External LLVM toolchain not consistently locating c++ when compiling ports

[Mark Millard]

On 2017-Oct-29, at 12:10 AM, Sid <sid at bsdmail.com> wrote:

> This is not on Qemu, and I'm not cross-building. This is on an amd64 on 11.1-RELEASE-p2. Base was built without clang or gcc, and clang40 was installed from ports.
> 
> The base and kernel compile using lang/llvm40 with XCC, XCXX, and XCPP set. I'm a little confused, as how earlier, it seemed that ports that didn't need c++ were building without CC, CXX, and CPP options set.  If I made a mistake here, I apologize for this. It seems CC, CXX, and CPP are made for ports. Then the problem is with Rust locating c++ that is in /usr/local/bin/ and not contained within FreeBSD 11.1's base, in /usr/bin/.
> 
> Nearly all programs requiring c++, needed for my desktop (xorg, rxvt-unicode, leafpad, sox) compiled when all 6 variables were set (CC,CPP, etc). Only Rust, and programs depending on it failed. Now I think the problem is, that Rust and programs depending on it look in absolute locations for c++.

I'm afraid there is a clang++40 to find but no c++
to be found anywhere in your context based on what
you have described.

I have llvm50 installed instead of llvm40, so, that is what
I'll use as an example for amd64 (head -r324743 ). . .

# pkg info llvm50
llvm50-5.0.0_1
Name           : llvm50
Version        : 5.0.0_1
Installed on   : Sun Sep 24 00:26:47 2017 PDT
Origin         : devel/llvm50
Architecture   : FreeBSD:12:amd64
Prefix         : /usr/local
Categories     : devel lang
Licenses       : LLVM
Maintainer     : brooks at FreeBSD.org
WWW            : http://llvm.org/
Comment        : LLVM and Clang
Options        :
	CLANG          : on
	COMPILER_RT    : on
	DOCS           : on
	EXTRAS         : on
	GOLD           : on
	LIT            : on
	LLD            : on
	LLDB           : on
	OPENMP         : on
. . .

But no command c++ is under /usr/local/ ,
there is just a directory of that name
(from lang/gcc7 in my context):

# find /usr/local -name c++ -print | more
/usr/local/lib/gcc7/include/c++

Clang++50 is under its own name:

# which clang++50
/usr/local/bin/clang++50

So without system clang (or system gcc 4.2.1) and only
with llvm40 I expect that there is no c++ command at all.
The issue would not be an overly-specific path: no path
would work.

Rust needs to not be looking for a c++ command at all.
It needs to be using ${CXX} and the like that would
need to involve clang++50 .

But you can make a local workaround by creating your
own c++ command someplace in the paths being checked,
either linking to or copying clang++40 to produce the
c++ . c++ might not be the only file needing such
a technique.

Prior material follows, nothing new so likely skip. . .

> Sent: Sunday, October 29, 2017 at 12:11 AM
> From: "Mark Millard" <markmi at dsl-only.net>
> To: Sid <sid at bsdmail.com>
> Cc: freebsd-toolchain at freebsd.org
> Subject: Re: External LLVM toolchain not consistently locating c++ when compiling ports
> 
> 
> On 2017-Oct-28, at 9:40 PM, Sid <sid at bsdmail.com> wrote:
> 
>> In /etc/make.conf, when I use,
>> XCC=	/usr/local/bin/clang40
>> XCXX=	/usr/local/bin/clang++40
>> XCPP=	/usr/local/bin/clang-cpp40
>> for ports that require c++ without clang in the base system, I get the error code 
>>  make: "/usr/ports/Mk/Uses/compiler.mk" line 112:warning: "c++ -### /dev/null 2>&1" returned non-zero status
> 
> Quoting https://wiki.freebsd.org/ExternalToolchain:
> 
> XCC
> 
> The XCC approach works with top level build targets (buildworld, buildkernel, etc) and overrides common make variables such as CC, CXX, and AS during the cross building portions of the build with values specified by the XCC, XCPP, XAS, etc variables. This method touches few files and is relatively easy to understand, but has drawbacks including the inability to build individual programs easily. 
> 
> END QUOTE.
> 
> Does ports support "cross building" that would be expected to use
> XCC, XCXX, XCPP, and the like?
> 
> To my knowledge there is no cross build environment for ports
> that can avoid qemu (or an equivalent): cross builds of parts
> are based on qemu, which use CC, CXX, CPP and the like as far
> as I know.
> 
>> Base and the kernel builds well with this setting. Compiles that don't need c++ also work with this setting.
> 
> Unlike for ports builds. (That is my understanding.)
> 
>> I've compensated by adding
>> CC=	/usr/local/bin/clang40
>> CXX=	/usr/local/bin/clang++40
>> CPP=	/usr/local/bin/clang-cpp40
>> to the above. While this works for many ports requiring c++, it doesn't work for Rust, and programs that depend on it (Firefox, Thunderbird).
> 
> This is what I'd expect for "self hosted" (target=build)
> types of contexts and for being in a qemu context that looks
> like the target.
> 
> I'm not aware of another form of cross build for
> FreeBSD ports. (I'd like to be able to do powerpc64
> and powerpc without a system qemu. User qemu does
> not work for targeting powerpc64 or for powerpc.)
> 
>> It seems that XCXX is supposed to replace CXX fully, considering that XCC replaces CC, and XCPP replaces CPP when compiling other ports.
> 
> Can you provide evidence of this? Does the evidence
> involve cross building where the X prefix is involved?
> 
>> The error message for compiling rust with all of the above (XCC, XCXX, XCPP, CC, CXX, CPP) set is
>>  couldn't find required command: "c++"
> 
> Does the environment not have a c++ command in a place
> listed in path? Otherwise it should be found.
> 
>> This error happens whether the port option for lang/rust is set to compile with llvm40 or the bundled version.
>> This is affected by /usr/ports/Mk/Uses/compiler.mk and I think this problem affects ports compiled with c++ in the base system as well.


===
Mark Millard
markmi at dsl-only.net