On 2017/06/22 01:48PM, Nicholas Piggin wrote:

On Thu, 22 Jun 2017 00:08:42 +0530
"Naveen N. Rao" [off-list ref] wrote:

quoted

We can't take traps with relocation off, so blacklist enter_rtas() and
rtas_return_loc(). However, instead of blacklisting all of enter_rtas(),
introduce a new symbol __enter_rtas from where on we can't take a trap
and blacklist that.

Signed-off-by: Naveen N. Rao <redacted>
---
 arch/powerpc/kernel/entry_64.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index d376f07153d7..49c35450f399 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S

@@ -1076,6 +1076,8 @@ _GLOBAL(enter_rtas)
         rldicr  r9,r9,MSR_SF_LG,(63-MSR_SF_LG)
 	ori	r9,r9,MSR_IR|MSR_DR|MSR_FE0|MSR_FE1|MSR_FP|MSR_RI|MSR_LE
 	andc	r6,r0,r9
+
+__enter_rtas:
 	sync				/* disable interrupts so SRR0/1 */
 	mtmsrd	r0			/* don't get trashed */

Along the lines of the system call patch... For consistency, could we
put the __enter_rtas right after mtmsrd? And I wonder if we shoul

Sure.

come up with a common prefix or postfix naming convention for these
such labels used to control probing?

We could, but I am not sure it will help much. On the other hand, such 
symbols may make backtraces pretty distracting.

I'm just using '__' as a prefix to make it less distracting, though it 
isn't all that great either. I'm clearly hopeless with names o_O

The other option is to just blacklist entire functions, but we will then 
lose the ability to probe in many places where we may have wanted to.

How do opal calls avoid tracing?

It doesn't yet. I'm still going through the initial few symbols and 
identifying what needs blacklisting. Opal is further down.

Thanks,
Naveen