Building on Mac with --enable-tls

Building on Mac with --enable-tls

[Tom N]

I'm trying to build GCC from source on Mac (darwin) and keep getting this error when --enable-tls is specified:


/var/folders/cq/wx4ff_gd0xncqh9qnbzmt2w40000gp/T//ccS0vBm1.s:9:2: error: unsupported symbol modifier
in relocation
leaq __ZN3GTM12_gtm_thr_tlsE@tlsgd(%rip), %rdi
^
make[5]: *** [alloc_cpp.lo] Error 1


If I either omit --enable-tls or specify --disable-tls the build succeeds, but then I get synchronization problems in my code which uses std::unique_lock<std::mutex>  (namely it seems the synchronization isn't performed).

(Incidentally I've been building GCC for many years on Linux without issue so I'm not new to building GCC.)

I've tried on "fresh" (new system) Mac Yosemite (10.10), Sierra (10.12), and Catalina (10.15) (all having only XCode CLT, none have XCode itself), and GCC 4.9, 8.3, and 8.4.   All fail the same.   I've gleaned as much as I can from reading the Homebrew script that builds the same but still no luck.

I was hoping to find a build log from either GCC's own verification builds or Homebrew in order to compare against my own to find the problem but can't find it.

Here's the configure line from GCC 8.4 on Catalina (some of it may be unnecessary/redundant, it comes from my build toolchain):


cd ./build && CC=gcc CXX=g++ CFLAGS="" CXXFLAGS="" CPPFLAGS="" LDFLAGS="" BOOT_CFLAGS="-iframework /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks -mmacosx-version-min=10.15" CFLAGS_FOR_TARGET="-iframework /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Lib
rary/Frameworks -mmacosx-version-min=10.15" CXXFLAGS_FOR_TARGET="-iframework /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks -mmacosx-version-min=10.15" BOOT_LDFLAGS="-Wl,-headerpad_max_install_names" PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin /Users/me/gcc/gcc-8.4.0/configure --prefix=/Users/me/gcc_build --enable-languages=c,c++ --enable-threads=posix --enable-tls --disable-nls --enable-checking=release --disable-multilib --with-native-system-header-dir="/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include"


Happy to provide anything else that will help.

This has been beating me for a long time, appreciate anything.

Re: Building on Mac with --enable-tls

[Jonathan Wakely]

On Wed, 18 Mar 2020 at 19:15, Tom N <nospam@codesniffer.com> wrote:
>
> I'm trying to build GCC from source on Mac (darwin) and keep getting this error when --enable-tls is specified:
>
>
> /var/folders/cq/wx4ff_gd0xncqh9qnbzmt2w40000gp/T//ccS0vBm1.s:9:2: error: unsupported symbol modifier
> in relocation
> leaq __ZN3GTM12_gtm_thr_tlsE@tlsgd(%rip), %rdi
> ^
> make[5]: *** [alloc_cpp.lo] Error 1
>
>
> If I either omit --enable-tls or specify --disable-tls the build succeeds,

I would expect the default to be correct for the target i.e.
--disable-tls. If enabling it worked correctly, it would be the
default.

> but then I get synchronization problems in my code which uses std::unique_lock<std::mutex>  (namely it seems the synchronization isn't performed).

That makes no sense, neither std::mutex nor std::unique_lock uses TLS.

Re: Building on Mac with --enable-tls

[Iain Sandoe]

Jonathan Wakely <jwakely.gcc@gmail.com> wrote:

> On Wed, 18 Mar 2020 at 19:15, Tom N <nospam@codesniffer.com> wrote:
>> I'm trying to build GCC from source on Mac (darwin) and keep getting  
>> this error when --enable-tls is specified:
>>
>>
>> /var/folders/cq/wx4ff_gd0xncqh9qnbzmt2w40000gp/T//ccS0vBm1.s:9:2: error:  
>> unsupported symbol modifier
>> in relocation
>> leaq __ZN3GTM12_gtm_thr_tlsE@tlsgd(%rip), %rdi
>> ^
>> make[5]: *** [alloc_cpp.lo] Error 1
>>
>>
>> If I either omit --enable-tls or specify --disable-tls the build succeeds,
>
> I would expect the default to be correct for the target i.e.
> --disable-tls. If enabling it worked correctly, it would be the
> default.
>
>> but then I get synchronization problems in my code which uses  
>> std::unique_lock<std::mutex>  (namely it seems the synchronization isn't  
>> performed).
>
> That makes no sense, neither std::mutex nor std::unique_lock uses TLS.

Darwin uses emulatedTLS on all versions (powerpc, i686, x86_64) the correct  
default (to use emulatedTLS) is selected without requiring any additional  
configure options.  Selecting --enable-tls will undoubtedly produce an  
invalid configuration.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52268  is an enhancement PR to  
add native TLS for 10.7+ (but that would still not work on earlier  
versions, of course).

thanks
Iain

Re: Building on Mac with --enable-tls

[Tom N]

> On March 18, 2020 at 7:53 PM Iain Sandoe <idsandoe@googlemail.com> wrote:
> 
> Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> > 
> > I would expect the default to be correct for the target i.e.--disable-tls. If enabling it worked correctly, it would be the default.
> > That makes no sense, neither std::mutex nor std::unique_lock uses TLS.
> 
> Darwin uses emulated TLS on all versions (powerpc, i686, x86_64) the correct default (to use emulatedTLS) is selected without requiring any additional configure options. Selecting --enable-tls will undoubtedly produce an invalid configuration.
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52268 is an enhancement PR to add native TLS for 10.7+ (but that would still not work on earlier versions, of course).

Thank you both for the quick responses!  Knowing that lack of --enable-tls is normal on Mac set me in the right direction.  The synchronization problem was due to an equally bad assumption.  All working as expected now.

Thanks again!

Re: Building on Mac with --enable-tls

[Jonathan Wakely]

On Thu, 19 Mar 2020 at 13:54, Tom N <nospam@codesniffer.com> wrote:
>
> > On March 18, 2020 at 7:53 PM Iain Sandoe <idsandoe@googlemail.com> wrote:
> >
> > Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> > >
> > > I would expect the default to be correct for the target i.e.--disable-tls. If enabling it worked correctly, it would be the default.
> > > That makes no sense, neither std::mutex nor std::unique_lock uses TLS.
> >
> > Darwin uses emulated TLS on all versions (powerpc, i686, x86_64) the correct default (to use emulatedTLS) is selected without requiring any additional configure options. Selecting --enable-tls will undoubtedly produce an invalid configuration.
> >
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52268 is an enhancement PR to add native TLS for 10.7+ (but that would still not work on earlier versions, of course).
>
> Thank you both for the quick responses!  Knowing that lack of --enable-tls is normal on Mac set me in the right direction.  The synchronization problem was due to an equally bad assumption.  All working as expected now.

Accidentally creating a temporary unique_lock that immediately goes
out of scope? :-)

http://kayari.org/cxx/antipatterns.html#locking-mutex

Re: Building on Mac with --enable-tls

[Tom N]

> On March 19, 2020 at 10:07 AM Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> 
> Accidentally creating a temporary unique_lock that immediately goes out of scope? :-)
> http://kayari.org/cxx/antipatterns.html#locking-mutex

Not that bad I think. :)  (The code has been in production on Linux & Windows for years so something like that should've popped up already.)

Actually the bad assumption was that my unit tests were doing sufficient testing of my GetThreadId wrapper.  That wasn't working properly on Mac but not triggering an error either.  The synchronization was not the problem--only the Thread IDs being used as keys into a std::map.

Thanks again!