Poison VM stack#19334
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dstogov
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Aug 5, 2025
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I can't review this carefully.
The idea looks interesting.
@iluuu1994 @nielsdos please take a look
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+1 on the idea. Can you check why CI reports a (likely) non-noise increase in I-count on Valgrind for e.g. Symfony? Intuitively this shouldn't be the case but somehow it is. |
iluuu1994
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Aug 14, 2025
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| if (UNEXPECTED(used_stack > (size_t)(((char*)EG(vm_stack_end)) - (char*)call))) { | ||
| call = (zend_execute_data*)zend_vm_stack_extend(used_stack); | ||
| ZEND_UNPOISON_MEMORY_REGION(call, used_stack); |
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Oh, my only comment didn't go through. ^^ I was wondering if it may make sense to move this to zend_vm_init_call_frame(), which would avoid a chunk of the ZEND_UNPOISON_MEMORY_REGION() calls.
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Use the ASAN/MSAN interfaces to poison new VM stack pages and poped frames. This is useful because without this instrumentation, ASAN considers memory regions past the current frame as addressable (since we allocate one page at a time), and MSAN considers them initialized if they have been used by other function calls before.
I extracted this from the partials implementation, for which it has been useful to spot issues. This was before #18858 was published, but I still took a little bit of inspiration from it while extracting this PR.