GNU C Library master sources branch roland/arm-memcpy-fix created. glibc-2.18-424-g53ec8dc

[roland at sourceware dot org]

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=53ec8dce5ba2db12c732eaf5298cd7f0589abe70

commit 53ec8dce5ba2db12c732eaf5298cd7f0589abe70
Author: Roland McGrath <roland@hack.frob.com>
Date:   Thu Nov 21 15:24:27 2013 -0800

    ARM: Fix memcpy computed-jump calculations for ARM_ALWAYS_BX case.

diff --git a/ports/ChangeLog.arm b/ports/ChangeLog.arm
index 0dfe5c7..7aa2649 100644
--- a/ports/ChangeLog.arm
+++ b/ports/ChangeLog.arm
@@ -1,3 +1,11 @@
+2013-11-21  Roland McGrath  <roland@hack.frob.com>
+
+	* sysdeps/arm/armv7/multiarch/memcpy_impl.S
+	[ARM_ALWAYS_BX] (dispatch_helper): Fix PC computation to properly
+	account for instructions after the reference to PC given that 'bx'
+	might actually be expanded to multiple instructions.
+	* sysdeps/arm/arm-features.h (ARM_BX_NINSNS): Macro removed.
+
 2013-10-30  Mike Frysinger  <vapier@gentoo.org>
 
 	* sysdeps/arm/configure.in: Moved to ...
diff --git a/ports/sysdeps/arm/arm-features.h b/ports/sysdeps/arm/arm-features.h
index 1d4b0f1..336b690 100644
--- a/ports/sysdeps/arm/arm-features.h
+++ b/ports/sysdeps/arm/arm-features.h
@@ -53,14 +53,6 @@
 # define ARM_BX_ALIGN_LOG2	2
 #endif
 
-/* The number of instructions that 'bx' expands to.  A more-specific
-   arm-features.h that defines 'bx' as a macro should define this to the
-   number instructions it expands to.  This is used only in a context
-   where the 'bx' expansion won't cross an ARM_BX_ALIGN_LOG2 boundary.  */
-#ifndef ARM_BX_NINSNS
-# define ARM_BX_NINSNS		1
-#endif
-
 /* An OS-specific arm-features.h file may define ARM_NO_INDEX_REGISTER to
    indicate that the two-register addressing modes must never be used.  */
 
diff --git a/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S b/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S
index ad43a3d..44cecb0 100644
--- a/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S
+++ b/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S
@@ -127,25 +127,26 @@
 	.purgem dispatch_step
 	.endm
 #else
-# if ARM_BX_ALIGN_LOG2 < 4
+# if ARM_BX_ALIGN_LOG2 < 3
 #  error case not handled
 # endif
 	.macro dispatch_helper steps, log2_bytes_per_step
-	.p2align ARM_BX_ALIGN_LOG2
 	/* TMP1 gets (max_bytes - bytes_to_copy), where max_bytes is
 	   (STEPS << LOG2_BYTES_PER_STEP).
-	   So this is (steps_to_skip << LOG2_BYTES_PER_STEP).  */
-	rsb	tmp1, tmp1, #(\steps << \log2_bytes_per_step)
-	/* Pad so that the add;bx pair immediately precedes an alignment
-	   boundary.  Hence, TMP1=0 will run all the steps.  */
-	.rept (1 << (ARM_BX_ALIGN_LOG2 - 2)) - (2 + ARM_BX_NINSNS)
-	nop
-	.endr
+	   So this is (steps_to_skip << LOG2_BYTES_PER_STEP).
+	   Then it needs further adjustment to compensate for the
+	   distance between the PC value taken below (0f + PC_OFS)
+	   and the first step's instructions (1f).  */
+	rsb	tmp1, tmp1, #((\steps << \log2_bytes_per_step) \
+			      + ((1f - PC_OFS - 0f) \
+				 >> (ARM_BX_ALIGN_LOG2 - \log2_bytes_per_step)))
 	/* Shifting down LOG2_BYTES_PER_STEP gives us the number of
 	   steps to skip, then shifting up ARM_BX_ALIGN_LOG2 gives us
 	   the (byte) distance to add to the PC.  */
-	add	tmp1, pc, tmp1, lsl #(ARM_BX_ALIGN_LOG2 - \log2_bytes_per_step)
+0:	add	tmp1, pc, tmp1, lsl #(ARM_BX_ALIGN_LOG2 - \log2_bytes_per_step)
 	bx	tmp1
+	.p2align ARM_BX_ALIGN_LOG2
+1:
 	.endm
 
 	.macro dispatch_7_dword

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