[llvm-bugs] [Bug 39316] New: BPF target: segfault on access to a volatile array in a loop

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39316

            Bug ID: 39316
           Summary: BPF target: segfault on access to a volatile array in
                    a loop
           Product: new-bugs
           Version: 6.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: elazarg at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 21009
  --> https://bugs.llvm.org/attachment.cgi?id=21009&action=edit
zip file with bitcode, disassembly and source C file

Certain combinations of loops and volatile seems to confuse the BPF backend and
in this case cause a segfault. 

As far as I understand, llc should not report any error in this example, even
though the Linux BPF verifier will reject it for having a back edge.

Output:

$ llc-6.0 -march=bpf -filetype=obj bug_segfault.bc
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm3sys15PrintStackTraceERNS_11raw_ostreamE+0x2a)[0x7f17f64e20ea]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm3sys17RunSignalHandlersEv+0x56)[0x7f17f64e0366]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(+0x81c49b)[0x7f17f64e049b]
/lib/x86_64-linux-gnu/libc.so.6(+0x3ef20)[0x7f17f5588f20]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm12SelectionDAG16getGlobalAddressEPKNS_11GlobalValueERKNS_5SDLocENS_3EVTElbh+0x5c)[0x7f17f6ab682c]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZNK4llvm17BPFTargetLowering18LowerGlobalAddressENS_7SDValueERNS_12SelectionDAGE+0x66)[0x7f17f7b64ab6]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(+0xd0a751)[0x7f17f69ce751]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm12SelectionDAG8LegalizeEv+0x328)[0x7f17f69d1e38]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm16SelectionDAGISel17CodeGenAndEmitDAGEv+0x1e8)[0x7f17f6ad9bf8]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm16SelectionDAGISel20SelectAllBasicBlocksERKNS_8FunctionE+0x147c)[0x7f17f6ae33fc]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(+0xe21905)[0x7f17f6ae5905]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm19MachineFunctionPass13runOnFunctionERNS_8FunctionE+0x90)[0x7f17f6786fe0]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm13FPPassManager13runOnFunctionERNS_8FunctionE+0x278)[0x7f17f65bc7f8]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm13FPPassManager11runOnModuleERNS_6ModuleE+0x33)[0x7f17f65bc843]
/usr/lib/llvm-6.0/bin/../lib/libLLVM-6.0.so.1(_ZN4llvm6legacy15PassManagerImpl3runERNS_6ModuleE+0x30f)[0x7f17f65bc08f]
llc-6.0(+0x21861)[0x556bff9dd861]
llc-6.0(main+0x3f5)[0x556bff9d25d5]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7)[0x7f17f556bb97]
llc-6.0(_start+0x2a)[0x556bff9d275a]
Stack dump:
0.      Program arguments: llc-6.0 -march=bpf -filetype=obj bug_segfault.bc 
1.      Running pass 'Function Pass Manager' on module 'bug_segfault.bc'.
2.      Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function
'@manual_memcpy'
Segmentation fault (core dumped)

Details:
LLVM version 6.0.0

Optimized build.
Default target: x86_64-pc-linux-gnu
Host CPU: skylake

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