From b34d83a709b17733984f7ea74c6451892a5db9a8 Mon Sep 17 00:00:00 2001 From: Dimitry Andric Date: Thu, 15 Dec 2011 19:42:25 +0000 Subject: [PATCH] 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 --- lib/libthr/arch/amd64/include/pthread_md.h | 2 +- lib/libthr/arch/i386/include/pthread_md.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/libthr/arch/amd64/include/pthread_md.h b/lib/libthr/arch/amd64/include/pthread_md.h index 9f6d3a137dc8..0ebea2e3bd24 100644 --- a/lib/libthr/arch/amd64/include/pthread_md.h +++ b/lib/libthr/arch/amd64/include/pthread_md.h @@ -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; \ diff --git a/lib/libthr/arch/i386/include/pthread_md.h b/lib/libthr/arch/i386/include/pthread_md.h index 5c00cf694d31..c160aa4fb4ad 100644 --- a/lib/libthr/arch/i386/include/pthread_md.h +++ b/lib/libthr/arch/i386/include/pthread_md.h @@ -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; \