace - Reviewer)

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8355077: Compiler error at splashscreen_gif.c due to unterminated string initialization

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At the time when this comment was updated there had been 126 new commits pushed to the master branch:

• 5db62ab: 8315719: Adapt AOTClassLinking test case for dynamic CDS archive
• 2785570: 8355366: Fix the wrong usage of PassFailJFrame.forcePass() in some manual tests
• 4b88029: 8355439: Some hotspot/jtreg/serviceability/sa/* tests fail on static JDK due to explicit checks for shared libraries in process memory map
• ... and 123 more: https://git.openjdk.org/jdk/compare/128f2d1cadae3cf91e4c590e6dabe2086737b7dd...master

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[prrace]

Isn't gcc wrong to complain ?
I'm looking at what is admittedly an old draft of ANSI C
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
and on p130 it has this where t is the same as the usage in splashscreen.

======
EXAMPLE 8 The declaration

char s[] = "abc", t[3] = "abc";

defines ‘‘plain’’ char array objects s and t whose elements are initialized with character string literals.
This declaration is identical to

  char s[] = { 'a', 'b', 'c', '\0' },
          t[] = { 'a', 'b', 'c' };

=====

[YaSuenag]

I think this behavior is not a bug in GCC.

splashscreen_gif.c would be compiled with -Wextra, then -Wunterminated-string-initialization is enabled by default, then the warning would be reported as I shown.
https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wunterminated-string-initialization

As an option, we can set nonstring attribute as following. Similar use case in Linux Kernel has introduced in GCC bugzilla. Is this more suitable in this case?

diff --git a/src/java.desktop/share/native/libsplashscreen/splashscreen_gif.c b/src/java.desktop/share/native/libsplashscreen/splashscreen_gif.c
index 3654c677493..047f08835ad 100644
--- a/src/java.desktop/share/native/libsplashscreen/splashscreen_gif.c
+++ b/src/java.desktop/share/native/libsplashscreen/splashscreen_gif.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -48,7 +48,7 @@
                                 // restore the area overwritten by the graphic with
                                 // what was there prior to rendering the graphic.

-static const char szNetscape20ext[11] = "NETSCAPE2.0";
+static const char szNetscape20ext[11] __attribute__((nonstring)) = "NETSCAPE2.0";

 #define NSEXT_LOOP      0x01    // Loop Count field code

[prrace]

hmm. yes, it looks like it is enabled by -Wextra
https://gcc.gnu.org/pipermail/gcc-patches/2024-June/656014.html

Ok. let's make the change as the easiest thing to do.

[YaSuenag]

/integrate

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Going to push as commit 898d479.
Since your change was applied there have been 130 commits pushed to the master branch:

• 21b0f5e: 8355637: SSLSessionImpl's "serialization" list documentation is incorrectly ordered
• 3b3a055: 8342676: Unsigned Vector Min / Max transforms
• 91a9043: 8355562: RISC-V: Cleanup names of vector-scalar instructions in riscv_v.ad
• ... and 127 more: https://git.openjdk.org/jdk/compare/128f2d1cadae3cf91e4c590e6dabe2086737b7dd...master

Your commit was automatically rebased without conflicts.

[openjdk]

@YaSuenag Pushed as commit 898d479.

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