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Re: [PATCH] Fix broken recursion detection when printing static members


On 2017-10-24 06:59, Patrick Frants wrote:
I am so sorry, looks like git send-email removed the first N lines. Here is
the complete changelog:

Fix broken recursion detection when printing static members

Recursion detection for static members was broken. The implementation uses a growing (and shrinking) obstack object to simulate a stack of addresses (CORE_ADDR). Pushing addresses is implemented by calling obstack_grow(),
while popping is implemented by calling obstack_free(). The latter is
problematic because obstack_free() expects a pointer to the base of an
object. When popping elements of the stack however, obstack_free() was
called with the new top, which potentially is not the same as the base of the stack. This is unintended use and the effect is that obstack->next_free
and obstack->object_base members are assigned the value of the new top,
which equals an empty stack. Summary: popping elements would always result
in an empty stack, which breaks the recursion detection.

The fix shrinks the stack using obstack_blank_fast() with a negative value
as described at the bottom of this page:
https://gcc.gnu.org/onlinedocs/libiberty/Extra-Fast-Growing.html
"You can use obstack_blank_fast with a “negative” size argument to make the
current object smaller. Just don’t try to shrink it beyond zero
length—there’s no telling what will happen if you do that. Earlier versions of obstacks allowed you to use obstack_blank to shrink objects. This will
no longer work."

Thanks for the nice description!

Simon


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