[PATCH v2] Fix Cell debugging regression (Re: [PATCH] Use thread_info and inferior pointers more throughout)

[Pedro Alves <palves@redhat.com>]

On 06/27/2018 02:17 PM, Pedro Alves wrote:
> On 06/27/2018 02:12 PM, Ulrich Weigand wrote:

>> In the meantime I also noticed another potential issue (which is
>> not related to multi-arch at all):
>>
>>>  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 also assumes that ph->thread is the same thread
>> as the one indicated by lwpid.  Looking at the callers of the
>> various libthread_db routines that might result in a callback
>> to the ps_...regs routines, it is not immediately obvious to
>> me that this is actually true.  Are you sure this can never
>> be called to look up registers of another thread?
> 
> Argh, no, I completely missed that.  Let me take a better look.

Just OOC, I added a assertion like
   gdb_assert (lwpid == ph->thread->ptid.lwp ());
and it didn't trigger on x86-64, I think because libthread_db
on x86-64 uses ps_get_thread_area and doesn't call into these
routines.  Maybe it does in some cases, like core debugging.
I didn't run the whole testsuite, only a couple threaded programs.

Anyways, the assertion did fail on PowerPC.

Here's a new version that fixes that too.  WDYT?

From 66b0ff00aca764636e681392b60aacc64343ec21 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_ps_regcache function with a describing comment.

Also, the ps_l*regs routines have an explicit lwpid parameter that
said commit missed; with the commit mentioned above, we started always
reading the registers off of the current thread, which is incorrect.
That is fixed by this commit too.

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

	* proc-service.c (get_ps_regcache): New.
	(ps_lgetregs, ps_lsetregs, ps_lgetfpregs)
	(ps_lsetfpregs): Use it.
---
 gdb/proc-service.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/gdb/proc-service.c b/gdb/proc-service.c
index 04867d227b..393cd90927 100644
--- a/gdb/proc-service.c
+++ b/gdb/proc-service.c
@@ -126,13 +126,28 @@ ps_pdwrite (struct ps_prochandle *ph, psaddr_t addr,
   return ps_xfer_memory (ph, addr, (gdb_byte *) buf, size, 1);
 }
 
+/* Get a regcache for LWPID using its inferior's "main" architecture,
+   which is the register set libthread_db expects to be using.  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.  */
+
+static struct regcache *
+get_ps_regcache (struct ps_prochandle *ph, lwpid_t lwpid)
+{
+  inferior *inf = ph->thread->inf;
+  return get_thread_arch_regcache (ptid_t (inf->pid, lwpid), inf->gdbarch);
+}
+
 /* 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_ps_regcache (ph, lwpid);
 
   target_fetch_registers (regcache, -1);
   fill_gregset (regcache, (gdb_gregset_t *) gregset, -1);
@@ -146,7 +161,7 @@ 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_ps_regcache (ph, lwpid);
 
   supply_gregset (regcache, (const gdb_gregset_t *) gregset);
   target_store_registers (regcache, -1);
@@ -160,7 +175,7 @@ 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_ps_regcache (ph, lwpid);
 
   target_fetch_registers (regcache, -1);
   fill_fpregset (regcache, (gdb_fpregset_t *) fpregset, -1);
@@ -175,7 +190,7 @@ 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_ps_regcache (ph, lwpid);
 
   supply_fpregset (regcache, (const gdb_fpregset_t *) fpregset);
   target_store_registers (regcache, -1);
-- 
2.14.4