x86 Linux build fails

[t-mustafin]

x86 Linux build fails with message:

  /home/tmustafin/dotnet/runtime/src/coreclr/vm/i386/jithelp.S:314:21: error: cannot use more than one symbol in memory operand
      add eax, offset _GLOBAL_OFFSET_TABLE_+1
                      ^
  vm/wks/CMakeFiles/cee_wks_core.dir/build.make:3330: recipe for target 'vm/wks/CMakeFiles/cee_wks_core.dir/__/i386/jithelp.S.o' failed

Problem occures on

runtime/src/coreclr/vm/i386/jithelp.S

Line 395 in 738b09b

add eax, offset _GLOBAL_OFFSET_TABLE_+1 // (2b - 1b)

.
Build command:

sudo ./eng/common/cross/build-rootfs.sh x86 bionic
ROOTFS_DIR=`pwd`/.tools/rootfs/x86 ./build.sh --cross --clang9 --arch x86 --configuration Release --subset clr.runtime+clr.corelib+clr.iltools+clr.dactools+clr.jit /p:EnableSourceLink=false

cc @janvorli @jkotas @alpencolt @gbalykov

[janvorli]

I've just found that it is a clang issue. The build works fine with clang 10, but not with clang 9 for some reason. @t-mustafin would using clang-10 be an option for you? The clang 9 seems to be somehow confused by the instruction. Even with just add eax, offset _GLOBAL_OFFSET_TABLE_, it complains the same way.

[janvorli]

It seems to be a known issue in clang, apparently fixed in clang >=10:
https://bugs.llvm.org/show_bug.cgi?id=32530

[alpencolt]

@janvorli we use old clang-5 for production builds. Thank you for information, we'll check whether this bug exists on other clang versions.

[janvorli]

I have a workaround that works on the older clangs as well, just verifying that it generates the expected code.

[janvorli]

It seems to generate proper code, the diff is:

diff --git a/src/coreclr/vm/i386/jithelp.S b/src/coreclr/vm/i386/jithelp.S
index dc56da1d177..4f227c9cf60 100644
--- a/src/coreclr/vm/i386/jithelp.S
+++ b/src/coreclr/vm/i386/jithelp.S
@@ -392,7 +392,9 @@ LEAF_ENTRY JIT_WriteBarrier_Callable, _TEXT
 1:
     pop     eax
 2:
-    add     eax, offset _GLOBAL_OFFSET_TABLE_+1 // (2b - 1b)
+.att_syntax
+    addl     $_GLOBAL_OFFSET_TABLE_+(2b-1b), %eax
+.intel_syntax noprefix
     mov     eax, dword ptr [eax + C_FUNC(JIT_WriteBarrierEAX_Loc)@GOT]
     xchg    eax, dword ptr [esp]
     ret

[t-mustafin]

@janvorli Thanks, it works for me with clang9 and clang5.

[alpencolt]

@janvorli btw as I see clang11 is last supported version. Are there plans for adding clang12 support?

[janvorli]

@alpencolt yes, I'd like to support the latest clang releases. I haven't monitored the llvm releases recently, so I've missed the fact that there is a version 12 already. Have you tried it and found issues with it?

[alpencolt]

It seems it was released in April. We haven't tried it yet but want to update our toolchain and I check which version fits more.
If you're ok with using latest one we can check clang12 on ARM close to autumn.

[janvorli]

Usually moving to a new version just works. In some cases, it caused build breaks in the past that we needed to fix.