Re: Atari TT (next)

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On Mon, Jan 9, 2012 at 11:40, Andreas Schwab <schwab@xxxxxxxxxxxxxx> wrote:
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

Thanks!

Tuomas: I think this will fix your problem, too?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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