Re: [PATCH] powerpc/64s: power4 nap fixup in C

On Mär 29 2021, Andreas Schwab wrote:

On Mär 29 2021, Christophe Leroy wrote:

quoted

Le 29/03/2021 à 10:33, Benjamin Herrenschmidt a écrit :

quoted

On Fri, 2021-03-12 at 11:20 +1000, Nicholas Piggin wrote:

quoted

+static inline void nap_adjust_return(struct pt_regs *regs)

+{

+#ifdef CONFIG_PPC_970_NAP

+       if (unlikely(test_thread_local_flags(_TLF_NAPPING))) {
+               /* Can avoid a test-and-clear because NMIs do not call this */
+               clear_thread_local_flags(_TLF_NAPPING);
+               regs->nip = (unsigned long)power4_idle_nap_return;
+       }

Is this a pointer to a function descriptor or the actual code ?

--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S

@@ -209,4 +209,8 @@ _GLOBAL(power4_idle_nap)
 	mtmsrd	r7
 	isync
 	b	1b
+
+	.globl power4_idle_nap_return
+power4_idle_nap_return:
+	blr
 #endif

The problem is not the definition, it is the reference.  In C, a
function symbol always resolves to the address of the descriptor.

Sorry, this is wrong, I have misremembered how function descriptors work
on ppc64.  The address is really pointing to the actual code.

Andreas.

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Andreas Schwab, schwab@linux-m68k.org
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