gcc10 @10.3.0: gcc10 failed to build from source on Big Sur 11.3

[ferdy (Giuseppe `ferdy` Miceli)]

gcc@10.3.0 fails to build from source on Big Sur 11.3

please find /opt/mp/var/macports/logs/_opt_mp_macports-ports_lang_gcc10/gcc10/main.log attached.

terminal input/output

ferdy@wabi:~$ sudo port clean --all --work gcc10
--->  Cleaning gcc10
ferdy@wabi:~$ sudo port -s install libgcc10
<...>
--->  Building gcc10
Error: Failed to build gcc10: command execution failed
Error: See /opt/mp/var/macports/logs/_opt_mp_macports-ports_lang_gcc10/gcc10/main.log for details.

system information

ferdy@wabi:~$ sw_vers
ProductName:	macOS
ProductVersion:	11.3
BuildVersion:	20E232
ferdy@wabi:~$ uname -a
Darwin wabi.ferdy.lan 20.4.0 Darwin Kernel Version 20.4.0: Fri Mar  5 01:14:14 PST 2021; root:xnu-7195.101.1~3/RELEASE_X86_64 x86_64 i386 MacBookPro16,1 Darwin
ferdy@wabi:~$ xcodebuild -version
Xcode 12.5
Build version 12E262
ferdy@wabi:~$ xcode-select -version
xcode-select version 2384.
ferdy@wabi:~$ port version
Version: 2.6.4

[ferdy (Giuseppe `ferdy` Miceli)]

/opt/mp/var/macports/logs/_opt_mp_macports-ports_lang_gcc10/gcc10/main.log

[jmroot (Joshua Root)]

See also #62773. Could well be the same issue and thus a duplicate, but I'm not familiar enough with GCC to say.

[kencu (Ken)]

This is a known issue upstream, and has to do with the way clang now generates objects differently between debug and non-debug cases, leading to a bootstrap compare failure.

"The workaround will be to configure GCC without debug-compare in bootstrap."

[kencu (Ken)]

I don't believe this is a configure.arg we pass to the gcc build, but I think it is a flag that needs to be changed internally in the build of the bootstrap compiler.

We'll have to watch Iain's repos for a fix.

[kencu (Ken)]

Maybe not <​https://gcc.gnu.org/install/build.html>

right now our build uses --with-build-config=bootstrap-debug which is failing.

If we (at least for now, on 11.3+) used --disable-bootstrap instead, I suspect we might get it building again, but without the bootstrapping, which is not ideal.

[cjones051073 (Chris Jones)]

An alternative might be to blacklist (for now) the newer 11.3+ compilers.... I would prefer that to disabling the bootstrapping.

[cjones051073 (Chris Jones)]

p.s. Ken, do you have a link to the upstream issue ?

[kencu (Ken)]

​https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100340

[kencu (Ken)]

this apparently worked --without-build-config

[kencu (Ken)]

blacklisting the compiler won't fix it, as it is due to changes in the assembler implementation.

we could force our older cctools to be used, perhaps, but that is a total yuck option.

edit: forcing our older cctools actually wouldn't work, as they all would just pass to clang to assemble anyway

[cjones051073 (Chris Jones)]

Yeah, I realised blacklist the compiler wouldn't cut it soon after looking into it a bit more....

I think assuming --without-build-config also works for us adding this (for now) as a work around specifically for Xcode 12.5 is the best option.

[kencu (Ken)]

that indeed just disables bootstrapping I believe, but no other good option right now

edit: it actually might still bootstrap, but differently.

[cjones051073 (Chris Jones)]

I also think it might work redirecting the build to use ld from one of the newer LLVM releases instead of cctools {which in turn is just providing a wrapper around the Xcode ld).

[kencu (Ken)]

it's the assembler, according to upstream, so if so, a linker change would not likely be the fix

[ferdy (Giuseppe `ferdy` Miceli)]

(for what is worth) i do confirm that `--without-build-config works and allows building from sources libgcc10 and gcc10.

ferdy@wabi:~$ sudo port -svpfRN install gcc10
<...>
ferdy@wabi:~$ port installed | grep gcc
  gcc10 @10.3.0_20210430 (active)
  gcc_select @0.1_9 (active)
  libgcc @3.0_0 (active)
  libgcc10 @10.3.0_20210430 (active)
ferdy@wabi:~$ 

[Chris Jones <jonesc@…>]

In 3ec93e3430e65f5cb9fb02eab86dfb1803f0a64c/macports-ports (master):

(lib)gcc10: Add configuration work around for macOS 11.3 / Xcode 12.5
Closes: #62775

[kencu (Ken)]

Quick work, everyone!