Patchwork [RFC,v5,3/9] Add scoped_restore_regcache_ptid

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Submitter Philipp Rudo
Date March 12, 2018, 3:31 p.m.
Message ID <20180312153115.47321-4-prudo@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/26286/
State New
Headers show

Comments

Philipp Rudo - March 12, 2018, 3:31 p.m.
When a target and its target beneath use different ptids to identify a
thread the regcaches ptid has to be set/restored when calls are passed down
to the target beneath to e.g. fetch_registers.  Add a scoped_restore to
simplify this.

gdb/ChangeLog:

	regcache.h (scoped_restore_regcache_ptid): New class.
---
 gdb/regcache.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
Simon Marchi - March 17, 2018, 6:08 p.m.
On 2018-03-12 11:31 AM, Philipp Rudo wrote:
> When a target and its target beneath use different ptids to identify a
> thread the regcaches ptid has to be set/restored when calls are passed down
> to the target beneath to e.g. fetch_registers.  Add a scoped_restore to
> simplify this.

Though I don't understand yet why this is needed (I'll find out when reading
the following patches), the implementation looks ok.

I don't think this is an issue (at least for now), but there is this observer
"thread_ptid_changed" that indicates when a thread changes ptid.  If this
observer is triggered while we have temporarily changed a regcache's ptid,
I guess we could miss updating a regcache's ptid, as
scoped_restore_regcache_ptid will reset it to the old ptid.  It's probably
not a problem but I think it's good to be aware of this.

Simon

Patch

diff --git a/gdb/regcache.h b/gdb/regcache.h
index d7bb8b5c93..8e45d7c513 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -403,6 +403,27 @@  private:
   registers_changed_ptid (ptid_t ptid);
 };
 
+/* Save/restore the current ptid of REGCACHE.  */
+
+class scoped_restore_regcache_ptid
+{
+public:
+  scoped_restore_regcache_ptid (regcache *regcache)
+    : m_regcache (regcache), m_ptid (regcache->ptid ())
+  {}
+
+  ~scoped_restore_regcache_ptid ()
+    {
+      m_regcache->set_ptid (m_ptid);
+    }
+
+  DISABLE_COPY_AND_ASSIGN (scoped_restore_regcache_ptid);
+
+private:
+  regcache *m_regcache;
+  ptid_t m_ptid;
+};
+
 class readonly_detached_regcache : public readable_regcache
 {
 public: