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[PATCH roland/arm-atomic-warn] Fiddle ARM atomic.h to avoid -Wvolatile-register-var warnings.
- From: Roland McGrath <roland at hack dot frob dot com>
- To: libc-ports at sourceware dot org
- Date: Wed, 8 Aug 2012 13:44:42 -0700 (PDT)
- Subject: [PATCH roland/arm-atomic-warn] Fiddle ARM atomic.h to avoid -Wvolatile-register-var warnings.
Trunk GCC has -Wvolatile-register-var on by default and this hits in
some atomic.h macros because __typeof (*ptr) is leaking volatile-ness
into the non-pointer declarations and being treated as 'register volatile'.
I only did a basic compile test (with trunk gcc for arm-linux-gnueabi).
I looked at one file where I'd been getting the warning (nptl-init.c)
and the generated code differed only in reordering a couple of (non-atomic)
loads whose order shouldn't matter.
Ok?
Thanks,
Roland
ports/ChangeLog.arm
* sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h
[!__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4]
(__arch_compare_and_exchange_val_32_acq): Use uint32_t rather than
__typeof (...) for non-pointer variables derived from the arguments.
diff --git a/ports/sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h b/ports/sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h
index 4e810a2..c9ad50d 100644
--- a/ports/sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h
+++ b/ports/sysdeps/unix/sysv/linux/arm/nptl/bits/atomic.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+/* Copyright (C) 2002-2012 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
@@ -74,17 +74,24 @@ void __arm_link_error (void);
/* It doesn't matter what register is used for a_oldval2, but we must
specify one to work around GCC PR rtl-optimization/21223. Otherwise
- it may cause a_oldval or a_tmp to be moved to a different register. */
+ it may cause a_oldval or a_tmp to be moved to a different register.
+ We use the union trick rather than simply using __typeof (...) in the
+ declarations of A_OLDVAL et al because when NEWVAL or OLDVAL is of the
+ form *PTR and PTR has a 'volatile ... *' type, then __typeof (*PTR) has
+ a 'volatile ...' type and this triggers -Wvolatile-register-var to
+ complain about 'register volatile ... asm ("reg")'. */
#elif defined __thumb2__
/* Thumb-2 has ldrex/strex. However it does not have barrier instructions,
so we still need to use the kernel helper. */
#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \
- ({ register __typeof (oldval) a_oldval asm ("r0"); \
- register __typeof (oldval) a_newval asm ("r1") = (newval); \
+ ({ union { __typeof (oldval) a; uint32_t v; } oldval_arg = { .a = (oldval) };\
+ union { __typeof (newval) a; uint32_t v; } newval_arg = { .a = (newval) };\
+ register uint32_t a_oldval asm ("r0"); \
+ register uint32_t a_newval asm ("r1") = newval_arg.v; \
register __typeof (mem) a_ptr asm ("r2") = (mem); \
- register __typeof (oldval) a_tmp asm ("r3"); \
- register __typeof (oldval) a_oldval2 asm ("r4") = (oldval); \
+ register uint32_t a_tmp asm ("r3"); \
+ register uint32_t a_oldval2 asm ("r4") = oldval_arg.v; \
__asm__ __volatile__ \
("0:\tldr\t%[tmp],[%[ptr]]\n\t" \
"cmp\t%[tmp], %[old2]\n\t" \
@@ -100,14 +107,16 @@ void __arm_link_error (void);
: [new] "r" (a_newval), [ptr] "r" (a_ptr), \
[old2] "r" (a_oldval2) \
: "ip", "lr", "cc", "memory"); \
- a_tmp; })
+ (__typeof (oldval)) a_tmp; })
#else
-#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \
- ({ register __typeof (oldval) a_oldval asm ("r0"); \
- register __typeof (oldval) a_newval asm ("r1") = (newval); \
+#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \
+ ({ union { __typeof (oldval) a; uint32_t v; } oldval_arg = { .a = (oldval) };\
+ union { __typeof (newval) a; uint32_t v; } newval_arg = { .a = (newval) };\
+ register uint32_t a_oldval asm ("r0"); \
+ register uint32_t a_newval asm ("r1") = newval_arg.v; \
register __typeof (mem) a_ptr asm ("r2") = (mem); \
- register __typeof (oldval) a_tmp asm ("r3"); \
- register __typeof (oldval) a_oldval2 asm ("r4") = (oldval); \
+ register uint32_t a_tmp asm ("r3"); \
+ register uint32_t a_oldval2 asm ("r4") = oldval_arg.v; \
__asm__ __volatile__ \
("0:\tldr\t%[tmp],[%[ptr]]\n\t" \
"cmp\t%[tmp], %[old2]\n\t" \
@@ -123,7 +132,7 @@ void __arm_link_error (void);
: [new] "r" (a_newval), [ptr] "r" (a_ptr), \
[old2] "r" (a_oldval2) \
: "ip", "lr", "cc", "memory"); \
- a_tmp; })
+ (__typeof (oldval)) a_tmp; })
#endif
#define __arch_compare_and_exchange_val_64_acq(mem, newval, oldval) \