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vm.c: refresh regs before storing the OP_GETIDX0 Hash result #7023

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Merged
matz merged 1 commit into from
Aug 9, 2026
Merged

vm.c: refresh regs before storing the OP_GETIDX0 Hash result #7023

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9 changes: 8 additions & 1 deletion src/vm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2124,7 +2124,14 @@ vm_op_getidx0(mrb_state *mrb, uint32_t a, uint16_t b, mrb_sym *midp)
}
else if (tt == MRB_TT_HASH) {
if (mrb_obj_ptr(recv)->c != mrb->hash_class) goto getidx0_fallback;
regs[a] = mrb_hash_get(mrb, recv, mrb_fixnum_value(0));
{
/* same as the Hash branch of vm_op_getidx(): mrb_hash_get() can run a
default proc and move the stack, so take the result first and store
it through the refreshed `regs` */
mrb_value val = mrb_hash_get(mrb, recv, mrb_fixnum_value(0));
ci = mrb->c->ci;
regs[a] = val;
}
return VM_NEXT;
}
getidx0_fallback:
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15 changes: 15 additions & 0 deletions test/t/hash.rb
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Expand Up @@ -996,3 +996,18 @@ def h.default(k); self[k] = 1; end
y = 2
assert_equal({x:1, y:2}, {x:, y:})
end

assert('Hash#[] with a default proc that grows the VM stack') do
# The default proc re-enters the VM, and enough frames of it reallocate the
# stack. `OP_GETIDX0` and `OP_GETIDX` answer from C, so each has to store its
# result through the refreshed registers rather than the ones it came in
# with. The corruption is silent without a sanitizer, so this only fails
# reliably under `build_config/clang-asan.rb`.
def self.deep(n)
return 0 if n == 0
deep(n - 1)
end
h = Hash.new { |_, _| deep(50); :from_proc }
assert_equal :from_proc, h[0]
assert_equal :from_proc, h[1]
end
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