fs/proc: fix build with GCC 15 due to -Werror=unterminated-string-initialization

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>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 72f14fd59c2d01aaeac216cdd24c8006e2f875b5..e52bd96137a62e78badbbf7a42e522f4a871e1fe 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -909,8 +909,15 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 {
        /*
         * 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 seq_file *m, struct vm_area_struct *vma)
        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');
 }