Re: November 5th is Clang-Day
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On Sun, Nov 04, 2012 at 03:29:42PM +0100, Dimitry Andric wrote:
> On 2012-11-04 14:18, Konstantin Belousov wrote:
> > On Sun, Nov 04, 2012 at 02:42:13PM +0200, David Naylor wrote:
> ...
> >> I tried building (using gcc) wine with your patch and now (at least) w=
inecfg
> >> and regedit work with a clang built lib32. I'll email Gerald (wine's
> >> maintainer) about including your patch in wine.
> >
> > The wine is the wrong place to fix. If system libraries suddenly started
> > requiring 16-byte stack alignment on i386, it is unacceptable breakage
> > of the ABI.
>=20
> So we really must use 4 byte stack alignment on i386 by default? I have
> attached a diff to llvm for this, but I would like to verify that it is
> really correct. Apparently Darwin, Linux and Solaris all use 16 byte
> alignment.
No, this is a misunderstanding.
We must provide libraries that tolerate the 4-byte aligned stack.
Also, to be compatible with broken compilers (both older versions of gcc
and some versions of clang) we must provide the libraries which preserve
the %esp mod 0x10 across the functions entry/leave points.
The crt ensures that the stack is 16-byte aligned on entry to main.
>=20
> The Sys V ABI seems to say only: "The stack is word aligned. Although
> the architecture does not require any alignment of the stack, software
> convention and the operating system requires that the stack be aligned
> on a word boundary".
Right, this is ABI which some binaries follow. There are some other binarie=
s,
generated by arguably broken compilers, which require 16-byte alignment.
The system shall support both.
> Index: contrib/llvm/lib/Target/X86/X86Subtarget.cpp
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- contrib/llvm/lib/Target/X86/X86Subtarget.cpp (revision 242480)
> +++ contrib/llvm/lib/Target/X86/X86Subtarget.cpp (working copy)
> @@ -416,12 +416,12 @@ X86Subtarget::X86Subtarget(const std::string &TT,
> assert((!In64BitMode || HasX86_64) &&
> "64-bit code requested on a subtarget that doesn't support it!"=
);
> =20
> - // Stack alignment is 16 bytes on Darwin, FreeBSD, Linux and Solaris (=
both
> - // 32 and 64 bit) and for all 64-bit targets.
> + // Stack alignment is 16 bytes on Darwin, Linux and Solaris (both 32 a=
nd 64
> + // bit) and for all 64-bit targets.
> if (StackAlignOverride)
> - stackAlignment =3D StackAlignOverride;
> - else if (isTargetDarwin() || isTargetFreeBSD() || isTargetLinux() ||
> - isTargetSolaris() || In64BitMode)
> + stackAlignment =3D StackAlignOverride;
> + else if (isTargetDarwin() || isTargetLinux() || isTargetSolaris() ||
> + In64BitMode)
> stackAlignment =3D 16;
> }
> =20
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