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Updating docs for poison-in-dtor.
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Authored by nmusgrave on Sep 16 2015, 3:33 PM.

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rGbf8f00586a86: Updating docs for MSan to describe poison-in-dtor.
rC247871: Updating docs for MSan to describe poison-in-dtor.

Summary

Describe the compile and runtime flags to enable MemorySanitizer
detection of use-after-destroy.

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nmusgrave updated this revision to Diff 34934.Sep 16 2015, 3:33 PM

nmusgrave retitled this revision from to Updating docs for poison-in-dtor..

nmusgrave updated this object.

nmusgrave added a reviewer: eugenis.

nmusgrave added a subscriber: llvm-commits.

eugenis added inline comments.Sep 16 2015, 4:06 PM

docs/UsersManual.rst
1068	This is a user-facing manual, avoid using specialized terms like "poisoning". Say that this enabled use-after-destruction detection and that with this the object memory is considered uninitialized after the destructor has run.
1072	Until poison_in_dtor defaults to 1, we should consider this feature experimental. Say so, and make it clear that poison_in_dtor=1 is required for the flag to have any effect.
1074	not "fails", but is reported as a use of uninitialized value

Revise doc description of use-after-dtor.

eugenis added inline comments.Sep 16 2015, 5:08 PM

docs/UsersManual.rst
1070	maybe "the object memory is considered undefined" It is still writable and can be reused with a placement new, or any other way.

Change wording to specify memory no longer readable.

LGTM

This revision is now accepted and ready to land.Sep 16 2015, 5:11 PM

nmusgrave closed this revision.Sep 16 2015, 5:14 PM

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UsersManual.rst

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Diff 34945

docs/UsersManual.rst

Show First 20 Lines • Show All 1,059 Lines • ▼ Show 20 Lines	- ``-fsanitize-memory-track-origins[=level]``: Enables origin tracking in
uninitialized bits came from. Slows down execution by additional		uninitialized bits came from. Slows down execution by additional
1.5x-2x.		1.5x-2x.

Possible values for level are 0 (off), 1, 2 (default). Level 2		Possible values for level are 0 (off), 1, 2 (default). Level 2
adds more sections to MemorySanitizer reports describing the		adds more sections to MemorySanitizer reports describing the
order of memory stores the uninitialized value went		order of memory stores the uninitialized value went
through. This mode may use extra memory in programs that copy		through. This mode may use extra memory in programs that copy
uninitialized memory a lot.		uninitialized memory a lot.
		- ``-fsanitize-memory-use-after-dtor``: Enables use-after-destruction
		eugenisUnsubmitted Done Reply Inline Actions This is a user-facing manual, avoid using specialized terms like "poisoning". Say that this enabled use-after-destruction detection and that with this the object memory is considered uninitialized after the destructor has run. eugenis: This is a user-facing manual, avoid using specialized terms like "poisoning". Say that this…
		detection in MemorySanitizer. After invocation of the destructor,
		the object is considered no longer readable. Facilitates the
		eugenisUnsubmitted Done Reply Inline Actions maybe "the object memory is considered undefined" It is still writable and can be reused with a placement new, or any other way. eugenis: maybe "the object memory is considered undefined" It is still writable and can be reused with…
		detection of use-after-destroy bugs.

		eugenisUnsubmitted Done Reply Inline Actions Until poison_in_dtor defaults to 1, we should consider this feature experimental. Say so, and make it clear that poison_in_dtor=1 is required for the flag to have any effect. eugenis: Until poison_in_dtor defaults to 1, we should consider this feature experimental. Say so, and…
		Setting the MSAN_OPTIONS=poison_in_dtor=1 enables the poisoning of
		memory at runtime. Any subsequent access to the destroyed object
		eugenisUnsubmitted Done Reply Inline Actions not "fails", but is reported as a use of uninitialized value eugenis: not "fails", but is reported as a use of uninitialized value
		fails at runtime. This feature is still experimental, but this
		environment variable must be set to 1 in order for the above flag
		to have any effect.

The ``-fsanitize=`` argument must also be provided when linking, in		The ``-fsanitize=`` argument must also be provided when linking, in
order to link to the appropriate runtime library. When using		order to link to the appropriate runtime library. When using
``-fsanitize=vptr`` (or a group that includes it, such as		``-fsanitize=vptr`` (or a group that includes it, such as
``-fsanitize=undefined``) with a C++ program, the link must be		``-fsanitize=undefined``) with a C++ program, the link must be
performed by ``clang++``, not ``clang``, in order to link against the		performed by ``clang++``, not ``clang``, in order to link against the
C++-specific parts of the runtime library.		C++-specific parts of the runtime library.

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