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Teresa Johnson via llvm-dev

2018-May-09 17:06 UTC

[llvm-dev] lld + ThinLTO + fprofile-generate causes duplicate symbol errors

Adding Peter to comment on the linker resolution issue.
>From adding save-temps, it looks like lld and gold are giving differentresolutions to the symbols, which is presumably creating this issue:

(first file is with lld and second is with gold)

$ diff a.out.resolution.txt gold/
4c4
< -r=a.o,__llvm_profile_raw_version,plx
---> -r=a.o,__llvm_profile_raw_version,l8,9c8,9
< -r=b.o,__llvm_profile_raw_version,x
< -r=b.o,__llvm_profile_filename,x
---> -r=b.o,__llvm_profile_raw_version,l
> -r=b.o,__llvm_profile_filename,l
I.e. with lld they are all marked as exported.

Peter, any ideas?

Teresa


On Wed, May 9, 2018 at 9:52 AM Teresa Johnson <tejohnson at google.com>
wrote:
> Sorry, operator error. I can reproduce now. Interestingly, this does not
> reproduce using gold, and they utilize the same underlying LTO API. Let me
> dig a little using save-temps and see where they diverge.
> Teresa
>
> On Wed, May 9, 2018 at 9:28 AM Pirama Arumuga Nainar <pirama at
google.com>
> wrote:
>
>> LLD revision is r331862.  To add, I had initially tried it on r328903,
>> which also reproduced the issue.
>>
>> On Wed, May 9, 2018 at 9:26 AM Pirama Arumuga Nainar <pirama at
google.com>
>> wrote:
>>
>>> Hi Teresa,
>>>
>>> Thanks for looking into this.  I hadn't initially tried ToT,
but it
>>> reproduces in ToT as well when I tried.
>>>
>>> $ ./clang --version
>>>
>>> clang version 7.0.0 (trunk 331879) (llvm/trunk 331888)
>>> Target: x86_64-unknown-linux-gnu
>>> Thread model: posix
>>> InstalledDir: /ssd2/pirama/llvm-upstream/llvm-release/bin/.
>>>
>>> $ ./ld.lld --version
>>> LLD 7.0.0 (https://git.llvm.org/git/lld.git
dc4977e104c7f33758ac6119d1528aafcd8a94dc) (compatible with GNU linkers)
>>>
>>>
>>> On Wed, May 9, 2018 at 6:44 AM Teresa Johnson <tejohnson at
google.com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Wed, May 9, 2018 at 6:43 AM Teresa Johnson <tejohnson at
google.com>
>>>> wrote:
>>>>
>>>>> Hi Pirama,
>>>>>
>>>>> I can't reproduce with either lld or gold, using a
compiler built from
>>>>> head. What version is your clang?
>>>>>
>>>> (and your lld)
>>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> Teresa
>>>>>
>>>>> On Tue, May 8, 2018 at 7:50 PM Pirama Arumuga Nainar via
llvm-dev <
>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>>> The duplicate symbol errors are for
__llvm_profile_filename and __llvm_profile_raw_version.
>>>>>> IIUC, these are supposed to be weak symbols but Thin
LTO seems to break
>>>>>> this in some way.  This does't happen with gold or
no LTO or full
>>>>>> LTO.
>>>>>>
>>>>>> $ cat > a.c
>>>>>> extern int foo();
>>>>>>
>>>>>> int main() {
>>>>>>   return foo();
>>>>>> }
>>>>>>
>>>>>> $ cat > b.c
>>>>>> int foo() {
>>>>>>   return 0;
>>>>>> }
>>>>>>
>>>>>> $ clang a.c -fprofile-generate -flto=thin -c
>>>>>> $ clang b.c -fprofile-generate -flto=thin -c
>>>>>> $ clang a.o b.o -fprofile-generate -flto=thin
-fuse-ld=lld
>>>>>> ld.lld: error: duplicate symbol:
__llvm_profile_filename
>>>>>> >>> defined at a.c
>>>>>> >>>           
lto.tmp:(__llvm_profile_filename)
>>>>>> >>> defined at b.c
>>>>>> >>>           
lto.tmp:(.rodata.__llvm_profile_filename+0x0)
>>>>>>
>>>>>> ld.lld: error: duplicate symbol:
__llvm_profile_raw_version
>>>>>> >>> defined at a.c
>>>>>> >>>           
lto.tmp:(__llvm_profile_raw_version)
>>>>>> >>> defined at b.c
>>>>>> >>>           
lto.tmp:(.rodata.__llvm_profile_raw_version+0x0)
>>>>>> clang-7: error: linker command failed with exit code 1
(use -v to see
>>>>>> invocation)
>>>>>> Makefile:10: recipe for target 'a.out' failed
>>>>>> make: *** [a.out] Error 1
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Teresa Johnson |  Software Engineer |  tejohnson at
google.com |
>>>>>  408-460-2413
>>>>>
>>>>
>>>>
>>>> --
>>>> Teresa Johnson |  Software Engineer |  tejohnson at google.com
|
>>>>  408-460-2413
>>>>
>>>
>
> --
> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>  408-460-2413
>

-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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Peter Collingbourne via llvm-dev

2018-May-09 18:26 UTC

head link

[llvm-dev] lld + ThinLTO + fprofile-generate causes duplicate symbol errors

The problem is that ThinLTO is not dropping the non-prevailing definitions,
and they end up being emitted into the object file for b.o.

$ ../ra/bin/llvm-dis -o - b.o0.0.preopt.bc | grep __llvm_prof
$__llvm_profile_raw_version = comdat any
$__llvm_profile_filename = comdat any
@__llvm_profile_raw_version = constant i64 72057594037927940, comdat
@__llvm_profile_filename = constant [19 x i8]
c"default_%m.profraw\00",
comdat

lld ignores comdats in LTO object files because it expects all comdats to
have already been resolved. So we see this error.

We are supposed to drop non-prevailing symbols here, but for some reason we
do it only for weak symbols. That's not correct in ELF where comdat symbols
can be both strong and non-prevailing.
http://llvm-cs.pcc.me.uk/lib/LTO/LTO.cpp#290

This patch fixes the reproducer but it leads to other test failures that
would need to be looked at.

diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 7e8b9b3c6390..ee11d07d6b8e 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -287,7 +287,7 @@ static void thinLTOResolveWeakForLinkerGUID(
         recordNewLinkage) {
   for (auto &S : GVSummaryList) {
     GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
-    if (!GlobalValue::isWeakForLinker(OriginalLinkage))
+    if (GlobalValue::isLocalLinkage(OriginalLinkage))
       continue;
     // We need to emit only one of these. The prevailing module will keep
it,
     // but turned into a weak, while the others will drop it when possible.
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp
b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 246d75caefa2..61790c9fc435 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -765,7 +765,7 @@ void llvm::thinLTOResolveWeakForLinkerModule(
       return;
     }

-    if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
+    if (GlobalValue::isLocalLinkage(GV.getLinkage()))
       return;
     // Check for a non-prevailing def that has interposable linkage
     // (e.g. non-odr weak or linkonce). In that case we can't simply

Peter

On Wed, May 9, 2018 at 10:06 AM, Teresa Johnson <tejohnson at google.com>
wrote:
> Adding Peter to comment on the linker resolution issue.
>
> From adding save-temps, it looks like lld and gold are giving different
> resolutions to the symbols, which is presumably creating this issue:
>
> (first file is with lld and second is with gold)
>
> $ diff a.out.resolution.txt gold/
> 4c4
> < -r=a.o,__llvm_profile_raw_version,plx
> ---
> > -r=a.o,__llvm_profile_raw_version,l
> 8,9c8,9
> < -r=b.o,__llvm_profile_raw_version,x
> < -r=b.o,__llvm_profile_filename,x
> ---
> > -r=b.o,__llvm_profile_raw_version,l
> > -r=b.o,__llvm_profile_filename,l
>
> I.e. with lld they are all marked as exported.
>
> Peter, any ideas?
>
> Teresa
>
>
> On Wed, May 9, 2018 at 9:52 AM Teresa Johnson <tejohnson at
google.com>
> wrote:
>
>> Sorry, operator error. I can reproduce now. Interestingly, this does
not
>> reproduce using gold, and they utilize the same underlying LTO API. Let
me
>> dig a little using save-temps and see where they diverge.
>> Teresa
>>
>> On Wed, May 9, 2018 at 9:28 AM Pirama Arumuga Nainar <pirama at
google.com>
>> wrote:
>>
>>> LLD revision is r331862.  To add, I had initially tried it on
r328903,
>>> which also reproduced the issue.
>>>
>>> On Wed, May 9, 2018 at 9:26 AM Pirama Arumuga Nainar <pirama at
google.com>
>>> wrote:
>>>
>>>> Hi Teresa,
>>>>
>>>> Thanks for looking into this.  I hadn't initially tried
ToT, but it
>>>> reproduces in ToT as well when I tried.
>>>>
>>>> $ ./clang --version
>>>>
>>>> clang version 7.0.0 (trunk 331879) (llvm/trunk 331888)
>>>> Target: x86_64-unknown-linux-gnu
>>>> Thread model: posix
>>>> InstalledDir: /ssd2/pirama/llvm-upstream/llvm-release/bin/.
>>>>
>>>> $ ./ld.lld --version
>>>> LLD 7.0.0 (https://git.llvm.org/git/lld.git
dc4977e104c7f33758ac6119d1528aafcd8a94dc) (compatible with GNU linkers)
>>>>
>>>>
>>>> On Wed, May 9, 2018 at 6:44 AM Teresa Johnson <tejohnson at
google.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Wed, May 9, 2018 at 6:43 AM Teresa Johnson <tejohnson
at google.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Pirama,
>>>>>>
>>>>>> I can't reproduce with either lld or gold, using a
compiler built
>>>>>> from head. What version is your clang?
>>>>>>
>>>>> (and your lld)
>>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Teresa
>>>>>>
>>>>>> On Tue, May 8, 2018 at 7:50 PM Pirama Arumuga Nainar
via llvm-dev <
>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>
>>>>>>> The duplicate symbol errors are for
__llvm_profile_filename and
>>>>>>> __llvm_profile_raw_version.  IIUC, these are
supposed to be weak
>>>>>>> symbols but Thin LTO seems to break this in some
way.  This does't
>>>>>>> happen with gold or no LTO or full LTO.
>>>>>>>
>>>>>>> $ cat > a.c
>>>>>>> extern int foo();
>>>>>>>
>>>>>>> int main() {
>>>>>>>   return foo();
>>>>>>> }
>>>>>>>
>>>>>>> $ cat > b.c
>>>>>>> int foo() {
>>>>>>>   return 0;
>>>>>>> }
>>>>>>>
>>>>>>> $ clang a.c -fprofile-generate -flto=thin -c
>>>>>>> $ clang b.c -fprofile-generate -flto=thin -c
>>>>>>> $ clang a.o b.o -fprofile-generate -flto=thin
-fuse-ld=lld
>>>>>>> ld.lld: error: duplicate symbol:
__llvm_profile_filename
>>>>>>> >>> defined at a.c
>>>>>>> >>>           
lto.tmp:(__llvm_profile_filename)
>>>>>>> >>> defined at b.c
>>>>>>> >>>           
lto.tmp:(.rodata.__llvm_profile_filename+0x0)
>>>>>>>
>>>>>>> ld.lld: error: duplicate symbol:
__llvm_profile_raw_version
>>>>>>> >>> defined at a.c
>>>>>>> >>>           
lto.tmp:(__llvm_profile_raw_version)
>>>>>>> >>> defined at b.c
>>>>>>> >>>           
lto.tmp:(.rodata.__llvm_profile_raw_version+0x0)
>>>>>>> clang-7: error: linker command failed with exit
code 1 (use -v to
>>>>>>> see invocation)
>>>>>>> Makefile:10: recipe for target 'a.out'
failed
>>>>>>> make: *** [a.out] Error 1
>>>>>>> _______________________________________________
>>>>>>> LLVM Developers mailing list
>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Teresa Johnson |  Software Engineer |  tejohnson at
google.com |
>>>>>>  408-460-2413
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Teresa Johnson |  Software Engineer |  tejohnson at
google.com |
>>>>>  408-460-2413
>>>>>
>>>>
>>
>> --
>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>  408-460-2413
>>
>
>
> --
> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>  408-460-2413
>


-- 
-- 
Peter
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Pirama Arumuga Nainar via llvm-dev

2018-May-11 19:24 UTC

head link

[llvm-dev] lld + ThinLTO + fprofile-generate causes duplicate symbol errors

Thanks Peter, your patch does fix the reproducer.  I filed
https://bugs.llvm.org/show_bug.cgi?id=37422 to track this bug.  I have no
clue on how to resolve the tests - whether further cleanup is required in
the code or in the tests.  But if Teresa or you cannot get to it, I can,
with some help, take a crack at fixing the tests.

On Wed, May 9, 2018 at 11:26 AM Peter Collingbourne <peter at pcc.me.uk>
wrote:
> The problem is that ThinLTO is not dropping the non-prevailing
> definitions, and they end up being emitted into the object file for b.o.
>
> $ ../ra/bin/llvm-dis -o - b.o0.0.preopt.bc | grep __llvm_prof
> $__llvm_profile_raw_version = comdat any
> $__llvm_profile_filename = comdat any
> @__llvm_profile_raw_version = constant i64 72057594037927940, comdat
> @__llvm_profile_filename = constant [19 x i8]
c"default_%m.profraw\00",
> comdat
>
> lld ignores comdats in LTO object files because it expects all comdats to
> have already been resolved. So we see this error.
>
> We are supposed to drop non-prevailing symbols here, but for some reason
> we do it only for weak symbols. That's not correct in ELF where comdat
> symbols can be both strong and non-prevailing.
> http://llvm-cs.pcc.me.uk/lib/LTO/LTO.cpp#290
>
> This patch fixes the reproducer but it leads to other test failures that
> would need to be looked at.
>
> diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
> index 7e8b9b3c6390..ee11d07d6b8e 100644
> --- a/llvm/lib/LTO/LTO.cpp
> +++ b/llvm/lib/LTO/LTO.cpp
> @@ -287,7 +287,7 @@ static void thinLTOResolveWeakForLinkerGUID(
>          recordNewLinkage) {
>    for (auto &S : GVSummaryList) {
>      GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
> -    if (!GlobalValue::isWeakForLinker(OriginalLinkage))
> +    if (GlobalValue::isLocalLinkage(OriginalLinkage))
>        continue;
>      // We need to emit only one of these. The prevailing module will keep
> it,
>      // but turned into a weak, while the others will drop it when
> possible.
> diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp
> b/llvm/lib/Transforms/IPO/FunctionImport.cpp
> index 246d75caefa2..61790c9fc435 100644
> --- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
> +++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
> @@ -765,7 +765,7 @@ void llvm::thinLTOResolveWeakForLinkerModule(
>        return;
>      }
>
> -    if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
> +    if (GlobalValue::isLocalLinkage(GV.getLinkage()))
>        return;
>      // Check for a non-prevailing def that has interposable linkage
>      // (e.g. non-odr weak or linkonce). In that case we can't simply
>
> Peter
>
> On Wed, May 9, 2018 at 10:06 AM, Teresa Johnson <tejohnson at
google.com>
> wrote:
>
>> Adding Peter to comment on the linker resolution issue.
>>
>> From adding save-temps, it looks like lld and gold are giving different
>> resolutions to the symbols, which is presumably creating this issue:
>>
>> (first file is with lld and second is with gold)
>>
>> $ diff a.out.resolution.txt gold/
>> 4c4
>> < -r=a.o,__llvm_profile_raw_version,plx
>> ---
>> > -r=a.o,__llvm_profile_raw_version,l
>> 8,9c8,9
>> < -r=b.o,__llvm_profile_raw_version,x
>> < -r=b.o,__llvm_profile_filename,x
>> ---
>> > -r=b.o,__llvm_profile_raw_version,l
>> > -r=b.o,__llvm_profile_filename,l
>>
>> I.e. with lld they are all marked as exported.
>>
>> Peter, any ideas?
>>
>> Teresa
>>
>>
>> On Wed, May 9, 2018 at 9:52 AM Teresa Johnson <tejohnson at
google.com>
>> wrote:
>>
>>> Sorry, operator error. I can reproduce now. Interestingly, this
does not
>>> reproduce using gold, and they utilize the same underlying LTO API.
Let me
>>> dig a little using save-temps and see where they diverge.
>>> Teresa
>>>
>>> On Wed, May 9, 2018 at 9:28 AM Pirama Arumuga Nainar <pirama at
google.com>
>>> wrote:
>>>
>>>> LLD revision is r331862.  To add, I had initially tried it on
r328903,
>>>> which also reproduced the issue.
>>>>
>>>> On Wed, May 9, 2018 at 9:26 AM Pirama Arumuga Nainar <pirama
at google.com>
>>>> wrote:
>>>>
>>>>> Hi Teresa,
>>>>>
>>>>> Thanks for looking into this.  I hadn't initially tried
ToT, but it
>>>>> reproduces in ToT as well when I tried.
>>>>>
>>>>> $ ./clang --version
>>>>>
>>>>> clang version 7.0.0 (trunk 331879) (llvm/trunk 331888)
>>>>> Target: x86_64-unknown-linux-gnu
>>>>> Thread model: posix
>>>>> InstalledDir: /ssd2/pirama/llvm-upstream/llvm-release/bin/.
>>>>>
>>>>> $ ./ld.lld --version
>>>>> LLD 7.0.0 (https://git.llvm.org/git/lld.git
dc4977e104c7f33758ac6119d1528aafcd8a94dc) (compatible with GNU linkers)
>>>>>
>>>>>
>>>>> On Wed, May 9, 2018 at 6:44 AM Teresa Johnson <tejohnson
at google.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, May 9, 2018 at 6:43 AM Teresa Johnson
<tejohnson at google.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Hi Pirama,
>>>>>>>
>>>>>>> I can't reproduce with either lld or gold,
using a compiler built
>>>>>>> from head. What version is your clang?
>>>>>>>
>>>>>> (and your lld)
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Teresa
>>>>>>>
>>>>>>> On Tue, May 8, 2018 at 7:50 PM Pirama Arumuga
Nainar via llvm-dev <
>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>
>>>>>>>> The duplicate symbol errors are for
__llvm_profile_filename and __llvm_profile_raw_version.
>>>>>>>> IIUC, these are supposed to be weak symbols but
Thin LTO seems to break
>>>>>>>> this in some way.  This does't happen with
gold or no LTO or full
>>>>>>>> LTO.
>>>>>>>>
>>>>>>>> $ cat > a.c
>>>>>>>> extern int foo();
>>>>>>>>
>>>>>>>> int main() {
>>>>>>>>   return foo();
>>>>>>>> }
>>>>>>>>
>>>>>>>> $ cat > b.c
>>>>>>>> int foo() {
>>>>>>>>   return 0;
>>>>>>>> }
>>>>>>>>
>>>>>>>> $ clang a.c -fprofile-generate -flto=thin -c
>>>>>>>> $ clang b.c -fprofile-generate -flto=thin -c
>>>>>>>> $ clang a.o b.o -fprofile-generate -flto=thin
-fuse-ld=lld
>>>>>>>> ld.lld: error: duplicate symbol:
__llvm_profile_filename
>>>>>>>> >>> defined at a.c
>>>>>>>> >>>           
lto.tmp:(__llvm_profile_filename)
>>>>>>>> >>> defined at b.c
>>>>>>>> >>>           
lto.tmp:(.rodata.__llvm_profile_filename+0x0)
>>>>>>>>
>>>>>>>> ld.lld: error: duplicate symbol:
__llvm_profile_raw_version
>>>>>>>> >>> defined at a.c
>>>>>>>> >>>           
lto.tmp:(__llvm_profile_raw_version)
>>>>>>>> >>> defined at b.c
>>>>>>>> >>>           
lto.tmp:(.rodata.__llvm_profile_raw_version+0x0)
>>>>>>>> clang-7: error: linker command failed with exit
code 1 (use -v to
>>>>>>>> see invocation)
>>>>>>>> Makefile:10: recipe for target 'a.out'
failed
>>>>>>>> make: *** [a.out] Error 1
>>>>>>>> _______________________________________________
>>>>>>>> LLVM Developers mailing list
>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Teresa Johnson |  Software Engineer |  tejohnson at
google.com |
>>>>>>>  408-460-2413
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Teresa Johnson |  Software Engineer |  tejohnson at
google.com |
>>>>>>  408-460-2413
>>>>>>
>>>>>
>>>
>>> --
>>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>>  408-460-2413
>>>
>>
>>
>> --
>> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
>>  408-460-2413
>>
>
>
>
> --
> --
> Peter
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