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Re: [PATCH 17/17] target/s390x/cpu_models: Fix missing ERRP_GUARD() for


From: Thomas Huth
Subject: Re: [PATCH 17/17] target/s390x/cpu_models: Fix missing ERRP_GUARD() for error_prepend()
Date: Thu, 29 Feb 2024 18:17:24 +0100
User-agent: Mozilla Thunderbird

On 29/02/2024 15.39, Zhao Liu wrote:
From: Zhao Liu <zhao1.liu@intel.com>

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.

ERRP_GUARD() could avoid the case when @errp is the pointer of
error_fatal, the user can't see this additional information, because
exit() happens in error_setg earlier than information is added [1].

In target/s390x/cpu_models.c, there're 2 functions passing @errp to
error_prepend() without ERRP_GUARD():
- check_compatibility()
- s390_realize_cpu_model()

Though both their @errp parameters point to their callers' local @err
virables and don't cause the issue as [1] said, to follow the
requirement of @errp, also add missing ERRP_GUARD() at their beginning.

[1]: Issue description in the commit message of commit ae7c80a7bd73
      ("error: New macro ERRP_GUARD()").

Cc: David Hildenbrand <david@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
  target/s390x/cpu_models.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
index a63d990e4e8e..1a1c09612271 100644
--- a/target/s390x/cpu_models.c
+++ b/target/s390x/cpu_models.c
@@ -503,6 +503,7 @@ static void error_prepend_missing_feat(const char *name, 
void *opaque)
  static void check_compatibility(const S390CPUModel *max_model,
                                  const S390CPUModel *model, Error **errp)
  {
+    ERRP_GUARD();
      S390FeatBitmap missing;
if (model->def->gen > max_model->def->gen) {
@@ -566,6 +567,7 @@ S390CPUModel *get_max_cpu_model(Error **errp)
void s390_realize_cpu_model(CPUState *cs, Error **errp)
  {
+    ERRP_GUARD();
      Error *err = NULL;

I think that function could use an additional clean-up now: Remove the local "err" variable and use "errp" only instead.

 Thomas


      S390CPUClass *xcc = S390_CPU_GET_CLASS(cs);
      S390CPU *cpu = S390_CPU(cs);




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