llvm dev - Mar 2017 - Use of host/target compiler when building compiler-rt

On Wed, Mar 8, 2017 at 2:55 PM Chris Bieneman <beanz at apple.com> wrote:
> David,
>
> This is an area that has had a lot of development over the last two years.
>
> There are two supported ways in the LLVM build system to build compiler-rt
> with the just-built compiler.
>
> 1) The legacy way is for if compiler-rt is under LLVM/projects. You can
> specify -DLLVM_BUILD_EXTERNAL_COMPILER_RT=On, which will configure
> compiler-rt using the just-built clang after clang is built.
>
I thought the BUILD_EXTERNAL variables were for use when projects were not
embedded within the llvm source tree (mostly in use by Takumi's flat
buildbots that checout the top-level project without embedding, say, clang
or compiler-rt within the llvm source tree)?

>
> 2) The new way, is to place compiler-rt under LLVM/runtimes. In this path
> the build system will automatically build with the just-built compiler.
> This path also splits compiler-rt into two separate build steps, one that
> configures and builds the builtins with the just-built compiler, and a
> second that configures and builds the sanitizer libraries.
>
Huh, OK - could someone remove the legacy format, then? If it's a trap.

That said, I tried putting compiler-rt in runtimes instead of projects and
I got a bunch of cmake errors starting with:

CMake Error at
/usr/local/google/home/blaikie/dev/llvm/build/clang/debug/split/notypes/nostandalone/lib/cmake/llvm/AddLLVM.cmake:1174
(add_dependencies):
  The dependency target "GotsanRuntimeCheck" of target
"check-runtimes" does
  not exist.
Call Stack (most recent call first):
  CMakeLists.txt:110 (add_lit_target)

Any ideas?

>
> The second path also works for many (but not all) of our other runtime
> library projects. I know it works for libcxx, libcxxabi, and
> libunwind. Petr Hosek (CC'd) has also been working on support for
> multi-arch builtin and runtime library builds so that you can generate full
> cross-compilers from a single cmake invocation.
>
> -Chris
>
>
> On Mar 8, 2017, at 2:35 PM, David Blaikie via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>
>
> On Wed, Mar 8, 2017 at 2:03 PM Sterling Augustine <saugustine at
google.com>
> wrote:
>
> Yes, this is a aspect of the larger problem that clang bootstrap
doesn't
> work for a cross-compiler. The build (mostly?) assumes that host==target
> during the build of clang itself, and then if you want another architecture
> also, you run a second build of the target libraries, and manually merge
> the trees.
>
>
> I kind of roughly follow that, but not too well.
>
>
> If you think about compiler-rt as being compiled for the target rather
> than the host, the problem you describe here is exactly the same one, and
> we have been getting lucky.
>
>
> Sure - if a PPC clang is being built from an x86 host, how would
> compiler-rt be built (OK, it could be built with the just-built clang,
> which it isn't at the moment) and tested (can't really be tested
because
> the host can't run PPC binaries).
>
>
> At the moment, the blaze builds of clang do exactly the procedure
> described above, so this hasn't been a terrible problem for Google, but
I
> do think it is something that should be fixed (I'm working on another
> aspect of compiler-rt bringup at the moment, so won't solve this in the
> immediate future.)
>
>
> Rightio
>
>
>
> gnu systems have a make variable, "CC_FOR_TARGET" that addresses
this
> problem. I imagine llvm should adopt a similar mechanism inside cmake.
>
>
> Not sure I follow on the need/use of CC_FOR_TARGET compared to using the
> just-built clang as the CC_FOR_TARGET (which it seems we have some plumbing
> for already - the just-built clang is used for building the compiler-rt
> tests, but not for building the library. I /think/ it should be used for
> both)
>
> - Dave
>
>
>
> On Wed, Mar 8, 2017 at 1:54 PM, David Blaikie <dblaikie at gmail.com>
wrote:
>
> I stumbled across what seems to be a bug (to me) in the compiler-rt build:
>
> The compiler-rt libraries themselves are built with the host compiler
> while the tests are built and then linked with the just-built clang.
>
> It was my understanding that the goal/intent/need was to have the
> compiler-rt library build with the just-built clang? Did I misunderstand
> that?*
>
> Sterling: Chandler seemed to think you might be interested in this issue
&
> possibly addressing it given you're working on compiler-rt bring-up?
It'd
> probably be useful to have compiler-rt built with the just-built clang for
> performance reasons.
>
> Evgeniy - not sure if you're interested in this or have much context?
Know
> if this is right/wrong/neutral, etc?
>
> * reasons include performance, ABI compatibility, etc (I thought this was
> necessary for correctness in some way) - also, otherwise it seems excessive
> to hold up the whole build on waiting for just-built clang to finish, then
> use that to compile some tests. (well, I realize some of the tests are
> end-to-end, so they do need the just-built compiler)
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
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> On Mar 8, 2017, at 3:16 PM, David Blaikie <dblaikie at gmail.com>
wrote:
> 
> 
> 
> On Wed, Mar 8, 2017 at 2:55 PM Chris Bieneman <beanz at apple.com
<mailto:beanz at apple.com>> wrote:
> David,
> 
> This is an area that has had a lot of development over the last two years.
> 
> There are two supported ways in the LLVM build system to build compiler-rt
with the just-built compiler.
> 
> 1) The legacy way is for if compiler-rt is under LLVM/projects. You can
specify -DLLVM_BUILD_EXTERNAL_COMPILER_RT=On, which will configure compiler-rt
using the just-built clang after clang is built.
> 
> I thought the BUILD_EXTERNAL variables were for use when projects were not
embedded within the llvm source tree (mostly in use by Takumi's flat
buildbots that checout the top-level project without embedding, say, clang or
compiler-rt within the llvm source tree)?
You are confusing this with the similarly named
LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR variables.
>  
> 
> 2) The new way, is to place compiler-rt under LLVM/runtimes. In this path
the build system will automatically build with the just-built compiler. This
path also splits compiler-rt into two separate build steps, one that configures
and builds the builtins with the just-built compiler, and a second that
configures and builds the sanitizer libraries.
> 
> Huh, OK - could someone remove the legacy format, then? If it's a trap.
I'm not sure the new path is fully supported in every workflow, so removing
it seems like a not great idea at the moment.
> 
> That said, I tried putting compiler-rt in runtimes instead of projects and
I got a bunch of cmake errors starting with:
> 
> CMake Error at
/usr/local/google/home/blaikie/dev/llvm/build/clang/debug/split/notypes/nostandalone/lib/cmake/llvm/AddLLVM.cmake:1174
(add_dependencies):
>   The dependency target "GotsanRuntimeCheck" of target
"check-runtimes" does
>   not exist.
> Call Stack (most recent call first):
>   CMakeLists.txt:110 (add_lit_target)
> 
> Any ideas?
I have never encountered that issue. It looks like the tsan test code is out of
sync. If you go into tsan/test/CMakeLists.txt and on Line 2 add this to the if
statement "AND TARGET GotsanRuntimeCheck" that should fix the issue.

-Chris
>  
> 
> The second path also works for many (but not all) of our other runtime
library projects. I know it works for libcxx, libcxxabi, and libunwind. Petr
Hosek (CC'd) has also been working on support for multi-arch builtin and
runtime library builds so that you can generate full cross-compilers from a
single cmake invocation.
> 
> -Chris
> 
> 
> 
>> On Mar 8, 2017, at 2:35 PM, David Blaikie via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
> 
>> 
>> 
>> On Wed, Mar 8, 2017 at 2:03 PM Sterling Augustine <saugustine at
google.com <mailto:saugustine at google.com>> wrote:
>> Yes, this is a aspect of the larger problem that clang bootstrap
doesn't work for a cross-compiler. The build (mostly?) assumes that
host==target during the build of clang itself, and then if you want another
architecture also, you run a second build of the target libraries, and manually
merge the trees.
>> 
>> I kind of roughly follow that, but not too well.
>>  
>> If you think about compiler-rt as being compiled for the target rather
than the host, the problem you describe here is exactly the same one, and we
have been getting lucky.
>> 
>> Sure - if a PPC clang is being built from an x86 host, how would
compiler-rt be built (OK, it could be built with the just-built clang, which it
isn't at the moment) and tested (can't really be tested because the host
can't run PPC binaries).
>>  
>> At the moment, the blaze builds of clang do exactly the procedure
described above, so this hasn't been a terrible problem for Google, but I do
think it is something that should be fixed (I'm working on another aspect of
compiler-rt bringup at the moment, so won't solve this in the immediate
future.)
>> 
>> Rightio
>>  
>> 
>> gnu systems have a make variable, "CC_FOR_TARGET" that
addresses this problem. I imagine llvm should adopt a similar mechanism inside
cmake.
>> 
>> Not sure I follow on the need/use of CC_FOR_TARGET compared to using
the just-built clang as the CC_FOR_TARGET (which it seems we have some plumbing
for already - the just-built clang is used for building the compiler-rt tests,
but not for building the library. I /think/ it should be used for both)
>> 
>> - Dave
>>  
>> 
>> On Wed, Mar 8, 2017 at 1:54 PM, David Blaikie <dblaikie at gmail.com
<mailto:dblaikie at gmail.com>> wrote:
>> I stumbled across what seems to be a bug (to me) in the compiler-rt
build:
>> 
>> The compiler-rt libraries themselves are built with the host compiler
while the tests are built and then linked with the just-built clang.
>> 
>> It was my understanding that the goal/intent/need was to have the
compiler-rt library build with the just-built clang? Did I misunderstand that?*
>> 
>> Sterling: Chandler seemed to think you might be interested in this
issue & possibly addressing it given you're working on compiler-rt
bring-up? It'd probably be useful to have compiler-rt built with the
just-built clang for performance reasons.
>> 
>> Evgeniy - not sure if you're interested in this or have much
context? Know if this is right/wrong/neutral, etc?
>> 
>> * reasons include performance, ABI compatibility, etc (I thought this
was necessary for correctness in some way) - also, otherwise it seems excessive
to hold up the whole build on waiting for just-built clang to finish, then use
that to compile some tests. (well, I realize some of the tests are end-to-end,
so they do need the just-built compiler)
>> 
> 
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> 
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On Wed, Mar 8, 2017 at 3:23 PM Chris Bieneman <beanz at apple.com> wrote:
> On Mar 8, 2017, at 3:16 PM, David Blaikie <dblaikie at gmail.com>
wrote:
>
>
>
> On Wed, Mar 8, 2017 at 2:55 PM Chris Bieneman <beanz at apple.com>
wrote:
>
> David,
>
> This is an area that has had a lot of development over the last two years.
>
> There are two supported ways in the LLVM build system to build compiler-rt
> with the just-built compiler.
>
> 1) The legacy way is for if compiler-rt is under LLVM/projects. You can
> specify -DLLVM_BUILD_EXTERNAL_COMPILER_RT=On, which will configure
> compiler-rt using the just-built clang after clang is built.
>
>
> I thought the BUILD_EXTERNAL variables were for use when projects were not
> embedded within the llvm source tree (mostly in use by Takumi's flat
> buildbots that checout the top-level project without embedding, say, clang
> or compiler-rt within the llvm source tree)?
>
>
> You are confusing this with the similarly
> named LLVM_EXTERNAL_${nameUPPER}_SOURCE_DIR variables.
>
Ah, right - indeed.
>
> 2) The new way, is to place compiler-rt under LLVM/runtimes. In this path
> the build system will automatically build with the just-built compiler.
> This path also splits compiler-rt into two separate build steps, one that
> configures and builds the builtins with the just-built compiler, and a
> second that configures and builds the sanitizer libraries.
>
>
> Huh, OK - could someone remove the legacy format, then? If it's a trap.
>
>
> I'm not sure the new path is fully supported in every workflow, so
> removing it seems like a not great idea at the moment.
>
>
> That said, I tried putting compiler-rt in runtimes instead of projects and
> I got a bunch of cmake errors starting with:
>
> CMake Error at
>
/usr/local/google/home/blaikie/dev/llvm/build/clang/debug/split/notypes/nostandalone/lib/cmake/llvm/AddLLVM.cmake:1174
> (add_dependencies):
>   The dependency target "GotsanRuntimeCheck" of target
"check-runtimes"
> does
>   not exist.
> Call Stack (most recent call first):
>   CMakeLists.txt:110 (add_lit_target)
>
> Any ideas?
>
>
> I have never encountered that issue. It looks like the tsan test code is
> out of sync. If you go into tsan/test/CMakeLists.txt and on Line 2 add this
> to the if statement "AND TARGET GotsanRuntimeCheck" that should
fix the
> issue.
>
Hrm - not sure which CMakeLists.txt you're referring to? In my
runtimes/compiler-rt/lib/tsan/tests/CMakeLists.txt the first few lines are:

include_directories(../rtl)

add_custom_target(TsanUnitTests)
set_target_properties(TsanUnitTests PROPERTIES
  FOLDER "TSan unittests")

no if condition I could modify?

>
> -Chris
>
>
>
>
> The second path also works for many (but not all) of our other runtime
> library projects. I know it works for libcxx, libcxxabi, and
> libunwind. Petr Hosek (CC'd) has also been working on support for
> multi-arch builtin and runtime library builds so that you can generate full
> cross-compilers from a single cmake invocation.
>
> -Chris
>
>
> On Mar 8, 2017, at 2:35 PM, David Blaikie via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>
>
> On Wed, Mar 8, 2017 at 2:03 PM Sterling Augustine <saugustine at
google.com>
> wrote:
>
> Yes, this is a aspect of the larger problem that clang bootstrap
doesn't
> work for a cross-compiler. The build (mostly?) assumes that host==target
> during the build of clang itself, and then if you want another architecture
> also, you run a second build of the target libraries, and manually merge
> the trees.
>
>
> I kind of roughly follow that, but not too well.
>
>
> If you think about compiler-rt as being compiled for the target rather
> than the host, the problem you describe here is exactly the same one, and
> we have been getting lucky.
>
>
> Sure - if a PPC clang is being built from an x86 host, how would
> compiler-rt be built (OK, it could be built with the just-built clang,
> which it isn't at the moment) and tested (can't really be tested
because
> the host can't run PPC binaries).
>
>
> At the moment, the blaze builds of clang do exactly the procedure
> described above, so this hasn't been a terrible problem for Google, but
I
> do think it is something that should be fixed (I'm working on another
> aspect of compiler-rt bringup at the moment, so won't solve this in the
> immediate future.)
>
>
> Rightio
>
>
>
> gnu systems have a make variable, "CC_FOR_TARGET" that addresses
this
> problem. I imagine llvm should adopt a similar mechanism inside cmake.
>
>
> Not sure I follow on the need/use of CC_FOR_TARGET compared to using the
> just-built clang as the CC_FOR_TARGET (which it seems we have some plumbing
> for already - the just-built clang is used for building the compiler-rt
> tests, but not for building the library. I /think/ it should be used for
> both)
>
> - Dave
>
>
>
> On Wed, Mar 8, 2017 at 1:54 PM, David Blaikie <dblaikie at gmail.com>
wrote:
>
> I stumbled across what seems to be a bug (to me) in the compiler-rt build:
>
> The compiler-rt libraries themselves are built with the host compiler
> while the tests are built and then linked with the just-built clang.
>
> It was my understanding that the goal/intent/need was to have the
> compiler-rt library build with the just-built clang? Did I misunderstand
> that?*
>
> Sterling: Chandler seemed to think you might be interested in this issue
&
> possibly addressing it given you're working on compiler-rt bring-up?
It'd
> probably be useful to have compiler-rt built with the just-built clang for
> performance reasons.
>
> Evgeniy - not sure if you're interested in this or have much context?
Know
> if this is right/wrong/neutral, etc?
>
> * reasons include performance, ABI compatibility, etc (I thought this was
> necessary for correctness in some way) - also, otherwise it seems excessive
> to hold up the whole build on waiting for just-built clang to finish, then
> use that to compile some tests. (well, I realize some of the tests are
> end-to-end, so they do need the just-built compiler)
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
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