Mold fails to hide dynamic symbols

[Blendify]

Environment

OS: Ubuntu 21.10
Mold: 1.0.1 built from main (43b2a1e)
GCC: 11.2.0

I also use ninja

Introduction

Hi, recently Blender added support to our build system however we found that symbols are not being hidden when using mold compared to other linkers.

I have been trying to isolate this down to a small reproducible case
but so far have not been able to create a small project.

I can guide you through building Blender though.

Reproduction Steps

Our build instructions can be found here: https://wiki.blender.org/wiki/Building_Blender/Linux

The easiest way to use MOLD is to enable the CMake option WITH_LINKER_MOLD.

Once built you can check for a symbol that should be hidden with nm -D ./blender | grep " T LLVM" compare this with the results of using a different linker such as enabling WITH_LINKER_LLD (make sure to disable mold also).

You can find our map file in blender.map

Desired results

nm -D ./blender | grep " T LLVM" should return nothing.

You could also try to run the application, building with mold should result in a crash during the program initialization.

[LazyDodo]

Sorry about this report, usually when we reach out to other projects we try not to file any "build all of blender" issues, @Blendify got a little trigger happy my apologies.

I extracted a minimal repro case below:

mold_version_issue.tar.gz

as you can see below, when linked with ld, B_func1 and B_func2 are no longer exported, however when linked with mold, both are still there.

root@SRV:/mnt/e/mold_test# mkdir build
root@SRV:/mnt/e/mold_test# cd build
root@SRV:/mnt/e/mold_test/build# cmake ..
-- The C compiler identification is GNU 9.3.0
-- The CXX compiler identification is GNU 9.3.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /mnt/e/mold_test/build
root@SRV:/mnt/e/mold_test/build# make
Scanning dependencies of target libB
[ 16%] Building C object CMakeFiles/libB.dir/b.c.o
[ 33%] Linking C static library liblibB.a
[ 33%] Built target libB
Scanning dependencies of target libA
[ 50%] Building C object CMakeFiles/libA.dir/a.c.o
[ 66%] Linking C static library liblibA.a
[ 66%] Built target libA
Scanning dependencies of target version_test
[ 83%] Building C object CMakeFiles/version_test.dir/vtest.c.o
[100%] Linking C shared library libversion_test.so
[100%] Built target version_test
root@SRV:/mnt/e/mold_test/build# readelf --dyn-syms ./libversion_test.so

Symbol table '.dynsym' contains 9 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_deregisterTMCloneTab
     2: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND puts@GLIBC_2.2.5 (2)
     3: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__
     4: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_registerTMCloneTable
     5: 0000000000000000     0 FUNC    WEAK   DEFAULT  UND __cxa_finalize@GLIBC_2.2.5 (2)
     6: 000000000000118c    23 FUNC    GLOBAL DEFAULT   14 A_func1
     7: 0000000000001159    51 FUNC    GLOBAL DEFAULT   14 vtest
     8: 00000000000011a3    23 FUNC    GLOBAL DEFAULT   14 A_func2
root@SRV:/mnt/e/mold_test/build# cmake -DUSE_MOLD=On .
-- Configuring done
-- Generating done
-- Build files have been written to: /mnt/e/mold_test/build
root@SRV:/mnt/e/mold_test/build# make
[ 16%] Building C object CMakeFiles/libB.dir/b.c.o
[ 33%] Linking C static library liblibB.a
[ 33%] Built target libB
[ 50%] Building C object CMakeFiles/libA.dir/a.c.o
[ 66%] Linking C static library liblibA.a
[ 66%] Built target libA
[ 83%] Building C object CMakeFiles/version_test.dir/vtest.c.o
[100%] Linking C shared library libversion_test.so
[100%] Built target version_test
root@SRV:/mnt/e/mold_test/build# readelf --dyn-syms ./libversion_test.so

Symbol table '.dynsym' contains 11 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__
     2: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_deregisterTMCloneTab
     3: 0000000000000000     0 NOTYPE  WEAK   DEFAULT  UND _ITM_registerTMCloneTable
     4: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND puts@GLIBC_2.2.5 (2)
     5: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND __cxa_finalize@GLIBC_2.2.5 (2)
     6: 0000000000001159    51 FUNC    GLOBAL DEFAULT   17 vtest
     7: 000000000000118c    23 FUNC    GLOBAL DEFAULT   17 A_func1
     8: 00000000000011a3    23 FUNC    GLOBAL DEFAULT   17 A_func2
     9: 00000000000011ba    23 FUNC    GLOBAL DEFAULT   17 B_func1
    10: 00000000000011d1    23 FUNC    GLOBAL DEFAULT   17 B_func2

[rui314]

I'm happy to fix the issue for Blender. Chances are there are many more programs that see the same issue in their builds. Let me take a look.

[Blendify]

Can confirm the issue has been fixed, thanks again :)

[LazyDodo]

Mostly fixed, there's one other side case mold missed, but I'll file a separate bug for that one., since it's quite a different beast than this one.