[llvm-bugs] [Bug 34868] New: Add attribute for asserting that memory is valid
llvm-bugs at lists.llvm.org
Sat Oct 7 01:43:12 PDT 2017
Bug ID: 34868
Summary: Add attribute for asserting that memory is valid
OS: Windows NT
Component: Static Analyzer
Assignee: kremenek at apple.com
Reporter: akrzemi1 at gmail.com
CC: llvm-bugs at lists.llvm.org
The following page provides a set of hints for disabling false positives
returned from static-analyzer: http://clang-analyzer.llvm.org/faq.html
Using an `assert` is very elegant; and using `#define`, although not elegant is
a good last resort that makes in possible to disable practically any warning.
Yet, there is a class of false positives that cannot be disabled with an
`assert` and are to specific/focused to qualify for a #define, namely the
problems with memory used after free.
I recently got hit by the following false positive:
It had already been described, and a corresponding bug report filed under
https://bugs.llvm.org/show_bug.cgi?id=28053 15 months ago.
What would help me here is if clang provided an additional attribute, like
`__attribute__((analyzer_memory_valid))`, which I could use to instruct the
analyzer that memory under given address is valid at this point, regardless of
what the analyzer has concluded.
I had a different false positive recently in my job. I cannot make a
self-contained example, because the bug manifested only in big portions of
code, using a number of libraries, and each time I tried to reduce it, the bug
disappeared. But it basically said that the re is a risk memory would not be
freed if some exception was thrown (but the memory in question was guarded by a
std::unique_ptr). What I was missing was another attribute, like
`__attribute__((analyzer_memory_will_be_freed))` wherewith I could overwrite
the conclusion from the static analyzer.
Provide two additional attributes for the static analyzer, where I can add
manual input to the analysis as to when memory is valid, and that it will be
`__attribute__((analyzer_memory_valid))` -- this means that at this point of
execution the memory under the annotated pointer is valid (in particular: not
`__attribute__((analyzer_memory_will_be_freed))` -- this means that the memory
under the annotated address will be freed, even if the analyzer fails to see
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