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bitcode #5

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alexcohn opened this issue Dec 19, 2021 · 0 comments
Open

bitcode #5

alexcohn opened this issue Dec 19, 2021 · 0 comments

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@alexcohn
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alexcohn commented Dec 19, 2021 •
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Apple requires bitcode for tvOS builds, and strongly encourages bitcode for iOS builds. Also, the compiler has recently added a check in clang/lib/Driver/ToolChains/Clang.cpp, which does not allow -mllvm in CFLAGS when -fembed-bitcode is present.

This didn't happen before, on llvm-9.0.1 (but that was not compatible with the modern Xcode).

I tried to simply remove the error check for mllvm from Clang.cpp, but this resulted in lots of suspicious warnings while compiling and my iOS code, I tried to simply hardcode -mllvm -bcf -mllvm -sub -mllvm -fla -mllvm -sobf in the compiler. Now, build passes smoothly.

Is there a better way to work around this problem? Also, I am not sure (have not tried) that the bitcode that is produced after my 'fix' is valid.
hudjefa pushed a commit to hudjefa/obfuscator-llvm that referenced this issue Feb 14, 2022
@yonghong-song @tstellar
BPF: Fix a bug in peephole TRUNC elimination optimization
6564e0c 
Andrei Matei reported a llvm11 core dump for his bpf program
   https://bugs.llvm.org/show_bug.cgi?id=48578
The core dump happens in LiveVariables analysis phase.
  heroims#4 0x00007fce54356bb0 __restore_rt
  heroims#5 0x00007fce4d51785e llvm::LiveVariables::HandleVirtRegUse(unsigned int,
      llvm::MachineBasicBlock*, llvm::MachineInstr&)
  heroims#6 0x00007fce4d519abe llvm::LiveVariables::runOnInstr(llvm::MachineInstr&,
      llvm::SmallVectorImpl<unsigned int>&)
  heroims#7 0x00007fce4d519ec6 llvm::LiveVariables::runOnBlock(llvm::MachineBasicBlock*, unsigned int)
  heroims#8 0x00007fce4d51a4bf llvm::LiveVariables::runOnMachineFunction(llvm::MachineFunction&)
The bug can be reproduced with llvm12 and latest trunk as well.

Futher analysis shows that there is a bug in BPF peephole
TRUNC elimination optimization, which tries to remove
unnecessary TRUNC operations (a <<= 32; a >>= 32).
Specifically, the compiler did wrong transformation for the
following patterns:
   %1 = LDW ...
   %2 = SLL_ri %1, 32
   %3 = SRL_ri %2, 32
   ... %3 ...
   %4 = SRA_ri %2, 32
   ... %4 ...

The current transformation did not check how many uses of %2
and did transformation like
   %1 = LDW ...
   ... %1 ...
   %4 = SRL_ri %2, 32
   ... %4 ...
and pseudo register %2 is used by not defined and
caused LiveVariables analysis core dump.

To fix the issue, when traversing back from SRL_ri to SLL_ri,
check to ensure SLL_ri has only one use. Otherwise, don't
do transformation.

Differential Revision: https://reviews.llvm.org/D97792

(cherry picked from commit 51cdb780db3b9b46c783efcec672c4da272e9992)
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