ami_parse_bdf() discards const from strchr() result. Build fails under C23 + glibc ≥ 2.41 (Ubuntu 26.04)

[amd-vserbu]

Component: sw/AMI/api/src/ami.c

Summary

ami_parse_bdf() assigns the result of strchr() (called on a const char *) into a non-const char *. This silently discarded const on older toolchains, but is now a hard error when building in C23 mode against glibc ≥ 2.41, which ships C23 const-correct strchr overloads. Because api/Makefile builds with -Wall -Werror, the warning is fatal.

Affected code

sw/AMI/api/src/ami.c, ami_parse_bdf():

uint16_t ami_parse_bdf(const char *bdf)
{
    ...
    char *c = NULL;            /* line 386 */
    ...
    c = strchr(bdf, ':');      /* line 392 — const discarded here */
    if (c && ((size_t)(c - bdf) == BDF_DOMAIN_END))
        ...
}

bdf is const char *. With the C23 declaration of strchr, the return type is const char *, so assigning to char *c discards the qualifier. c is only ever used for strchr's result, a null check, and the pointer subtraction (c - bdf) — it is never used to mutate the string.

Diagnostic

ami.c:392:11: error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  392 |         c = strchr(bdf, ':');
      |           ^
cc1: all warnings being treated as errors

Build flags from sw/AMI/api/Makefile: -Wall -Werror, no explicit -std= (so the compiler default applies).

Root cause

The trigger is the combination of C23 mode and glibc ≥ 2.41, not a specific GCC version:

• glibc 2.41 added C23 const-correct overloads to <string.h>: it now declares both char *strchr(char *) and const char *strchr(const char *). For a const char * argument, strchr returns const char *.
• In C17 and earlier, <string.h> declares only the legacy char *strchr(const char *), so the assignment is valid.
• GCC 15 defaults to C23, so it fails out of the box; earlier GCC only fails when -std=gnu23/-std=c23 is passed explicitly.

Reproduction matrix

Original code, -Wall -Werror:

Distro	GCC	glibc	default std	-std=gnu17	-std=gnu23
Ubuntu 24.04	11.5 / 12.4 / 13.3 / 14.2	2.39	pass	pass	pass
Ubuntu 26.04	14.3	2.43	pass	pass	fail
Ubuntu 26.04	15.2	2.43	fail	pass	fail

Minimal reproducer

#include <string.h>
#include <stddef.h>

size_t first_colon_offset(const char *s)
{
    char *c = strchr(s, ':');           /* discards const under C23 + glibc>=2.41 */
    return c ? (size_t)(c - s) : 0;
}

gcc -std=gnu23 -Wall -Werror -c repro.c   # fails on glibc >= 2.41
gcc -std=gnu17 -Wall -Werror -c repro.c   # passes

Suggested fix

Declare the cursor as const char *, which is correct in all language modes since the pointer is never used to mutate the string:

-    char *c = NULL;
+    const char *c = NULL;

This compiles cleanly across all GCC versions, glibc versions, and standard modes tested.