Re: [PATCH] target/ppc/kvm: Fix const violation when trimming CPU alias suffix

[Gautam Menghani <gautam@linux.ibm.com>]

On Mon, May 04, 2026 at 07:13:44PM +0530, Amit Machhiwal wrote:
> GCC 16 tightens diagnostics around const correctness and now correctly
> rejects attempts to modify strings referenced through const-qualified
> pointers. In kvm_ppc_register_host_cpu_type(), ppc_cpu_aliases[i].model
> is defined as const char *, but the code was using strstr() on it and
> then modifying the returned pointer in-place to strip
> POWERPC_CPU_TYPE_SUFFIX.
> 
> This results in a write through a pointer derived from const data,
> triggering a build failure with GCC 16:
> 
>   error: assignment discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
>         suffix = strstr(ppc_cpu_aliases[i].model, POWERPC_CPU_TYPE_SUFFIX);
>                ^
> 
> Fix this by duplicating the model string into a mutable buffer using
> g_strdup(), storing it in the alias table, and then performing the
> suffix truncation on the mutable copy.
> 
> This preserves the existing behavior while avoiding modification of
> const data and ensures compatibility with newer compilers.
> 
> No functional change intended.
> 
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> ---
>  target/ppc/kvm.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 25c28ad089c6..e71e5c0117da 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2654,10 +2654,12 @@ static int kvm_ppc_register_host_cpu_type(void)
>      dc = DEVICE_CLASS(ppc_cpu_get_family_class(pvr_pcc));
>      for (i = 0; ppc_cpu_aliases[i].alias != NULL; i++) {
>          if (g_ascii_strcasecmp(ppc_cpu_aliases[i].alias, dc->desc) == 0) {
> +            char *model;
>              char *suffix;
>  
> -            ppc_cpu_aliases[i].model = g_strdup(object_class_get_name(oc));
> -            suffix = strstr(ppc_cpu_aliases[i].model, POWERPC_CPU_TYPE_SUFFIX);
> +            model = g_strdup(object_class_get_name(oc));
> +            ppc_cpu_aliases[i].model = model;
> +            suffix = strstr(model, POWERPC_CPU_TYPE_SUFFIX);
>              if (suffix) {
>                  *suffix = 0;
>              }
> 

A const char * variable is ideally supposed to point to an immutable
string. But even with this fix, the string that
"ppc_cpu_aliases[i].model" points to is being changed after assignment.

Would the below diff (untested) be a better fix?

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 41bd03ec2a..a84e4b4636 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -2654,13 +2654,14 @@ static int kvm_ppc_register_host_cpu_type(void)
     dc = DEVICE_CLASS(ppc_cpu_get_family_class(pvr_pcc));
     for (i = 0; ppc_cpu_aliases[i].alias != NULL; i++) {
         if (strcasecmp(ppc_cpu_aliases[i].alias, dc->desc) == 0) {
-            char *suffix;
+            char *suffix, *model;
 
-            ppc_cpu_aliases[i].model = g_strdup(object_class_get_name(oc));
-            suffix = strstr(ppc_cpu_aliases[i].model, POWERPC_CPU_TYPE_SUFFIX);
+            model = g_strdup(object_class_get_name(oc));
+            suffix = strstr(model, POWERPC_CPU_TYPE_SUFFIX);
             if (suffix) {
                 *suffix = 0;
             }
+            ppc_cpu_aliases[i].model = model;
             break;
         }
     }