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Re: Breaking ARM's mcount implementations into a separate file


Hello!

On 2009-12-15 13:55, Joseph S. Myers wrote:
> On Tue, 15 Dec 2009, Thomas Schwinge wrote:
>> On 2009-12-15 02:05, Joseph S. Myers wrote:
>> > I'm not sure of the significance of having separate ARM/Thumb versions, 
>> 
>> Well, if I understand this correctly, it was you, together with Paul
>> Brook, who have added this code on 2009-02-05.
>
> You need to look more carefully at the history before I merged Thumb-2 
> support from EGLIBC to FSF ports.  The new mcount entry point dates back 
> at least to <http://www.eglibc.org/archives/patches/msg00449.html> and 
> other discussions around that time, while Thumb-2 mcount comes from 
> <http://www.eglibc.org/archives/patches/msg00143.html>.  I.e., on 
> 2009-02-05 I merged existing code without knowing the significance of 
> every bit of it.

Thanks for the clarification.  I had simply been looking at ChangeLog.arm
which contains this:

2009-02-05  Paul Brook  <paul@codesourcery.com>
	    Joseph Myers  <joseph@codesourcery.com>

	[...]
	* sysdeps/arm/machine-gmon.h (MCOUNT): Add Thumb-2 implementation.
	[...]

..., so I supposed that you had been directly involved with that.


> You'll need to send the patch in a form appropriate for committing, tested 
> as both ARM and Thumb-2.

Thusly done with the following patch.

I folded the two _mcount definitions into one -- but that one now
consists of nearly an equal amount of CPP conditionals compared to
assembly instructions, so if you'd rather have a bit of assembly source
code duplication, but better readability (?), then please tell and I'll
modify accordingly.


2009-12-15  Thomas Schwinge  <thomas@codesourcery.com>

	* sysdeps/arm/eabi/Makefile [gmon] (sysdep_routines): Add arm-mcount.
	* sysdeps/arm/eabi/machine-gmon.h (mcount_internal): Define to
	`__mcount_internal'.
	(MCOUNT (__gnu_mcount_nc), OLD_MCOUNT (_mcount), mcount): Move to...
	* sysdeps/arm/eabi/arm-mcount.S: ... this new file as __gnu_mcount_nc,
	_mcount, and mcount, respectively.

diff --git a/glibc-ports-mainline/sysdeps/arm/eabi/Makefile b/glibc-ports-mainline/sysdeps/arm/eabi/Makefile
index 36ddb8e..73185cb 100644
--- a/glibc-ports-mainline/sysdeps/arm/eabi/Makefile
+++ b/glibc-ports-mainline/sysdeps/arm/eabi/Makefile
@@ -15,6 +15,10 @@ static-only-routines += $(aeabi_constants)
 gen-as-const-headers += rtld-global-offsets.sym
 endif
 
+ifeq ($(subdir),gmon)
+sysdep_routines += arm-mcount
+endif
+
 ifeq ($(subdir),debug)
 CFLAGS-backtrace.c += -funwind-tables
 CFLAGS-tst-backtrace2.c += -funwind-tables
diff --git a/glibc-ports-mainline/sysdeps/arm/eabi/arm-mcount.S b/glibc-ports-mainline/sysdeps/arm/eabi/arm-mcount.S
new file mode 100644
index 0000000..2aa50b7
--- /dev/null
+++ b/glibc-ports-mainline/sysdeps/arm/eabi/arm-mcount.S
@@ -0,0 +1,83 @@
+/* Implementation of profiling support.  ARM EABI version.
+   Copyright (C) 2008, 2009 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+/* Don't call mcount when calling mcount...  */
+#undef PROF
+
+#include <sysdep.h>
+
+
+#ifdef __thumb2__
+	.thumb
+	.syntax unified
+#endif
+
+
+/* Use an assembly stub with a special ABI.  The calling lr has been
+   pushed to the stack (which will be misaligned).  We should preserve
+   all registers except ip and pop a word off the stack.
+
+   NOTE: This assumes mcount_internal does not clobber any non-core
+   (coprocessor) registers.  Currently this is true, but may require
+   additional attention in the future.
+
+   The calling sequence looks something like:
+func:
+   push {lr}
+   bl __gnu_mount_nc
+   <function body>
+*/
+
+ENTRY(__gnu_mcount_nc)
+	push {r0, r1, r2, r3, lr}
+	bic r1, lr, #1
+	ldr r0, [sp, #20]
+	bl __mcount_internal
+	pop {r0, r1, r2, r3, ip, lr}
+	bx ip
+END(__gnu_mcount_nc)
+
+
+/* Provide old mcount for backwards compatibility.  This requires
+   code be compiled with APCS frame pointers.  */
+
+ENTRY(_mcount)
+	stmdb sp!, {r0, r1, r2, r3, fp, lr}
+#ifdef __thumb2__
+	movs r0, fp
+	ittt ne
+	ldrne r0, [r0, #-4]
+#else
+	movs fp, fp
+	ldrne r0, [fp, #-4]
+#endif
+	movnes r1, lr
+	blne __mcount_internal
+#ifdef __thumb2__
+	ldmia sp!, {r0, r1, r2, r3, fp, pc}
+#else
+	ldmia sp!, {r0, r1, r2, r3, fp, lr}
+	bx lr
+#endif
+END(_mcount)
+
+/* The canonical name for the function is `_mcount' in both C and asm,
+   but some old asm code might assume it's `mcount'.  */
+#undef mcount
+weak_alias (_mcount, mcount)
diff --git a/glibc-ports-mainline/sysdeps/arm/eabi/machine-gmon.h b/glibc-ports-mainline/sysdeps/arm/eabi/machine-gmon.h
index 189a9a3..aca23c9 100644
--- a/glibc-ports-mainline/sysdeps/arm/eabi/machine-gmon.h
+++ b/glibc-ports-mainline/sysdeps/arm/eabi/machine-gmon.h
@@ -1,5 +1,5 @@
 /* Machine-dependent definitions for profiling support.  ARM EABI version.
-   Copyright (C) 2008 Free Software Foundation, Inc.
+   Copyright (C) 2008, 2009 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -17,83 +17,18 @@
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */
 
+#include <sysdep.h>
+
 /* GCC for the ARM cannot compile __builtin_return_address(N) for N != 0, 
    so we must use an assembly stub.  */
 
-#include <sysdep.h>
-static void mcount_internal (u_long frompc, u_long selfpc) __attribute_used__;
+/* We must not pollute the global namespace.  */
+#define mcount_internal __mcount_internal
 
+extern void mcount_internal (u_long frompc, u_long selfpc) internal_function;
 #define _MCOUNT_DECL(frompc, selfpc) \
-static void mcount_internal (u_long frompc, u_long selfpc)
-
-/* Use an assembly stub with a special ABI.  The calling lr has been
-   pushed to the stack (which will be misaligned).  We should preserve
-   all registers except ip and pop a word off the stack.
-
-   NOTE: This assumes mcount_internal does not clobber any non-core
-   (coprocessor) registers.  Currently this is true, but may require
-   additional attention in the future.
-
-   The calling sequence looks something like:
-func:
-   push {lr}
-   bl __gnu_mount_nc
-   <function body>
- */
-
-
-#define MCOUNT								\
-void __attribute__((__naked__)) __gnu_mcount_nc(void)			\
-{									\
-    asm ("push {r0, r1, r2, r3, lr}\n\t"				\
-	 "bic r1, lr, #1\n\t"						\
-	 "ldr r0, [sp, #20]\n\t"					\
-	 "bl mcount_internal\n\t"					\
-	 "pop {r0, r1, r2, r3, ip, lr}\n\t"				\
-	 "bx ip");							\
-}									\
-OLD_MCOUNT
-
-/* Provide old mcount for backwards compatibility.  This requires
-   code be compiled with APCS frame pointers.  */
-
-#ifndef NO_UNDERSCORES
-/* The asm symbols for C functions are `_function'.
-   The canonical name for the counter function is `mcount', no _.  */
-void _mcount (void) asm ("mcount");
-#else
-/* The canonical name for the function is `_mcount' in both C and asm,
-   but some old asm code might assume it's `mcount'.  */
-void _mcount (void);
-weak_alias (_mcount, mcount)
-#endif
-
-#ifdef __thumb2__
-
-#define OLD_MCOUNT							\
-void __attribute__((__naked__)) _mcount (void)				\
-{									\
-  __asm__("push		{r0, r1, r2, r3, fp, lr};"			\
-	  "movs		r0, fp;"					\
-	  "ittt		ne;"						\
-	  "ldrne	r0, [r0, #-4];"					\
-	  "movsne	r1, lr;"					\
-	  "blne		mcount_internal;"				\
-	  "pop		{r0, r1, r2, r3, fp, pc}");			\
-}
-
-#else
+  void internal_function mcount_internal (u_long frompc, u_long selfpc)
 
-#define OLD_MCOUNT							\
-void __attribute__((__naked__)) _mcount (void)				\
-{									\
-  __asm__("stmdb	sp!, {r0, r1, r2, r3, fp, lr};"			\
-	  "movs		fp, fp;"					\
-	  "ldrne	r0, [fp, #-4];"					\
-	  "movnes	r1, lr;"					\
-	  "blne		mcount_internal;"				\
-	  "ldmia	sp!, {r0, r1, r2, r3, fp, lr};"			\
-	  "bx		lr");						\
-}
 
-#endif
+/* Define MCOUNT as empty since we have the implementation in another file.  */
+#define MCOUNT


Regards,
 Thomas

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