[PATCH] Fix Cell debugging regression (Re: [PATCH] Use thread_info and inferior pointers more throughout)

[Pedro Alves <palves at redhat dot com>]

On 06/27/2018 12:33 PM, Ulrich Weigand wrote:
> Pedro Alves wrote:
> 
>>  ps_err_e
>>  ps_lgetregs (struct ps_prochandle *ph, lwpid_t lwpid, prgregset_t gregset)
>>  {
>> -  ptid_t ptid = ptid_build (ptid_get_pid (ph->ptid), lwpid, 0);
>> -  struct regcache *regcache
>> -    = get_thread_arch_regcache (ptid, target_gdbarch ());
>> +  struct regcache *regcache = get_thread_regcache (ph->thread);
> 
> This change (and the related ones in the following routines
> completely break Cell multi-arch debugging.  The point of using
> get_thread_arch_regcache with target_gdbarch() instead of just
> plain get_thread_regcache is that the proc-service routines
> must always operated on the "main" (in this case PowerPC)
> architecture, because that's the register set libthread_db
> expects to be using.
> The change above switches the behavior to use the SPU architecture
> if GDB happens to interrupt SPU code.  This is wrong and causes
> internal GDB errors pretty much instantly when starting an SPU ...
Sorry, missed that.  Some comments here would be helpful.

I think this should fix it.  WDYT?

>From d4b27737d93f466955a34c89a3f304bf4d3579d2 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Wed, 27 Jun 2018 12:54:50 +0100
Subject: [PATCH] Fix Cell debugging regression

Commit 00431a78b28f ("Use thread_info and inferior pointers more
throughout") broke Cell multi-arch debugging, because it made the
proc-service routines (ps_lgetregs etc.) access registers using the
SPU architecture if GDB happens to interrupt SPU code.  The
proc-service routines must always operate on the "main" (in this case
PowerPC) architecture, because that's the register set libthread_db
expects to be using.

Restore the previous behavior, but wrapped in a new
get_thread_main_regcache function with a describing comment hinting at
multi-arch scenarios.

gdb/ChangeLog:
2018-06-27  Pedro Alves  <palves@redhat.com>

	* proc-service.c (ps_lgetregs, ps_lsetregs, ps_lgetfpregs)
	(ps_lsetfpregs): Use get_thread_main_regcache.
	* regcache.c (get_thread_main_regcache): Define.
	* regcache.h (get_thread_main_regcache): Declare.
---
 gdb/proc-service.c | 14 ++++++++++----
 gdb/regcache.c     |  8 ++++++++
 gdb/regcache.h     |  8 ++++++++
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/gdb/proc-service.c b/gdb/proc-service.c
index 04867d227b..d96a689490 100644
--- a/gdb/proc-service.c
+++ b/gdb/proc-service.c
@@ -126,13 +126,19 @@ ps_pdwrite (struct ps_prochandle *ph, psaddr_t addr,
   return ps_xfer_memory (ph, addr, (gdb_byte *) buf, size, 1);
 }
 
+/* The following register-related routines use
+   get_thread_main_regcache instead of get_thread_regcache because in
+   Cell debugging, the proc-service routines must always operate on
+   the "main" (in this case PowerPC) architecture, because that's the
+   register set libthread_db expects to be using.  */
+
 /* Get the general registers of LWP LWPID within the target process PH
    and store them in GREGSET.  */
 
 ps_err_e
 ps_lgetregs (struct ps_prochandle *ph, lwpid_t lwpid, prgregset_t gregset)
 {
-  struct regcache *regcache = get_thread_regcache (ph->thread);
+  struct regcache *regcache = get_thread_main_regcache (ph->thread);
 
   target_fetch_registers (regcache, -1);
   fill_gregset (regcache, (gdb_gregset_t *) gregset, -1);
@@ -146,7 +152,7 @@ ps_lgetregs (struct ps_prochandle *ph, lwpid_t lwpid, prgregset_t gregset)
 ps_err_e
 ps_lsetregs (struct ps_prochandle *ph, lwpid_t lwpid, const prgregset_t gregset)
 {
-  struct regcache *regcache = get_thread_regcache (ph->thread);
+  struct regcache *regcache = get_thread_main_regcache (ph->thread);
 
   supply_gregset (regcache, (const gdb_gregset_t *) gregset);
   target_store_registers (regcache, -1);
@@ -160,7 +166,7 @@ ps_lsetregs (struct ps_prochandle *ph, lwpid_t lwpid, const prgregset_t gregset)
 ps_err_e
 ps_lgetfpregs (struct ps_prochandle *ph, lwpid_t lwpid, gdb_prfpregset_t *fpregset)
 {
-  struct regcache *regcache = get_thread_regcache (ph->thread);
+  struct regcache *regcache = get_thread_main_regcache (ph->thread);
 
   target_fetch_registers (regcache, -1);
   fill_fpregset (regcache, (gdb_fpregset_t *) fpregset, -1);
@@ -175,7 +181,7 @@ ps_err_e
 ps_lsetfpregs (struct ps_prochandle *ph, lwpid_t lwpid,
 	       const gdb_prfpregset_t *fpregset)
 {
-  struct regcache *regcache = get_thread_regcache (ph->thread);
+  struct regcache *regcache = get_thread_main_regcache (ph->thread);
 
   supply_fpregset (regcache, (const gdb_fpregset_t *) fpregset);
   target_store_registers (regcache, -1);
diff --git a/gdb/regcache.c b/gdb/regcache.c
index 1bc4f0de88..6380f3cbea 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -399,6 +399,14 @@ get_thread_regcache (thread_info *thread)
   return get_thread_regcache (thread->ptid);
 }
 
+/* See regcache.h.  */
+
+struct regcache *
+get_thread_main_regcache (thread_info *thread)
+{
+  return get_thread_arch_regcache (thread->ptid, thread->inf->gdbarch);
+}
+
 struct regcache *
 get_current_regcache (void)
 {
diff --git a/gdb/regcache.h b/gdb/regcache.h
index 983137f6ad..efeb29c1bd 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -34,6 +34,14 @@ extern struct regcache *get_thread_regcache (ptid_t ptid);
 /* Get the regcache of THREAD.  */
 extern struct regcache *get_thread_regcache (thread_info *thread);
 
+/* Get the thread's regcache using its inferior's "main" architecture.
+   In multi-arch debugging scenarios, the thread's architecture may
+   differ from the inferior's "main" architecture.  E.g., in the Cell
+   combined debugger, if GDB happens to interrupt SPU code, the
+   thread's architecture is SPU, and the main architecture is
+   PowerPC.  */
+extern struct regcache *get_thread_main_regcache (thread_info *thread);
+
 extern struct regcache *get_thread_arch_regcache (ptid_t, struct gdbarch *);
 extern struct regcache *get_thread_arch_aspace_regcache (ptid_t,
 							 struct gdbarch *,
-- 
2.14.4