On Wed, Sep 13, 2017 at 08:44:24AM +0000, Miod Vallat wrote:
>
> > Forcing uextraloc into .data via
> > int uextraloc __attribute__ ((section(".data"))) = 0;
> > avoids the crashes.
>
> Regardless of this bug, the in-tree gcc was modified to default to put
> explicitly zero initialized data in .data rather than .bss, i.e. default
> to -fno-zero-initialized-in-bss.
>
> It might be wise to make the default configuration of clang follow this
> behaviour as well.
>
Yes, that seems reasonable.
Index: gnu/llvm/tools/clang/lib/Driver/Tools.cpp
===================================================================
RCS file: /cvs/src/gnu/llvm/tools/clang/lib/Driver/Tools.cpp,v
retrieving revision 1.14
diff -u -p -r1.14 Tools.cpp
--- gnu/llvm/tools/clang/lib/Driver/Tools.cpp 28 Jul 2017 15:31:54 -0000
1.14
+++ gnu/llvm/tools/clang/lib/Driver/Tools.cpp 13 Sep 2017 09:51:50 -0000
@@ -4463,8 +4463,13 @@ void Clang::ConstructJob(Compilation &C,
if (shouldUseFramePointer(Args, getToolChain().getTriple()))
CmdArgs.push_back("-mdisable-fp-elim");
+
+ bool ZeroInitializedInBSSDefault = true;
+ if (getToolChain().getTriple().isOSOpenBSD())
+ ZeroInitializedInBSSDefault = false;
if (!Args.hasFlag(options::OPT_fzero_initialized_in_bss,
- options::OPT_fno_zero_initialized_in_bss))
+ options::OPT_fno_zero_initialized_in_bss,
+ ZeroInitializedInBSSDefault))
CmdArgs.push_back("-mno-zero-initialized-in-bss");
bool OFastEnabled = isOptimizationLevelFast(Args);
Index: share/man/man1/clang-local.1
===================================================================
RCS file: /cvs/src/share/man/man1/clang-local.1,v
retrieving revision 1.9
diff -u -p -r1.9 clang-local.1
--- share/man/man1/clang-local.1 29 Jul 2017 21:01:13 -0000 1.9
+++ share/man/man1/clang-local.1 13 Sep 2017 09:57:14 -0000
@@ -95,6 +95,14 @@ and
.Xr free 3
builtins are disabled to prevent undesriable optimizations of calls to
these functions.
+.It
+.Nm clang
+will not move variables initialized with the value zero from the data section
+to the bss section.
+The default behaviour of
+.Nm clang
+on other systems is to perform this action, which can be restored with
+.Fl fzero-initialized-in-bss .
.El
.Sh SEE ALSO
.Xr clang 1
