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gh-156466: fix cleanup on error after Enter in codegen_enter_scope #156467

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gh-156466: fix cleanup on error after Enter in codegen_enter_scope #156467

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8 changes: 4 additions & 4 deletions Python/codegen.c
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Original file line number Diff line number Diff line change
Expand Up @@ -695,13 +695,13 @@ codegen_enter_scope(compiler *c, identifier name, int scope_type,
* of 0. This is because RETURN_GENERATOR pushes the generator
before returning. */
location loc = LOCATION(lineno, lineno, -1, -1);
ADDOP(c, loc, RETURN_GENERATOR);
ADDOP(c, loc, POP_TOP);
ADDOP_IN_SCOPE(c, loc, RETURN_GENERATOR);
ADDOP_IN_SCOPE(c, loc, POP_TOP);
}

ADDOP_I(c, loc, RESUME, RESUME_AT_FUNC_START);
ADDOP_I_IN_SCOPE(c, loc, RESUME, RESUME_AT_FUNC_START);

@carljm carljm Aug 28, 2026

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I think we should also guard the final _PyCompile_ExitScope(c) in _PyCompile_CodeGen() with if (c->u != NULL), as compiler_mod() does?

If allocating the module's initial RESUME fails, this now exits the only scope and leaves c->u as NULL. _PyCompile_CodeGen() then reaches its unconditional final exit (Python/compile.c:1738), which dereferences c->u and segfaults.

I reproduced this with an allocator hook that fails the initial instruction-buffer allocation during:

import ast
import _testinternalcapi

_testinternalcapi.compiler_codegen(ast.parse("pass"), "<test>", 0)

Main propagates MemoryError, whereas this PR crashes. Normal compile() already handles the cleanup correctly.

if (scope_type == COMPILE_SCOPE_MODULE) {
ADDOP(c, loc, ANNOTATIONS_PLACEHOLDER);
ADDOP_IN_SCOPE(c, loc, ANNOTATIONS_PLACEHOLDER);
}
return SUCCESS;
}
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