Parser crash on Clang 20.1.3 for BPF code.

[etsal]

STEPS TO REPLICATE

git clone -b clangcrash https://github.com/etsal/scx.git scx;
cd scx/scheds/rust/scx_p2dq;
cargo build;

DESCRIPTION

Over at the sched_ext project we have recently started encountering compiler crashes, seemingly in the [parser] (https://github.com/user-attachments/files/20301509/clangcrash.txt). These crashes do not have an obvious cause, but seem to be triggered by code that uses BPF arenas.

topology-c68477.c.txt
topology-c68477.sh.txt

[etsal]

As a note, the actual source code in topology-c68477.c.txt is at the bottom of the file. Most of the file is declarations/definitions from the vmlinux.h header we include.

[AaronBallman]

         #11 0x00007f07631ef34d clang::Sema::CorrectDelayedTyposInExpr(clang::Expr*, clang::VarDecl*, bool, llvm::function_ref<clang::ActionResult<clang::Expr*, true> (clang::Expr*)>) (/lib64/libclang-cpp.so.20.1+0x11ef34d)

This looks like it's another delayed typo correction issue.

[etsal]

Thank you for looking into this. Yes, as an update: the offending line seems to be https://github.com/etsal/scx/blob/1dd5ea5458f26a8f2342ef5207cac9a0f24321bd/lib/topology.bpf.c#L233 . The variable topo_parent does not exist. Renaming the variable fixes the issue. Whether the crash happens also seems to depend on the name of the nonexistent variable.

[AaronBallman]

Good to know, thank you for the confirmation!

[someone12469]

Reduces with creduce to:

__attribute__((address_space(1))) typedef *a;
topo_print() {
  a b;
  b = topo_parent

Or, if we don't require the crash call stack to contain CorrectDelayedTyposInExpr, to:

__attribute__((address_space(1))) typedef *a;
topo_print() a b = topo_parent

Found this issue by noticing a CorrectDelayedTyposInExpr crash in C++ while reducing a likely-unrelated testcase:

struct a b {
  ::c(a) & d

I don't know if it's worthy of a separate issue. All three crashes happen on master and master with #140571 applied.