Re: Atari TT (next)

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Alan Hourihane <alanh@xxxxxxxxxxxxxx> writes:

*** FORMAT ERROR ***   FORMAT=0
Current process id is 768
BAD KERNEL TRAP: 00000000
Modules linked in:
PC: [<000029de>] flush_thread+0x8/0xe

void flush_thread(void)
{
	unsigned long zero = 0;

	current->thread.fs = __USER_DS;
	if (!FPU_IS_EMU)
		asm volatile (".chip 68k/68881\n\t"
			      "frestore %0@\n\t"
			      ".chip 68k" : : "a" (&zero));
}

GCC is optimizing away the initialisation of zero, since nothing visible
is using its value.

Andreas.

--------------------------->8----------------------------------------
From bbf7451db90fcec5eade9d8bc913b78829192b9c Mon Sep 17 00:00:00 2001
From: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
Date: Mon, 9 Jan 2012 11:36:18 +0100
Subject: [PATCH] m68k: fix assembler constraint to prevent overeager gcc
 optimisation

Passing the address of a variable as an operand to an asm statement
doesn't mark the value of this variable as used, so gcc optimized its
initialisation away.  Fix this by using a "m" constraint instead.
---
 arch/m68k/kernel/process_mm.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/m68k/kernel/process_mm.c b/arch/m68k/kernel/process_mm.c
index 1bc223a..aa4ffb8 100644
--- a/arch/m68k/kernel/process_mm.c
+++ b/arch/m68k/kernel/process_mm.c
@@ -189,8 +189,8 @@ void flush_thread(void)
 	current->thread.fs = __USER_DS;
 	if (!FPU_IS_EMU)
 		asm volatile (".chip 68k/68881\n\t"
-			      "frestore %0@\n\t"
-			      ".chip 68k" : : "a" (&zero));
+			      "frestore %0\n\t"
+			      ".chip 68k" : : "m" (zero));
 }
 
 /*
-- 
1.7.8.3


-- 
Andreas Schwab, schwab@xxxxxxxxxxxxxx
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"And now for something completely different."
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