Date: Mon, 29 Jul 2024 22:14:55 -0700 From: Mark Millard <marklmi@yahoo.com> To: Dimitry Andric <dim@FreeBSD.org> Cc: Charlie Li <vishwin@freebsd.org>, freebsd-arch <freebsd-arch@freebsd.org>, FreeBSD Toolchain <freebsd-toolchain@freebsd.org> Subject: Re: FreeBSD libc++ , ports, and import std or import std.compat : what if potential ports start using them over time? Message-ID: <98D4961E-2BEF-465E-8ACE-99587A089951@yahoo.com> In-Reply-To: <03578B4A-BA6A-4F9D-BCE0-9C01A84623C5@FreeBSD.org> References: <87497F2F-8C4F-48C8-8737-979070B41C78.ref@yahoo.com> <87497F2F-8C4F-48C8-8737-979070B41C78@yahoo.com> <5ef8f532-e411-449e-9d0e-798ad9da3c3f@freebsd.org> <22A8133D-B6E6-4818-932A-5D6B03882AC4@yahoo.com> <03578B4A-BA6A-4F9D-BCE0-9C01A84623C5@FreeBSD.org>
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On Jul 29, 2024, at 09:18, Dimitry Andric <dim@FreeBSD.org> wrote:
> On 29 Jul 2024, at 18:01, Mark Millard <marklmi@yahoo.com> wrote:
>>=20
>> On Jul 29, 2024, at 07:54, Charlie Li <vishwin@freebsd.org> wrote:
>>> ...
>=20
>>> While you're talking about std and std.compat, I have a related =
issue whilst working on the www/webkit2-gtk update. They have code that =
relies on a std::pair implementation/ABI that does not work with our =
base system libc++. This is because our base system uses LLVM libc++ ABI =
version 1, but the needed implementation is in ABI version 2, which they =
have still (even in trunk!) not declared stable.
>>=20
>> FreeBSD updating its C++ ABI would be a rather major change,
>> or so I would expect. Likely avoided as long as possible?
>>=20
>> I wonder what property of std::pair's implementation is at
>> issue for the ABI version distinction(s).
>=20
> It's a bit of a historical wart that is hard to get rid of. In FreeBSD =
we were "too early" and changed our standard C++ library to libc++ =
before this std::pair trivial copy constructor issue was hashed out in =
the standards committees.
Looking, I eventually found ( __config ):
# elif _LIBCPP_ABI_VERSION =3D=3D 1
. . .
# if defined(__FreeBSD__)
# define _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
# endif
and ( __utility/pair.h ):
template <class _T1, class _T2>
struct _LIBCPP_TEMPLATE_VIS pair
#if defined(_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR)
: private __non_trivially_copyable_base<_T1, _T2>
#endif
{
. . .
So this is not a 1 vs. 2 issue: it is a FreeBSD-specific odd definition =
of 1 that
does not apply to other contexts with _LIBCPP_ABI_VERSION =3D=3D 1 . I'd =
not
noticed that in the prior references that I'd run into. (It fits with =
your wording
below, sort of "early 1 vs. late 1" to invent terminology.)
> After it was settled in those committees, libc++ changed its =
implementation to match, but this actually breaks the ABI!
Sort of "FreeBSD early libc++ ABI 1" vs. "normal late libc++ ABI 1" =
ABIs.
> For anybody who switched to libc++ after that time, there was no =
problem using the new ABI, but in FreeBSD we have been stuck with the =
older interpretation ever since.
>=20
> Changing the ABI involves bumping libc++.so to .2, and putting =
libc++.so.1 into a 'compat' package for the sake of old binaries. I had =
originally wanted to do this for FreeBSD 14 but never got to it, and for =
some reason upstream is also stalled for years now in bumping their own =
official ABI version to 2.
If FreeBSD wants an officially stable libc++ without the forced =
__non_trivially_copyable_base<_T1, _T2> then it could:
) have libc++.so use .2 for libc++ _LIBCPP_ABI_VERSION =3D=3D 1 without =
_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR defined
) have the _LIBCPP_ABI_VERSION =3D=3D 1 with =
_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR defined case for =
libc++.so.1 put into that 'compat' package for the sake of old binaries
There is no reason to need to deal with _LIBCPP_ABI_VERSION =3D=3D 2 at =
all for the issue at hand.
(Yes, this would mean going forward that for N>=3D 1, libc++.so.(N+1) =
would be for _LIBCPP_ABI_VERSION =3D=3D N without the FreeBSD oddity.)
> It would be preferable if upstream libc++ bumps its 'stable' ABI to 2 =
and starts working on 3 as the then-experimental one, then all =
downstream consumers can upgrade, leaving all compat crutches behind.
>=20
How important is having a numerical match for =
libc++.so.(_LIBCPP_ABI_VERSION) instead of the +/- 1 shifting between =
the .so and the _LIBCPP_ABI_VERSION ?
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; =
charset=3Dus-ascii"></head><body style=3D"overflow-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;">On Jul 29, =
2024, at 09:18, Dimitry Andric <dim@FreeBSD.org> =
wrote:<br><div><br class=3D"Apple-interchange-newline"><div><blockquote =
type=3D"cite">On 29 Jul 2024, at 18:01, Mark Millard =
<marklmi@yahoo.com> wrote:<br><blockquote type=3D"cite"><br>On Jul =
29, 2024, at 07:54, Charlie Li <vishwin@freebsd.org> =
wrote:<br><blockquote =
type=3D"cite">...<br></blockquote></blockquote><br><blockquote =
type=3D"cite"><blockquote type=3D"cite">While you're talking about std =
and std.compat, I have a related issue whilst working on the =
www/webkit2-gtk update. They have code that relies on a std::pair =
implementation/ABI that does not work with our base system libc++. This =
is because our base system uses LLVM libc++ ABI version 1, but the =
needed implementation is in ABI version 2, which they have still (even =
in trunk!) not declared stable.<br></blockquote><br>FreeBSD updating its =
C++ ABI would be a rather major change,<br>or so I would expect. Likely =
avoided as long as possible?<br><br>I wonder what property of =
std::pair's implementation is at<br>issue for the ABI version =
distinction(s).<br></blockquote><br>It's a bit of a historical wart that =
is hard to get rid of. In FreeBSD we were "too early" and changed our =
standard C++ library to libc++ before this std::pair trivial copy =
constructor issue was hashed out in the standards =
committees.</blockquote><div><br></div><div>Looking, I eventually found =
( <span style=3D"color: rgb(16, 16, 16); font-family: Monaco; =
font-size: 10px; background-color: rgb(255, 255, =
255);">__config</span> ):</div><div><br></div><div><p =
style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures"># elif =
_LIBCPP_ABI_VERSION =3D=3D 1</span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);">. . .</p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures"># if =
defined(__FreeBSD__)</span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures"># =
define =
_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR</span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures"># =
endif</span></p></div><div><br></div><div>and ( <span style=3D"color:=
rgb(16, 16, 16); font-family: Monaco; font-size: 10px; =
background-color: rgb(255, 255, =
255);">__utility/pair.h</span> ):</div><div><br></div><div><p =
style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures">template <class =
_T1, class _T2></span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures">struct =
_LIBCPP_TEMPLATE_VIS pair</span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures">#if =
defined(_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR)</span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures"> : =
private __non_trivially_copyable_base<_T1, _T2></span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: no-common-ligatures">#endif</span></p>
<p style=3D"margin: 0px; font-stretch: normal; font-size: 10px; =
line-height: normal; font-family: Monaco; font-size-adjust: none; =
font-kerning: auto; font-variant-alternates: normal; =
font-variant-ligatures: normal; font-variant-numeric: normal; =
font-variant-east-asian: normal; font-variant-position: normal; =
font-feature-settings: normal; font-optical-sizing: auto; =
font-variation-settings: normal; color: rgb(16, 16, 16); =
background-color: rgb(255, 255, 255);"><span =
style=3D"font-variant-ligatures: =
no-common-ligatures">{</span></p></div><div><span =
style=3D"font-variant-ligatures: no-common-ligatures">. . =
.</span></div><div><span style=3D"font-variant-ligatures: =
no-common-ligatures"><br></span></div><div><span =
style=3D"font-variant-ligatures: no-common-ligatures">So this is not a 1 =
vs. 2 issue: it is a FreeBSD-specific odd definition of 1 =
that</span></div><div><span style=3D"font-variant-ligatures: =
no-common-ligatures">does not apply to other contexts =
with </span><span style=3D"caret-color: rgb(16, 16, 16); color: =
rgb(16, 16, 16); font-family: Monaco; font-size: 10px; background-color: =
rgb(255, 255, 255);">_LIBCPP_ABI_VERSION =3D=3D 1</span> . I'd =
not</div><div>noticed that in the prior references that I'd run into. =
(It fits with your wording</div><div>below, sort of "early 1 vs. late 1" =
to invent terminology.)</div><br><blockquote type=3D"cite">After it was =
settled in those committees, libc++ changed its implementation to match, =
but this actually breaks the ABI!</blockquote><div><br></div><div>Sort =
of "FreeBSD early libc++ ABI 1" vs. "normal late libc++ ABI 1" =
ABIs.</div><br><blockquote type=3D"cite">For anybody who switched to =
libc++ after that time, there was no problem using the new ABI, but in =
FreeBSD we have been stuck with the older interpretation ever =
since.<br><br>Changing the ABI involves bumping libc++.so to .2, and =
putting libc++.so.1 into a 'compat' package for the sake of old =
binaries. I had originally wanted to do this for FreeBSD 14 but never =
got to it, and for some reason upstream is also stalled for years now in =
bumping their own official ABI version to =
2.<br></blockquote><div><br></div><div>If FreeBSD wants an officially =
stable libc++ without the forced <span style=3D"caret-color: =
rgb(16, 16, 16); color: rgb(16, 16, 16); font-family: Monaco; font-size: =
10px; background-color: rgb(255, 255, =
255);">__non_trivially_copyable_base<_T1, _T2></span> then it =
could:</div><div><br></div><div>) have libc++.so use .2 for =
libc++ <span style=3D"caret-color: rgb(16, 16, 16); color: rgb(16, =
16, 16); font-family: Monaco; font-size: 10px; background-color: =
rgb(255, 255, 255);">_LIBCPP_ABI_VERSION =3D=3D =
1</span> without <span style=3D"caret-color: rgb(16, 16, 16); =
color: rgb(16, 16, 16); font-family: Monaco; font-size: 10px; =
background-color: rgb(255, 255, =
255);">_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR</span> d=
efined</div><div><br></div><div>) have the <span =
style=3D"caret-color: rgb(16, 16, 16); color: rgb(16, 16, 16); =
font-family: Monaco; font-size: 10px; background-color: rgb(255, 255, =
255);">_LIBCPP_ABI_VERSION =3D=3D 1</span> with <span =
style=3D"caret-color: rgb(16, 16, 16); color: rgb(16, 16, 16); =
font-family: Monaco; font-size: 10px; background-color: rgb(255, 255, =
255);">_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR</span> d=
efined case for libc++.so.1 put into that 'compat' package for the sake =
of old binaries</div><div><br></div><div>There is no reason to need to =
deal with <span style=3D"caret-color: rgb(16, 16, 16); color: =
rgb(16, 16, 16); font-family: Monaco; font-size: 10px; background-color: =
rgb(255, 255, 255);">_LIBCPP_ABI_VERSION =3D=3D</span><span =
style=3D"caret-color: rgb(16, 16, 16); color: rgb(16, 16, 16); =
font-family: Monaco; font-size: 10px; background-color: rgb(255, 255, =
255);"> 2</span> at all for the issue at =
hand.</div><div><br></div><div>(Yes, this would mean going forward that =
for N>=3D 1, libc++.so.(N+1) would be for <span =
style=3D"caret-color: rgb(16, 16, 16); color: rgb(16, 16, 16); =
font-family: Monaco; font-size: 10px; background-color: rgb(255, 255, =
255);">_LIBCPP_ABI_VERSION =3D=3D</span><span style=3D"caret-color: =
rgb(16, 16, 16); color: rgb(16, 16, 16); font-family: Monaco; font-size: =
10px; background-color: rgb(255, 255, 255);"> N</span> without =
the FreeBSD oddity.)</div><div><br></div><blockquote type=3D"cite">It =
would be preferable if upstream libc++ bumps its 'stable' ABI to 2 and =
starts working on 3 as the then-experimental one, then all downstream =
consumers can upgrade, leaving all compat crutches =
behind.<br><br></blockquote><div><br></div>How important is having a =
numerical match for <span style=3D"caret-color: rgb(0, 0, 0); =
color: rgb(0, 0, 0);">libc++.so.(</span><span style=3D"caret-color: =
rgb(16, 16, 16); color: rgb(16, 16, 16); font-family: Monaco; font-size: =
10px; background-color: rgb(255, 255, =
255);">_LIBCPP_ABI_VERSION</span><span style=3D"caret-color: rgb(0, 0, =
0); color: rgb(0, 0, 0);">)</span> instead of the +/- 1 shifting =
between the .so and the <span style=3D"caret-color: rgb(16, 16, =
16); color: rgb(16, 16, 16); font-family: Monaco; font-size: 10px; =
background-color: rgb(255, 255, =
255);">_LIBCPP_ABI_VERSION</span> ?</div><div><br></div></div><br><di=
v>
<div dir=3D"auto" style=3D"caret-color: rgb(0, 0, 0); color: rgb(0, 0, =
0); letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; text-decoration: none; word-wrap: =
break-word; -webkit-nbsp-mode: space; line-break: =
after-white-space;"><div dir=3D"auto" style=3D"caret-color: rgb(0, 0, =
0); color: rgb(0, 0, 0); letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: =
none; word-wrap: break-word; -webkit-nbsp-mode: space; line-break: =
after-white-space;"><div dir=3D"auto" style=3D"color: rgb(0, 0, 0); =
letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; word-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;"><div =
style=3D"word-wrap: break-word; -webkit-nbsp-mode: space; line-break: =
after-white-space;"><div style=3D"color: rgb(0, 0, 0); =
font-variant-caps: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style=3D"orphans:=
2; widows: 2; margin: 0px; line-height: normal;"><font face=3D"Courier =
New">=3D=3D=3D</font></div><div style=3D"orphans: 2; widows: 2; margin: =
0px; line-height: normal;"><font face=3D"Courier New">Mark =
Millard</font></div><div style=3D"orphans: 2; widows: 2; margin: 0px; =
line-height: normal;"><font face=3D"Courier New"><span style=3D"font-size:=
12px;">marklmi at =
yahoo.com<br></span></font></div></div></div></div></div></div>
</div>
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