[llvm-dev] distributed thinlto usage
David Callahan via llvm-dev
llvm-dev at lists.llvm.org
Wed Jan 9 08:13:08 PST 2019
Thanks very much , that did resolve my problem.
From: Teresa Johnson <tejohnson at google.com>
Date: Wednesday, January 9, 2019 at 7:43 AM
To: David Callahan <dcallahan at fb.com>
Cc: LLVM Dev Mailing list <llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] distributed thinlto usage
Mystery solved - the short answer is to add "-Xclang -fno-lto-unit" to your compile steps (-c -flto=thin). I had forgotten that we add this for our internal distributed builds. Another option would be to add "-Wl,-plugin-opt,obj-path=astar.o" to the thin link step, and add the resulting (native) astar.o file to the final link.
I am working on getting the default changed (D53890/D53891), since this is only needed for CFI [1], but currently by default each module is split into two - a regular LTO module containing vtable defs and a thin LTO module containing the rest. This is required by CFI so that the vtables can be globally laid out via regular LTO. If you don't disable this splitting (via "-Xclang -fno-lto-unit"), then you need to capture the result of this regular LTO portion via the obj-path plugin option and link it as well. However, unless you plan to do CFI this is just giving your builds extra unnecessary overhead (which is why the default will change).
[1] Also currently for whole program devirtualization which is enabled for CFI, or separately via options - although I have a patch out for review to do WPD with ThinLTO alone (D55153).
Teresa
On Tue, Jan 8, 2019 at 5:28 PM Teresa Johnson <tejohnson at google.com<mailto:tejohnson at google.com>> wrote:
Ok thanks for checking. I'll try to repro tomorrow morning probably and get back. Teresa
On Tue, Jan 8, 2019, 5:03 PM David Callahan <dcallahan at fb.com<mailto:dcallahan at fb.com>> wrote:
Fails with gold too:
Library-native.o:Library.cpp:regway: error: undefined reference to 'vtable for regwayobj'
/home/dcallahan/fbsource/fbcode/third-party-buck/platform007/tools/binutils/bin/gold/ld: the vtable symbol may be undefined because the class is missing its key function
clang-8: error: linker command failed with exit code 1 (use -v to see invocation)
From: Teresa Johnson <tejohnson at google.com<mailto:tejohnson at google.com>>
Date: Tuesday, January 8, 2019 at 4:57 PM
To: David Callahan <dcallahan at fb.com<mailto:dcallahan at fb.com>>
Cc: LLVM Dev Mailing list <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Subject: Re: [llvm-dev] distributed thinlto usage
On Tue, Jan 8, 2019 at 4:36 PM David Callahan <dcallahan at fb.com<mailto:dcallahan at fb.com>> wrote:
Thanks Teresa
Yes it is astar, happen to send a tar of the sources but they are just copies from the spec distribution
The ld command is:
GNU ld (GNU Binutils) 2.29.1
Could you try with either a recent gold or lld to see if it still reproduces? We don't test llvm LTO with GNU ld, so I can't be sure there are no issues there.
Thanks for the guidance on path names. The prefix-replace just effects the string written to the object files right? So we could post-process that file with other tools as well, correct?
Correct.
Teresa
Thanks again
--david
From: Teresa Johnson <tejohnson at google.com<mailto:tejohnson at google.com>>
Date: Tuesday, January 8, 2019 at 4:11 PM
To: David Callahan <dcallahan at fb.com<mailto:dcallahan at fb.com>>
Cc: LLVM Dev Mailing list <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Subject: Re: [llvm-dev] distributed thinlto usage
Hi David,
That looks basically right, so I am not sure offhand what is wrong. Looks like this is the astar spec binary, so I will try to repro it tomorrow morning. What linker are you using?
Note that if your link involves archives of .a files, you will want to ensure that the final native link includes only those files selected by the linker. That is output in the file given to the "-Wl,-plugin-opt,thinlto-index-only=files.out" option. What we do is use that in combination with the '-Wl,-plugin-opt,thinlto-prefix-replace=path1;path2' option to simplify the final link invocation. Specifically, if you do something like:
"-Wl,-plugin-opt,thinlto-index-only=files.out -Wl,-plugin-opt,thinlto-prefix-replace=path1;path2"
for the indexing link step, the output files from the thin link will be written to a directory tree with the original path substring "path1" replaced with "path2", and the object names in the file emitted by thinlto-index-only= ("files.out" in the above example), will have their path names adjusted to the new path as well - if your native .o files use the new path then this is a simple way of getting a list of input files for the final link, which can be passed via @files.out to gold (note the gold manpage does not document "@" but the gnu ld manpage does).
I.e. something like:
clang++ -flto=thin -O3 -c -o path1/foo.o foo.cpp
...
clang++ -flto=thin -O3 -Wl,-plugin-opt,thinlto-index-only=files.out -Wl,-plugin-opt,thinlto-prefix-replace=path1;path2" foo.o ...
clang++ -c -x ir path1/foo.o -O3 -o path2/foo.o -fthinlto-index=path2/foo.o.thinlto.bc
...
clang++ -flto=thin -O3 -o a.out @files.out
But again, that should only come into play if you are linking archives of bitcode files...
Teresa
On Tue, Jan 8, 2019 at 2:38 PM David Callahan via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
I am trying to work through the usage of thinlto for distributed builds.
Here is the simple thinlto usage, just add -flto=thin everywhere, easy:
clang++ -flto=thin -O3 -c -o CreateWay_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else CreateWay_.cpp
clang++ -flto=thin -O3 -c -o Places_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Places_.cpp
clang++ -flto=thin -O3 -c -o RegBounds_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else RegBounds_.cpp
clang++ -flto=thin -O3 -c -o RegMng_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else RegMng_.cpp
clang++ -flto=thin -O3 -c -o Way2_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Way2_.cpp
clang++ -flto=thin -O3 -c -o WayInit_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else WayInit_.cpp
clang++ -flto=thin -O3 -c -o Library.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Library.cpp
clang++ -flto=thin -O3 -c -o Random.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Random.cpp
clang++ -flto=thin -O3 -c -o Region_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Region_.cpp
clang++ -flto=thin -O3 -c -o RegWay_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else RegWay_.cpp
clang++ -flto=thin -O3 -c -o Way_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Way_.cpp
clang++ -flto=thin -O3 -o astar.thin CreateWay_.o Places_.o RegBounds_.o RegMng_.o Way2_.o WayInit_.o Library.o Random.o Region_.o RegWay_.o Way_.o
My understanding is for the distributed, you need to do the inital compiles as above,
then a special link to get the thinlto index files, then compile again to get
native files, and then a final link. This looks like the following but
it does not work:
clang++ -flto=thin -O3 -c -o CreateWay_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else CreateWay_.cpp
clang++ -flto=thin -O3 -c -o Places_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Places_.cpp
clang++ -flto=thin -O3 -c -o RegBounds_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else RegBounds_.cpp
clang++ -flto=thin -O3 -c -o RegMng_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else RegMng_.cpp
clang++ -flto=thin -O3 -c -o Way2_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Way2_.cpp
clang++ -flto=thin -O3 -c -o WayInit_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else WayInit_.cpp
clang++ -flto=thin -O3 -c -o Library.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Library.cpp
clang++ -flto=thin -O3 -c -o Random.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Random.cpp
clang++ -flto=thin -O3 -c -o Region_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Region_.cpp
clang++ -flto=thin -O3 -c -o RegWay_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else RegWay_.cpp
clang++ -flto=thin -O3 -c -o Way_.o -DSPEC_CPU -DNDEBUG -DSPEC_CPU_LITTLE_ENDIAN -Wno-dangling-else Way_.cpp
clang++ -flto=thin -O3 -o thinlto.objects -Wl,-plugin-opt,thinlto-index-only=thinlto.objects CreateWay_.o Places_.o RegBounds_.o RegMng_.o Way2_.o WayInit_.o Library.o Random.o Region_.o RegWay_.o Way_.o
clang++ -c -x ir CreateWay_.o -O3 -o CreateWay_-native.o -fthinlto-index=CreateWay_.o.thinlto.bc
clang++ -c -x ir Places_.o -O3 -o Places_-native.o -fthinlto-index=Places_.o.thinlto.bc
clang++ -c -x ir RegBounds_.o -O3 -o RegBounds_-native.o -fthinlto-index=RegBounds_.o.thinlto.bc
clang++ -c -x ir RegMng_.o -O3 -o RegMng_-native.o -fthinlto-index=RegMng_.o.thinlto.bc
clang++ -c -x ir Way2_.o -O3 -o Way2_-native.o -fthinlto-index=Way2_.o.thinlto.bc
clang++ -c -x ir WayInit_.o -O3 -o WayInit_-native.o -fthinlto-index=WayInit_.o.thinlto.bc
clang++ -c -x ir Library.o -O3 -o Library-native.o -fthinlto-index=Library.o.thinlto.bc
clang++ -c -x ir Random.o -O3 -o Random-native.o -fthinlto-index=Random.o.thinlto.bc
clang++ -c -x ir Region_.o -O3 -o Region_-native.o -fthinlto-index=Region_.o.thinlto.bc
clang++ -c -x ir RegWay_.o -O3 -o RegWay_-native.o -fthinlto-index=RegWay_.o.thinlto.bc
clang++ -c -x ir Way_.o -O3 -o Way_-native.o -fthinlto-index=Way_.o.thinlto.bc
clang++ -o astar CreateWay_-native.o Places_-native.o RegBounds_-native.o RegMng_-native.o Way2_-native.o WayInit_-native.o Library-native.o Random-native.o Region_-native.o RegWay_-native.o Way_-native.o
Library-native.o:(.data+0x0): undefined reference to `vtable for regwayobj'
clang-8: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [astar] Error 1
Did I miss a step?
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--
Teresa Johnson |
Software Engineer |
tejohnson at google.com<mailto:tejohnson at google.com> |
--
Teresa Johnson |
Software Engineer |
tejohnson at google.com<mailto:tejohnson at google.com> |
--
Teresa Johnson |
Software Engineer |
tejohnson at google.com<mailto:tejohnson at google.com> |
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