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Re: [PATCH] MIPS: microMIPS: Redefine value of BRK_BUG.

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [PATCH] MIPS: microMIPS: Redefine value of BRK_BUG.
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 17 Jan 2013 23:54:10 +0100
Cc: "Steven J. Hill" <sjhill@mips.com>, linux-mips@linux-mips.org
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On Thu, Jan 17, 2013 at 10:15:49AM -0800, David Daney wrote:

> >diff --git a/arch/mips/include/asm/break.h b/arch/mips/include/asm/break.h
> >index 9161e68..df9d090 100644
> >--- a/arch/mips/include/asm/break.h
> >+++ b/arch/mips/include/asm/break.h
> >@@ -27,6 +27,7 @@
> >  #define BRK_STACKOVERFLOW 9        /* For Ada stackchecking */
> >  #define BRK_NORLD  10      /* No rld found - not used by Linux/MIPS */
> >  #define _BRK_THREADBP      11      /* For threads, user bp (used by 
> > debuggers) */
> >+#define BRK_BUG_MM  12      /* Used by BUG() in microMIPS mode */
> >  #define BRK_BUG            512     /* Used by BUG() */
> 
> Can we move the CONFIG_CPU_MICROMIPS to here and just call the thing
> BRK_BUG?
> 
> Or perhaps redefining it unconditionally.  I am not sure what the
> implications of doing that would be.
> 
> That way...

The kernel decodes break and trap instruction in traps.c.  For a microMIPS-
enabled kernel it needs to be able to decode both classic and microMIPS
encoded instructions so we want separate symbols.

Or we do something like

#define BRK_MM_BUG       12      /* Used by BUG() in microMIPS mode */
#define BRK_CM_BUG      512     /* Used by BUG() */

#ifdef __mips_micromips
#define BRK_BUG         BRK_MM_BUG
#else
#define BRK_BUG         BRK_CM_BUG
#endif

This makes the BRK_MM_* / BRK_CM_* macros available for decoding instructions
and the microMIPS-agnostic BRK_BUG for code such as BUG().

> >  #define BRK_KDB            513     /* Used in KDB_ENTER() */
> >  #define BRK_MEMU   514     /* Used by FPU emulator */
> >diff --git a/arch/mips/include/asm/bug.h b/arch/mips/include/asm/bug.h
> >index 540c98a..b716fb9 100644
> >--- a/arch/mips/include/asm/bug.h
> >+++ b/arch/mips/include/asm/bug.h
> >@@ -7,6 +7,10 @@
> >  #ifdef CONFIG_BUG
> >
> >  #include <asm/break.h>
> >+#ifdef CONFIG_CPU_MICROMIPS
> >+#undef BRK_BUG
> >+#define BRK_BUG             BRK_BUG_MM
> >+#endif
> >
> 
> ...We don't need this bit.   Doing an #undef risks using different
> values for BRK_BUG depending on whether or not asm/bug.h is
> included.

And generally is not very elegant.

  Ralf

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