[Qemu-devel] qemu-system-ppc problem with PVR access from user space

[Jason Wessel <jason.wessel@windriver.com>]

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The typical kernel + user space I boot on the prep machine no longer
boots due to an issue accessing the PVR special purpose register.  When
the PVR is accessed from user space, it should generate an exception
with the PC set to the instruction that it occurred at when it saves to
the stack.  In the latest CVS, it is off by 4 bytes.  With out the fix
/sbin/init gets killed because the kernel's trap handler which does the
userspace emulation of the instruction does not clean up the trap.

I am using the attached patch to work around the problem, but I wonder
if there is a more generic problem that was introduced as a regression
with all ppc merges in the last month or so, given this used to work
fine through the generic handler.

Any insight into this would certainly be useful.

Thanks,
Jason.

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Work around the problem that the PC register is not saved with
the right address when taking a user space PVR access exception.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 target-ppc/translate_init.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -92,6 +92,13 @@ static void spr_write_clear (void *opaqu
 }
 #endif
 
+static void spr_read_generic_fault_user(void *opaque, int sprn)
+{
+	DisasContext *ctx = opaque;
+	ctx->nip -= 4;
+	GEN_EXCP_PRIVREG(ctx);
+}
+
 /* SPR common to all PowerPC */
 /* XER */
 static void spr_read_xer (void *opaque, int sprn)
@@ -5942,7 +5949,7 @@ static void init_ppc_proc (CPUPPCState *
     /* Register SPR common to all PowerPC implementations */
     gen_spr_generic(env);
     spr_register(env, SPR_PVR, "PVR",
-                 SPR_NOACCESS, SPR_NOACCESS,
+                 &spr_read_generic_fault_user, SPR_NOACCESS,
                  &spr_read_generic, SPR_NOACCESS,
                  def->pvr);
     /* PowerPC implementation specific initialisations (SPRs, timers, ...) */