On Sat, Oct 10, 2015 at 11:37:26AM +0000, Ed Maste wrote: > On 10 October 2015 at 06:08, Konstantin Belousov <kostik...@gmail.com> wrote: > > On Fri, Oct 09, 2015 at 06:21:45PM +0000, Dimitry Andric wrote: > >> Author: dim > >> Date: Fri Oct 9 18:21:45 2015 > >> New Revision: 289072 > >> URL: https://svnweb.freebsd.org/changeset/base/289072 > >> > >> Log: > >> Temporarily revert upstream llvm trunk r240144 (by Michael Zolotukhin): > > > > This might be indeed a clang bug, but probably not in the revision which > > you reverted. Or it might be a libc++ bug. > > Yes, the bug is almost certainly not r240144; reverting it is a > short-term workaround until the underlying issue is fixed. > > > The story, from what I understand from the discussion at some other > > place, is that the fault occurs on access to the common unaligned > > symbol. Apparently, ELF does allow to specify alignment of the common > > symbols, and static linker, when finally allocating .bss space for the > > object, must obey the requirement. The symbol value for the common > > symbol must be interpreted as the desired alignment. > > > > Could you look up the symbol reference in the .o files (again) and see > > which alignment is requested ? I think that it is probably clang which > > should set it to be at least 16 bytes to generate ABI-compliant code. > > The declaration is extern ostream cout; which correctly has 8 byte alignment. The alignment of the declaration does not matter, most likely. I am not sure what you mean by saying that 8 byte alignment is desirable, while compiler generates accesses (movdqa) which assume 16-byte alignment.
> > In the implementation (contrib/libc++/src/iostream.cpp) it is defined > as a char array which is where the 16-byte ABI alignment would arise, > but explicitly specifies 8-byte alignment: > _ALIGNAS_TYPE (ostream) _LIBCPP_FUNC_VIS char cout[sizeof(ostream)]; > > Compiling with -emit-llvm --save-temps shows the desired 8-byte > alignment for cout in the LLVM IR but 16-byte in the assembly file. Could somebody show the readelf -s iostream.So and readelf -s libc++.so.X output lines for the symbol, please ? _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
