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From: Helge Deller <deller@gmx.de>
To: linux-parisc@vger.kernel.org,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	John David Anglin <dave.anglin@bell.net>
Subject: [PATCH] parisc: Prevent using same register as soure and target in extru/shr
Date: Tue, 17 May 2022 14:49:15 +0200	[thread overview]
Message-ID: <YoOZy3A3R0i0DUWB@p100> (raw)

In 2004 Randolph added the shr() assembly macro and noted that the
source and target register could not be the same.

I did not find any confindence in the docs for this restriction. Maybe
it's related that on PA2.0 the upper bits may be clobbered?

Anyway, add a compile-time check for it now.

Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/include/asm/assembly.h b/arch/parisc/include/asm/assembly.h
index ea0cb318b13d..ca1a12ae5ee7 100644
--- a/arch/parisc/include/asm/assembly.h
+++ b/arch/parisc/include/asm/assembly.h
@@ -146,6 +146,9 @@
 	/* Shift Right - note the r and t can NOT be the same! */
 	.macro shr r, sa, t
 	extru \r, 31-(\sa), 32-(\sa), \t
+.ifc \r,\t
+        .error "Can not used the same register (\r) in shr/extru as source and target register."
+.endif
 	.endm

 	/* pa20w version of shift right */

             reply	other threads:[~2022-05-17 12:49 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-17 12:49 Helge Deller [this message]
2022-05-17 12:54 ` [PATCH] parisc: Prevent using same register as soure and target in extru/shr Helge Deller
2022-05-17 13:41   ` John David Anglin
2022-05-18  6:57   ` Sven Schnelle
2022-05-18  7:10     ` Helge Deller

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