[v2] Fix Cell debugging regression (Re: [PATCH] Use thread_info and inferior pointers more throughout)
Commit Message
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(-)
@@ -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);