+ fs-proc-fix-build-with-gcc-15-due-to-werror=unterminated-string-initialization.patch added to mm-hotfixes-unstable branch

+ fs-proc-fix-build-with-gcc-15-due-to-werror=unterminated-string-initialization.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: fs/proc: fix build with GCC 15 due to -Werror=unterminated-string-initialization
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     fs-proc-fix-build-with-gcc-15-due-to-werror=unterminated-string-initialization.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-proc-fix-build-with-gcc-15-due-to-werror=unterminated-string-initialization.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Brahmajit Das <brahmajit.xyz@gmail.com>
Subject: fs/proc: fix build with GCC 15 due to -Werror=unterminated-string-initialization
Date: Sat, 5 Oct 2024 12:07:00 +0530

show show_smap_vma_flags() has been a using misspelled initializer in
mnemonics[] - it needed to initialize 2 element array of char and it used
NUL-padded 2 character string literals (i.e.  3-element initializer).

This has been spotted by gcc-15[*]; prior to that gcc quietly dropped the
3rd eleemnt of initializers.  To fix this we are increasing the size of
mnemonics[] (from mnemonics[BITS_PER_LONG][2] to
mnemonics[BITS_PER_LONG][3]) to accomodate the NUL-padded string literals.

This also helps us in simplyfying the logic for printing of the flags as
instead of printing each character from the mnemonics[], we can just print
the mnemonics[] using seq_printf.

[*]: fs/proc/task_mmu.c:917:49: error: initializer-string for array of `char' is too long [-Werror=unterminate d-string-initialization]
  917 |                 [0 ... (BITS_PER_LONG-1)] = "??",
      |                                                 ^~~~
fs/proc/task_mmu.c:917:49: error: initializer-string for array of `char' is too long [-Werror=unterminate d-string-initialization]
fs/proc/task_mmu.c:917:49: error: initializer-string for array of `char' is too long [-Werror=unterminate d-string-initialization]
fs/proc/task_mmu.c:917:49: error: initializer-string for array of `char' is too long [-Werror=unterminate d-string-initialization]
fs/proc/task_mmu.c:917:49: error: initializer-string for array of `char' is too long [-Werror=unterminate d-string-initialization]
fs/proc/task_mmu.c:917:49: error: initializer-string for array of `char' is too long [-Werror=unterminate d-string-initialization]
...


Stephen pointed out:

: The C standard explicitly allows for a string initializer to be too long
: due to the NUL byte at the end ...  so this warning may be overzealous.

but let's make the warning go away anwyay.

Link: https://lkml.kernel.org/r/20241005063700.2241027-1-brahmajit.xyz@gmail.com
Link: https://lkml.kernel.org/r/20241003093040.47c08382@canb.auug.org.au
Signed-off-by: Brahmajit Das <brahmajit.xyz@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/task_mmu.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

--- a/fs/proc/task_mmu.c~fs-proc-fix-build-with-gcc-15-due-to-werror=unterminated-string-initialization
+++ a/fs/proc/task_mmu.c
@@ -909,8 +909,15 @@ static void show_smap_vma_flags(struct s
 {
 	/*
 	 * Don't forget to update Documentation/ on changes.
+	 *
+	 * The length of the second argument of mnemonics[]
+	 * needs to be 3 instead of previously set 2
+	 * (i.e. from [BITS_PER_LONG][2] to [BITS_PER_LONG][3])
+	 * to avoid spurious
+	 * -Werror=unterminated-string-initialization warning
+	 *  with GCC 15
 	 */
-	static const char mnemonics[BITS_PER_LONG][2] = {
+	static const char mnemonics[BITS_PER_LONG][3] = {
 		/*
 		 * In case if we meet a flag we don't know about.
 		 */
@@ -987,11 +994,8 @@ static void show_smap_vma_flags(struct s
 	for (i = 0; i < BITS_PER_LONG; i++) {
 		if (!mnemonics[i][0])
 			continue;
-		if (vma->vm_flags & (1UL << i)) {
-			seq_putc(m, mnemonics[i][0]);
-			seq_putc(m, mnemonics[i][1]);
-			seq_putc(m, ' ');
-		}
+		if (vma->vm_flags & (1UL << i))
+			seq_printf(m, "%s ", mnemonics[i]);
 	}
 	seq_putc(m, '\n');
 }
_

Patches currently in -mm which might be from brahmajit.xyz@gmail.com are

fs-proc-fix-build-with-gcc-15-due-to-werror=unterminated-string-initialization.patch