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Subject: Re: arm/161498: commit references a PR
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The following reply was made to PR arm/161498; it has been noted by GNATS.

From: dfilter@FreeBSD.ORG (dfilter service)
To: bug-followup@FreeBSD.org
Cc:  
Subject: Re: arm/161498: commit references a PR
Date: Sun, 16 Oct 2011 17:59:42 +0000 (UTC)

 Author: cognet
 Date: Sun Oct 16 17:59:28 2011
 New Revision: 226443
 URL: http://svn.freebsd.org/changeset/base/226443
 
 Log:
   Fix 2 bugs :
   
   - A race condition could happen if two threads were using RAS at the same time
   as the code didn't reset RAS_END, the RAS code could believe we were not in
   a RAS, when we were in fact.
   - Using signed value logic to compare addresses wasn't such a good idea.
   
   Many thanks to Ian to investigate on these issues.
   
   Pointy hat to: 	cognet
   PR:		arm/161498
   Submitted by:	Ian Lepore <freebsd At damnhippie DOT dyndns dot org
   MFC after:	1 week
 
 Modified:
   head/sys/arm/include/asmacros.h
   head/sys/arm/include/sysarch.h
 
 Modified: head/sys/arm/include/asmacros.h
 ==============================================================================
 --- head/sys/arm/include/asmacros.h	Sun Oct 16 17:38:20 2011	(r226442)
 +++ head/sys/arm/include/asmacros.h	Sun Oct 16 17:59:28 2011	(r226443)
 @@ -71,9 +71,8 @@
  	ldr	r0, =ARM_RAS_START;					   \
  	mov	r1, #0;							   \
  	str	r1, [r0];						   \
 -	ldr	r0, =ARM_RAS_END;					   \
  	mov	r1, #0xffffffff;					   \
 -	str	r1, [r0];
 +	str	r1, [r0, #4];
  
  /*
   * PULLFRAME - macro to pull a trap frame from the stack in the current mode
 @@ -120,20 +119,19 @@
  	stmia	r0, {r13-r14}^;		/* Push the user mode registers */ \
          mov     r0, r0;                 /* NOP for previous instruction */ \
  	ldr	r5, =ARM_RAS_START;	/* Check if there's any RAS */	   \
 -	ldr	r3, [r5];						   \
 -	cmp	r3, #0;			/* Is the update needed ? */	   \
 -	ldrgt	lr, [r0, #16];						   \
 -	ldrgt	r1, =ARM_RAS_END;					   \
 -	ldrgt	r4, [r1];		/* Get the end of the RAS */	   \
 -	movgt	r2, #0;			/* Reset the magic addresses */	   \
 -	strgt	r2, [r5];						   \
 -	movgt	r2, #0xffffffff;					   \
 -	strgt	r2, [r1];						   \
 -	cmpgt	lr, r3;			/* Were we in the RAS ? */	   \
 -	cmpgt	r4, lr;							   \
 -	strgt	r3, [r0, #16];		/* Yes, update the pc */	   \
 -	mrs	r0, spsr_all;		/* Put the SPSR on the stack */	   \
 -	str	r0, [sp, #-4]!
 +	ldr     r4, [r5, #4];           /* reset it to point at the     */ \
 +	cmp     r4, #0xffffffff;        /* end of memory if necessary;  */ \
 +	movne   r1, #0xffffffff;        /* leave value in r4 for later  */ \
 +	strne   r1, [r5, #4];           /* comparision against PC.      */ \
 +	ldr     r3, [r5];               /* Retrieve global RAS_START    */ \
 +	cmp     r3, #0;                 /* and reset it if non-zero.    */ \
 +	movne   r1, #0;                 /* If non-zero RAS_START and    */ \
 +	strne   r1, [r5];               /* PC was lower than RAS_END,   */ \
 +	ldrne   r1, [r0, #16];          /* adjust the saved PC so that  */ \
 +	cmpne   r4, r1;                 /* execution later resumes at   */ \
 +	strhi   r3, [r0, #16];          /* the RAS_START location.      */ \
 +	mrs     r0, spsr_all;                                              \
 +	str     r0, [sp, #-4]!
  
  /*
   * PULLFRAMEFROMSVCANDEXIT - macro to pull a trap frame from the stack
 
 Modified: head/sys/arm/include/sysarch.h
 ==============================================================================
 --- head/sys/arm/include/sysarch.h	Sun Oct 16 17:38:20 2011	(r226442)
 +++ head/sys/arm/include/sysarch.h	Sun Oct 16 17:59:28 2011	(r226443)
 @@ -42,9 +42,13 @@
   * The ARM_TP_ADDRESS points to a special purpose page, which is used as local
   * store for the ARM per-thread data and Restartable Atomic Sequences support.
   * Put it just above the "high" vectors' page.
 - * the cpu_switch() code assumes ARM_RAS_START is ARM_TP_ADDRESS + 4, and
 + * The cpu_switch() code assumes ARM_RAS_START is ARM_TP_ADDRESS + 4, and
   * ARM_RAS_END is ARM_TP_ADDRESS + 8, so if that ever changes, be sure to
   * update the cpu_switch() (and cpu_throw()) code as well.
 + * In addition, code in arm/include/atomic.h and arm/include/asmacros.h
 + * assumes that ARM_RAS_END is at ARM_RAS_START+4, so be sure to update those
 + * if ARM_RAS_END moves in relation to ARM_RAS_START (look for occurrances
 + * of ldr/str rm,[rn, #4]).
   */
  #define ARM_TP_ADDRESS		(ARM_VECTORS_HIGH + 0x1000)
  #define ARM_RAS_START		(ARM_TP_ADDRESS + 4)
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