<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Nov 16, 2018, at 12:21, JF Bastien <<a href="mailto:jfbastien@apple.com" class="">jfbastien@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div class=""><br class=""><blockquote type="cite" class=""><div class="">On Nov 16, 2018, at 5:06 AM, Louis Dionne <<a href="mailto:ldionne@apple.com" class="">ldionne@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><br class="Apple-interchange-newline"><br class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;"><div class="">On Nov 16, 2018, at 00:18, JF Bastien via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><br class="Apple-interchange-newline"><br class=""><blockquote type="cite" class=""><div class="">On Nov 15, 2018, at 5:41 PM, Kristina Brooks via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Well that was in my original suggestion, but I don't know who is in charge of IA64 mangling, I<br class="">don't think Clang developers can push a change like this forward without some RFC to whatever<br class="">committee maintains the IA64 ABI or am I wrong? I suppose libc++ ABI could be considered separate<br class="">enough in which case we just need to come up with a compatible scheme for "short" manglings that<br class="">is also guaranteed not to clash with the standard IA64 ABI.<br class=""><br class="">Since you and Eric are mostly in charge of libcxxabi, could you propose a draft for a compatible<br class="">short mangling that would allow doing this as a breaking change (for unstable ABI versions, even<br class="">2+ since it's not stable yet unless Fuchsia has settled on it)? That way it's possible to add that<br class="">into the Clang mangler. I'm still not sure if this requires a blessing from whoever is in charge<br class="">of IA64 ABI, I think that would be a good idea to mention the draft to them at least.<br class=""></div></div></blockquote><div class=""><br class=""></div><div class="">According to: <a href="https://itanium-cxx-abi.github.io/cxx-abi/" class="">https://itanium-cxx-abi.github.io/cxx-abi/</a></div><div class=""><br class=""></div><div class="">The primary discussion forum for the ABI is the <a href="http://github.com/itanium-cxx-abi/cxx-abi/" class="">GitHub repository</a>. Please open a new issue for any new topic you want to discuss. Previously, the ABI was discussed on a mailing list, cxx-abi-dev, whose <a href="http://sourcerytools.com/pipermail/cxx-abi-dev/" class="">archives</a> are still accessible.</div><div class=""><br class=""></div><div class="">CC’ing John since he’ll know more about this, seeing as how he’s the most active contributor to the repository :-)</div><div class=""><br class=""></div><div class="">This issue from Richard seems like a good starting point: <a href="https://github.com/itanium-cxx-abi/cxx-abi/issues/42" class="">https://github.com/itanium-cxx-abi/cxx-abi/issues/42</a></div><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div class="">Thanks.<br class=""><br class="">On 16/11/2018 01:26, Louis Dionne wrote:<br class=""><blockquote type="cite" class=""><br class=""><br class=""><blockquote type="cite" class="">On Nov 15, 2018, at 20:06, JF Bastien via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:<br class=""><br class=""><br class=""><br class=""><blockquote type="cite" class="">On Nov 15, 2018, at 3:59 PM, Kristina Brooks via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a>> wrote:<br class=""><br class="">Yes exactly, seems like an obvious win on a mono-ABI system, if preserving debug data<br class="">this saves a lot, not to mention symbol table strings. Also, I'm purely speculating here<br class="">but this would also speed up compilation and linking time by an insignificant margin, but<br class="">nevertheless, it's an improvement.<br class=""><br class="">If the ABI ever needs to change, on those kinds of systems, it's easy enough with an OS<br class="">update.<br class=""></blockquote><br class="">Or, we could update the Itanium ABI so that the current mangling still works and is compatible with a new mangling which is shorter for libc++ (yet remains purposefully incompatible with libstdc++’s mangling) 🙂<br class=""><br class=""></blockquote><br class="">Is it necessary/desirable to distinguish between implementations of the standard library at the Itanium ABI level? Wouldn't it be possible to define a compressed scheme for `std::__N` in full generality, and handle the ability to differentiate between implementations differently?<br class=""></blockquote></div></div></blockquote><div class=""><br class=""></div><div class="">What I had in mind was distinguishing `std::__N` as you say, and by construction that would distinguish between implementations because libc++ and libstdc++ use different namespaces.</div></div></div></blockquote><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;" class=""><br class=""></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;" class="">But that would also prevent libstdc++ from ever using that mangling scheme (not that I care about libstdc++, but you know).</div></div></blockquote><div class=""><br class=""></div><div class="">Not really, they can share the namespace if we don’t collide. They get the odd numbers we get the even ones? As long as we don’t cause ABI mismatches it’s fine.</div></div></div></div></blockquote><div><br class=""></div><div>Actually, I think the Itanium ABI provides a way to add vendor-specific tags to mangling:</div><div><br class=""></div><div><span style="font-family: -webkit-standard; font-size: medium;" class="">A </span><code style="font-weight: bold;" class=""><<a href="http://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangle.mangled-name" class="">mangled-name</a>></code><span style="font-family: -webkit-standard; font-size: medium;" class=""> containing a period represents a vendor-specific version or portion of the entity named by the </span><code style="font-weight: bold;" class=""><<a href="http://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangle.encoding" class="">encoding</a>></code><span style="font-family: -webkit-standard; font-size: medium;" class=""> prior to the first period. There is no restriction on the characters that may be used in the suffix following the period.</span></div><div><span style="font-family: -webkit-standard; font-size: medium;" class=""><br class=""></span></div><div>So if libstdc++ wanted to use inline namespaces for versioning, they could do it with a bit of tooling support IIUC.</div><div><br class=""></div><div>Re-reading this, I'm now wondering why we're not piggy-backing on this mechanism to encode the version of libc++? It does seem like this mechanism was made explicitly for that use case.</div><div><br class=""></div><div>Louis</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;" class="">Louis</div><br class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none;"><div class=""><div class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class="">Louis<br class=""><br class=""><blockquote type="cite" class=""><br class=""><blockquote type="cite" class="">Thanks.<br class=""><br class="">On 14/11/2018 17:06, Eric Fiselier wrote:<br class=""><blockquote type="cite" class=""><br class=""><br class="">On Wed, Nov 14, 2018 at 12:04 PM Eric Fiselier <<a href="mailto:eric@efcs.ca" class="">eric@efcs.ca</a><span class="Apple-converted-space"> </span><<a href="mailto:eric@efcs.ca" class="">mailto:eric@efcs.ca</a>>> wrote:<br class=""><br class=""> The itanium specification provides special compressed mangled names for std::string when it's not in an inline<br class=""> namespace [1]<br class=""><br class=""> Specifically, `Ss` vs `St3__112basic_string`<br class=""><br class=""><br class="">Correction... `Ss` vs `NSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEE`<br class=""><br class=""><br class=""><br class=""> [1]<span class="Apple-converted-space"> </span><a href="https://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling-compression" class="">https://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling-compression</a><br class=""><br class=""> On Wed, Nov 14, 2018 at 10:03 AM Marshall Clow via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a><br class=""> <<a href="mailto:libcxx-dev@lists.llvm.org" class="">mailto:libcxx-dev@lists.llvm.org</a>>> wrote:<br class=""><br class=""> On Sun, Nov 11, 2018 at 9:49 PM Kristina Brooks via libcxx-dev <<a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a><br class=""> <<a href="mailto:libcxx-dev@lists.llvm.org" class="">mailto:libcxx-dev@lists.llvm.org</a>>> wrote:<br class=""><br class=""> Hi,<br class=""><br class=""> I was wondering, would it be possible to add an option to disable inline namespacing completely (as a CMake<br class=""> configuration flag) in libc++ for the sake of being able to use shorthand mangling and without having to<br class=""> resort to<br class=""> handling it on IA64 mangler level. This has many use cases for example distributions of anything that<br class=""> includes libc++ as<br class=""> one and only libc++ and does not allow non-vendor software to be installed. On an embedded system, assuming<br class=""> debug info<br class=""> is generated, and given how common some of the debug data takes a very significant amount of space given the<br class=""> complex<br class=""> definition of something like `std::__2::basic_string<...>` versus the short form (`std::string` having a<br class=""> shorthand<br class=""> mangling is a godsend since it's 95% shorter, not an accurate figure but basically definitely above 90%).<br class=""><br class=""><br class=""> I'm confused here.<br class=""> Why are you comparing `std::string` to `std::__2::basic_string<......" ?<br class=""><br class=""> `std::__2::string` is quite short.<<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev</a>><br class=""><br class=""> -- Marshall<br class=""><br class=""> _______________________________________________<br class=""> libcxx-dev mailing list<br class=""> <a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a><span class="Apple-converted-space"> </span><<a href="mailto:libcxx-dev@lists.llvm.org" class="">mailto:libcxx-dev@lists.llvm.org</a>><br class=""> <a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev</a><br class=""><br class=""></blockquote>_______________________________________________<br class="">libcxx-dev mailing list<br class=""><a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a><br class=""><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev</a><br class=""></blockquote><br class="">_______________________________________________<br class="">libcxx-dev mailing list<br class=""><a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a><br class=""><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev</a><br class=""></blockquote><br class=""></blockquote>_______________________________________________<br class="">libcxx-dev mailing list<br class=""><a href="mailto:libcxx-dev@lists.llvm.org" class="">libcxx-dev@lists.llvm.org</a><br class=""><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev</a><br class=""></div></div></blockquote></div><br class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><span class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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; float: none; display: inline !important;">_______________________________________________</span><br class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><span class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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; float: none; display: inline !important;">libcxx-dev mailing list</span><br class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><a href="mailto:libcxx-dev@lists.llvm.org" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">libcxx-dev@lists.llvm.org</a><br class="" style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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;"><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">http://lists.llvm.org/cgi-bin/mailman/listinfo/libcxx-dev</a></div></blockquote></div></blockquote></div><br class=""></div></div></blockquote></div><br class=""></body></html>