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Windows extended contexts must be allocated by InitializeContext2 and
may not be aligned. This means we cannot simply store a struct in
our thread snapshot object, but must instead store enough memory
and alias our struct onto this backing memory.
Note that shadow stack pointers are not yet recorded for the initial
exception - this cannot be determined using LocateXStateFeature in
the capturing process and will be added in a future CL by plumbing
through client messages when a crashed process requests a dump.
See crash/32bd2c53a252705c for an example dump with this baked into
chrome, that has passed through breakpad without breaking it. Local
testing shows this creates valid dumps when built into Chrome, but
that the referenced memory limits may need to be increased to allow
for ssp referenced memory to be included.
See "MANAGING STATE USING THE XSAVE FEATURE SET" Chapter 13 in the
Intel SDM[0]. Many of the offsets and sizes of the extended features
are provided by cpu specific values. We can access these in Windows
using the SDK, and transfer these to the saved extended context
which in turn is understandable by windbg.
Further information is available from AMD Ch. 18 "Shadow Stacks"[1].
[0] https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-1-2a-2b-2c-2d-3a-3b-3c-3d-and-4.html.
[1] https://www.amd.com/system/files/TechDocs/24593.pdf
Bug: 1250098
Change-Id: I4b13bcb023e9d5fba257044abfd7e251d66a9329
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/3300992
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
Commit-Queue: Alex Gough <ajgo@chromium.org>