llvm/llvm-project

crash when section has `.cfi_startproc` but no `.cfi_endproc`

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#177852 opened on Jan 25, 2026

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crashgood first issuellvm:mc

Description

LLVM crashes on this program

https://godbolt.org/z/9W51vc3bW

module asm ".pushsection .text.foo,\22ax\22, @progbits"
module asm ".type foo, @function"
module asm "foo:"
module asm ".cfi_startproc"
module asm ".popsection"

module asm ".type bar, @function"
module asm "bar:"
module asm ".cfi_startproc"
module asm ".cfi_endproc"

llc: /root/llvm-project/llvm/lib/MC/MCExpr.cpp:223: llvm::MCSymbolRefExpr::MCSymbolRefExpr(const llvm::MCSymbol*, llvm::MCExpr::Spec, const llvm::MCAsmInfo*, llvm::SMLoc): Assertion `Symbol' failed.

This assembly is malformed (but in a way that might come up during development). When the .popsection is removed, we actually get a nice error:

<inline asm>:8:1: error: starting new .cfi frame before finishing the previous one
.cfi_endproc
^
Compiler returned: 1

I think that .popsection should emit an error when the section opened a CFI scope that wasn't yet closed.

Contributor guide

Tech stack
cpp
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
understanding of CFI directivesfamiliarity with LLVM MC layer
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the assembly parsing code, likely in llvm/lib/MC/MCParser/AsmParser.cpp or MCStreamer.cpp, to understand how .cfi startproc and .cfi endproc directives are tracked. The issue suggests that .popsection should emit an error when a CFI scope is left open. Look for where section push/pop operations are handled and add a check for pending CFI frames before allowing a section pop. The existing error message 'starting new .cfi frame before finishing the previous one' indicates the tracking mechanism exists; extend it to .popsection.