Re: [PATCH v2] target/ppc/kvm: Fix const violation when trimming CPU alias suffix

2026-05-12 Thread Harsh Prateek Bora 

Hi Vaibhav,

Thanks for taking a look ...

On 11/05/26 6:40 pm, Vaibhav Jain 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 copying only the needed suffix from the object class-name to
'ppc_cpu_aliases.model' using g_strdup and g_strndup, which maintains the
constness of the allocated buffer assigned to 'ppc_cpu_aliases.model'
member of the 'ppc_cpu_aliases' struct array.

The patch also adds error handling for possible memory allocation failure
while calling g_str{n}dup functions so that the error is properly
propogated back from kvm_arch_init().

Signed-off-by: Amit Machhiwal 
Signed-off-by: Vaibhav Jain (IBM) 

---
Change-log:

v1->v2:
https://lore.kernel.org/all/[email protected]
* Avoid pointer aliasing
* Handle memory allocation failure error
---
  target/ppc/kvm.c | 18 ++
  1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 25c28ad089..42cd4f4fff 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -170,9 +170,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
  
  cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);

  cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
-kvm_ppc_register_host_cpu_type();
  
-return 0;

+return kvm_ppc_register_host_cpu_type();
  }
  
  int kvm_arch_irqchip_create(KVMState *s)

@@ -2654,14 +2653,17 @@ 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 *suffix;
+const gchar *suffix, *cname = object_class_get_name(oc);
+
+suffix = g_strstr_len(cname, -1, POWERPC_CPU_TYPE_SUFFIX);
+ppc_cpu_aliases[i].model = unlikely(suffix) ?
+g_strndup(cname, suffix - cname) : g_strdup(cname);
  
-ppc_cpu_aliases[i].model = g_strdup(object_class_get_name(oc));

-suffix = strstr(ppc_cpu_aliases[i].model, POWERPC_CPU_TYPE_SUFFIX);
-if (suffix) {
-*suffix = 0;
+if (!ppc_cpu_aliases[i].model) {
+return -ENOMEM;


IIUC, g_strndup will abort the program in case of OOM eventually making
it a dead code. We may consider using g_try_strndup at all if needed.
Also, not sure if we really need unlikely() and a typecast may be needed 
for (suffix - cname).


However, can we keep OOM related changes in a separate patch and keep 
only GCC16 build breakage fix in this patch retaining the original patch 
authorship with delta changes attributed alongside respective SoB?


Thanks
Harsh


+} else {
+return 0;
  }
-break;
  }
  }

[PATCH v2] target/ppc/kvm: Fix const violation when trimming CPU alias suffix

2026-05-11 Thread Vaibhav Jain 
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 copying only the needed suffix from the object class-name to
'ppc_cpu_aliases.model' using g_strdup and g_strndup, which maintains the
constness of the allocated buffer assigned to 'ppc_cpu_aliases.model'
member of the 'ppc_cpu_aliases' struct array.

The patch also adds error handling for possible memory allocation failure
while calling g_str{n}dup functions so that the error is properly
propogated back from kvm_arch_init().

Signed-off-by: Amit Machhiwal 
Signed-off-by: Vaibhav Jain (IBM) 

---
Change-log:

v1->v2:
https://lore.kernel.org/all/[email protected]
* Avoid pointer aliasing
* Handle memory allocation failure error
---
 target/ppc/kvm.c | 18 ++
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 25c28ad089..42cd4f4fff 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -170,9 +170,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
 
 cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
 cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
-kvm_ppc_register_host_cpu_type();
 
-return 0;
+return kvm_ppc_register_host_cpu_type();
 }
 
 int kvm_arch_irqchip_create(KVMState *s)
@@ -2654,14 +2653,17 @@ 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 *suffix;
+const gchar *suffix, *cname = object_class_get_name(oc);
+
+suffix = g_strstr_len(cname, -1, POWERPC_CPU_TYPE_SUFFIX);
+ppc_cpu_aliases[i].model = unlikely(suffix) ?
+g_strndup(cname, suffix - cname) : g_strdup(cname);
 
-ppc_cpu_aliases[i].model = g_strdup(object_class_get_name(oc));
-suffix = strstr(ppc_cpu_aliases[i].model, POWERPC_CPU_TYPE_SUFFIX);
-if (suffix) {
-*suffix = 0;
+if (!ppc_cpu_aliases[i].model) {
+return -ENOMEM;
+} else {
+return 0;
 }
-break;
 }
 }
 
-- 
2.54.0

Re: [PATCH v2] target/ppc/kvm: Fix const violation when trimming CPU alias suffix

2026-05-08 Thread Gautam Menghani 
On Fri, May 08, 2026 at 01:44:16PM +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 declared 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(), trimming the suffix on that temporary buffer, and only then
> storing it in the alias table.
> 
> 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 
> ---
> Changes in v2:
>   * trim the duplicated buffer before assigning it to ppc_cpu_aliases[i].model
> ---
> 
>  target/ppc/kvm.c | 7 ---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 25c28ad089c6..c2843b1421cb 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 (g_ascii_strcasecmp(ppc_cpu_aliases[i].alias, dc->desc) == 0) {
> -char *suffix;
> +char *model, *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));
> +suffix = strstr(model, POWERPC_CPU_TYPE_SUFFIX);
>  if (suffix) {
>  *suffix = 0;
>  }
> +ppc_cpu_aliases[i].model = model;
>  break;
>  }
>  }
> 


Reviewed-by: Gautam Menghani 

> base-commit: ee7eb612be8f8886d48c1d0c1f1c65e495138f83
> -- 
> 2.50.1 (Apple Git-155)
> 
>

[PATCH v2] target/ppc/kvm: Fix const violation when trimming CPU alias suffix

2026-05-08 Thread Amit Machhiwal 
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 declared 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(), trimming the suffix on that temporary buffer, and only then
storing it in the alias table.

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 
---
Changes in v2:
  * trim the duplicated buffer before assigning it to ppc_cpu_aliases[i].model
---

 target/ppc/kvm.c | 7 ---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 25c28ad089c6..c2843b1421cb 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 (g_ascii_strcasecmp(ppc_cpu_aliases[i].alias, dc->desc) == 0) {
-char *suffix;
+char *model, *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));
+suffix = strstr(model, POWERPC_CPU_TYPE_SUFFIX);
 if (suffix) {
 *suffix = 0;
 }
+ppc_cpu_aliases[i].model = model;
 break;
 }
 }

base-commit: ee7eb612be8f8886d48c1d0c1f1c65e495138f83
-- 
2.50.1 (Apple Git-155)