[PATCH] gdb: fix assert after register write failure

[PATCH] gdb: fix assert after register write failure

[Stephan Rohr]

From: Eduard Sargsyan <eduard.sargsyan@intel.com>

GDB tries to invalidate register cache if write to register fails.  In case
when write was requested to be done for a remote inferior and connection with
remote is dead (so write request will fail) GDB cleans register caches and as
result setting register status fails with segmentation fault, because internal
pointers are not valid anymore and the unique_ptr with register status is
null.

This change adds check if register status cache is still valid before trying to
modify (set status to UNKNOWN).
---
 gdb/regcache.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/gdb/regcache.c b/gdb/regcache.c
index 773e8ac37d0..01c60ea8047 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -883,8 +883,11 @@ regcache::raw_write (int regnum, gdb::array_view<const gdb_byte> src)
 
   /* Invalidate the register after it is written, in case of a
      failure.  */
-  auto invalidator
-    = make_scope_exit ([&] { this->invalidate (regnum); });
+  auto invalidator = make_scope_exit ([&]
+    {
+      if (this->m_register_status != nullptr)
+	this->invalidate (regnum);
+    });
 
   target_store_registers (this, regnum);
 
-- 
2.43.0

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Re: [PATCH] gdb: fix assert after register write failure

[Guinevere Larsen]

On 10/12/26 7:38 AM, Stephan Rohr wrote:
> From: Eduard Sargsyan <eduard.sargsyan@intel.com>
>
> GDB tries to invalidate register cache if write to register fails.  In case
> when write was requested to be done for a remote inferior and connection with
> remote is dead (so write request will fail) GDB cleans register caches and as
> result setting register status fails with segmentation fault, because internal
> pointers are not valid anymore and the unique_ptr with register status is
> null.
>
> This change adds check if register status cache is still valid before trying to
> modify (set status to UNKNOWN).
> ---

Hi! Thanks for working on this!

I wonder if it would be better to move this check to 
regcache::invalidate instead, so that we don't need to make this check 
every time invalidate is called in this kind of situation.

-- 
Cheers,
Guinevere Larsen
it/its
she/her (deprecated)

>   gdb/regcache.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/regcache.c b/gdb/regcache.c
> index 773e8ac37d0..01c60ea8047 100644
> --- a/gdb/regcache.c
> +++ b/gdb/regcache.c
> @@ -883,8 +883,11 @@ regcache::raw_write (int regnum, gdb::array_view<const gdb_byte> src)
>   
>     /* Invalidate the register after it is written, in case of a
>        failure.  */
> -  auto invalidator
> -    = make_scope_exit ([&] { this->invalidate (regnum); });
> +  auto invalidator = make_scope_exit ([&]
> +    {
> +      if (this->m_register_status != nullptr)
> +	this->invalidate (regnum);
> +    });
>   
>     target_store_registers (this, regnum);
>