Re: [PATCH] libxl: constify some local variables to appease gcc 15.2.1

[Jan Beulich <jbeulich@xxxxxxxx>]

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@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> 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