Archlinux just updated gcc to 15.2.1+r604+g0b99615a8aef-1 and that
complains about libxl:

    libxl_cpuid.c: In function ‘libxl_cpuid_parse_config_xend’:
    libxl_cpuid.c:447:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
      447 |         endptr = strchr(str, '=');
          |                ^
    libxl_cpuid.c:452:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
      452 |         endptr = strchr(str, ',');
          |                ^
    libxl_cpuid.c:454:20: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
      454 |             endptr = strchr(str, 0);
          |                    ^
    libxl_cpuid.c: In function ‘libxl_cpuid_parse_config_xend’:
    libxl_cpuid.c:447:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
      447 |         endptr = strchr(str, '=');
          |                ^
    libxl_cpuid.c:452:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
      452 |         endptr = strchr(str, ',');
          |                ^
    libxl_cpuid.c:454:20: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
      454 |             endptr = strchr(str, 0);
          |                    ^
    cc1: all warnings being treated as errors

Add missing consts. Note in libxl_cpuid_parse_config_xend() non-const
endptr still is needed, to be compatible with the second argument to
strtoul(). Add second variable for this reason.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
When I say "just updated" I really mean it. The update hit me between my
CI saying "ok" and release build few hours later. I guess Xen's CI will
see that only after next refresh of the Arch container (next week?).
---
 tools/libs/light/libxl_cpuid.c    | 19 ++++++++++---------
 tools/libs/light/libxl_internal.c |  2 +-
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/tools/libs/light/libxl_cpuid.c b/tools/libs/light/libxl_cpuid.c
index 8420b2465f39..5fb580113d80 100644
--- a/tools/libs/light/libxl_cpuid.c
+++ b/tools/libs/light/libxl_cpuid.c
@@ -415,6 +415,7 @@ int libxl_cpuid_parse_config_xend(libxl_cpuid_policy_list *policy,
                                   const char* str)
 {
     char *endptr;
+    const char *endptrc;
     unsigned long value;
     uint32_t leaf, subleaf = XEN_CPUID_INPUT_UNUSED;
     struct xc_xend_cpuid *entry;
@@ -444,25 +445,25 @@ int libxl_cpuid_parse_config_xend(libxl_cpuid_policy_list *policy,
             return 4;
         }
         value = str[1] - 'a';
-        endptr = strchr(str, '=');
-        if (value > 3 || endptr == NULL) {
+        endptrc = strchr(str, '=');
+        if (value > 3 || endptrc == NULL) {
             return 4;
         }
-        str = endptr + 1;
-        endptr = strchr(str, ',');
-        if (endptr == NULL) {
-            endptr = strchr(str, 0);
+        str = endptrc + 1;
+        endptrc = strchr(str, ',');
+        if (endptrc == NULL) {
+            endptrc = strchr(str, 0);
         }
-        if (endptr - str != 32) {
+        if (endptrc - str != 32) {
             return 5;
         }
         entry->policy[value] = calloc(32 + 1, 1);
         strncpy(entry->policy[value], str, 32);
         entry->policy[value][32] = 0;
-        if (*endptr == 0) {
+        if (*endptrc == 0) {
             break;
         }
-        for (str = endptr + 1; *str == ' ' || *str == '\n'; str++);
+        for (str = endptrc + 1; *str == ' ' || *str == '\n'; str++);
     }
     return 0;
 }
diff --git a/tools/libs/light/libxl_internal.c b/tools/libs/light/libxl_internal.c
index 2941ca0bbd0e..d70cfed7d88f 100644
--- a/tools/libs/light/libxl_internal.c
+++ b/tools/libs/light/libxl_internal.c
@@ -204,7 +204,7 @@ char *libxl__strndup(libxl__gc *gc, const char *c, size_t n)
 
 char *libxl__dirname(libxl__gc *gc, const char *s)
 {
-    char *c = strrchr(s, '/');
+    const char *c = strrchr(s, '/');
 
     if (!c)
         return NULL;
-- 
2.51.0

On 12.02.2026 04:23, Marek Marczykowski-Górecki wrote:
> Archlinux just updated gcc to 15.2.1+r604+g0b99615a8aef-1 and that
> complains about libxl:
> 
>     libxl_cpuid.c: In function ‘libxl_cpuid_parse_config_xend’:
>     libxl_cpuid.c:447:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
>       447 |         endptr = strchr(str, '=');
>           |                ^
>     libxl_cpuid.c:452:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
>       452 |         endptr = strchr(str, ',');
>           |                ^
>     libxl_cpuid.c:454:20: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
>       454 |             endptr = strchr(str, 0);
>           |                    ^
>     libxl_cpuid.c: In function ‘libxl_cpuid_parse_config_xend’:
>     libxl_cpuid.c:447:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
>       447 |         endptr = strchr(str, '=');
>           |                ^
>     libxl_cpuid.c:452:16: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
>       452 |         endptr = strchr(str, ',');
>           |                ^
>     libxl_cpuid.c:454:20: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
>       454 |             endptr = strchr(str, 0);
>           |                    ^
>     cc1: all warnings being treated as errors

That's supposed to be happening in C23 mode only, isn't it? Looks like under
tools/ we don't set the mode we want to compile in.

> Add missing consts. Note in libxl_cpuid_parse_config_xend() non-const
> endptr still is needed, to be compatible with the second argument to
> strtoul(). Add second variable for this reason.
> 
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> ---
> When I say "just updated" I really mean it. The update hit me between my
> CI saying "ok" and release build few hours later. I guess Xen's CI will
> see that only after next refresh of the Arch container (next week?).

Hmm, and that would then affect not only stable trees, but also security-
only ones. In particular there I'd wonder whether enforcing mode (to be e.g.
C99) wouldn't be more appropriate. Anthony?

> --- a/tools/libs/light/libxl_cpuid.c
> +++ b/tools/libs/light/libxl_cpuid.c
> @@ -415,6 +415,7 @@ int libxl_cpuid_parse_config_xend(libxl_cpuid_policy_list *policy,
>                                    const char* str)
>  {
>      char *endptr;
> +    const char *endptrc;

Don't know what the (perhaps unwritten) policy in libxl is, but in the
hypervisor I'd ask for the variable to be declared in the more narrow scope
it's solely used in.

> @@ -444,25 +445,25 @@ int libxl_cpuid_parse_config_xend(libxl_cpuid_policy_list *policy,
>              return 4;
>          }
>          value = str[1] - 'a';
> -        endptr = strchr(str, '=');
> -        if (value > 3 || endptr == NULL) {
> +        endptrc = strchr(str, '=');
> +        if (value > 3 || endptrc == NULL) {
>              return 4;
>          }
> -        str = endptr + 1;
> -        endptr = strchr(str, ',');
> -        if (endptr == NULL) {
> -            endptr = strchr(str, 0);
> +        str = endptrc + 1;
> +        endptrc = strchr(str, ',');
> +        if (endptrc == NULL) {
> +            endptrc = strchr(str, 0);
>          }
> -        if (endptr - str != 32) {
> +        if (endptrc - str != 32) {
>              return 5;
>          }
>          entry->policy[value] = calloc(32 + 1, 1);
>          strncpy(entry->policy[value], str, 32);
>          entry->policy[value][32] = 0;
> -        if (*endptr == 0) {
> +        if (*endptrc == 0) {
>              break;
>          }
> -        for (str = endptr + 1; *str == ' ' || *str == '\n'; str++);
> +        for (str = endptrc + 1; *str == ' ' || *str == '\n'; str++);

I'd further ask for the semicolon to be moved to its own line.

Jan