Date: Thu, 15 Dec 2011 19:42:25 +0000 (UTC) From: Dimitry Andric <dim@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r228536 - in head/lib/libthr/arch: amd64/include i386/include Message-ID: <201112151942.pBFJgPPk067323@svn.freebsd.org>
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Author: dim Date: Thu Dec 15 19:42:25 2011 New Revision: 228536 URL: http://svn.freebsd.org/changeset/base/228536 Log: The TCB_GET32() and TCB_GET64() macros in the i386 and amd64-specific versions of pthread_md.h have a special case of dereferencing a null pointer. Clang warns about this with: In file included from lib/libthr/arch/i386/i386/pthread_md.c:36: lib/libthr/arch/i386/include/pthread_md.h:96:10: error: indirection of non-volatile null pointer will be deleted, not trap [-Werror,-Wnull-dereference] return (TCB_GET32(tcb_self)); ^~~~~~~~~~~~~~~~~~~ lib/libthr/arch/i386/include/pthread_md.h:73:13: note: expanded from: : "m" (*(u_int *)(__tcb_offset(name)))); \ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ lib/libthr/arch/i386/include/pthread_md.h:96:10: note: consider using __builtin_trap() or qualifying pointer with 'volatile' Since this indirection is done relative to the fs or gs segment, to retrieve thread-specific data, it is an exception to the rule. Therefore, add a volatile qualifier to tell the compiler we really want to dereference a zero address. MFC after: 1 week Modified: head/lib/libthr/arch/amd64/include/pthread_md.h head/lib/libthr/arch/i386/include/pthread_md.h Modified: head/lib/libthr/arch/amd64/include/pthread_md.h ============================================================================== --- head/lib/libthr/arch/amd64/include/pthread_md.h Thu Dec 15 17:54:23 2011 (r228535) +++ head/lib/libthr/arch/amd64/include/pthread_md.h Thu Dec 15 19:42:25 2011 (r228536) @@ -71,7 +71,7 @@ struct tcb { u_long __i; \ __asm __volatile("movq %%fs:%1, %0" \ : "=r" (__i) \ - : "m" (*(u_long *)(__tcb_offset(name)))); \ + : "m" (*(volatile u_long *)(__tcb_offset(name)))); \ __result = (__tcb_type(name))__i; \ \ __result; \ Modified: head/lib/libthr/arch/i386/include/pthread_md.h ============================================================================== --- head/lib/libthr/arch/i386/include/pthread_md.h Thu Dec 15 17:54:23 2011 (r228535) +++ head/lib/libthr/arch/i386/include/pthread_md.h Thu Dec 15 19:42:25 2011 (r228536) @@ -70,7 +70,7 @@ struct tcb { u_int __i; \ __asm __volatile("movl %%gs:%1, %0" \ : "=r" (__i) \ - : "m" (*(u_int *)(__tcb_offset(name)))); \ + : "m" (*(volatile u_int *)(__tcb_offset(name)))); \ __result = (__tcb_type(name))__i; \ \ __result; \
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