This revision was automatically updated to reflect the committed changes. Closed by commit rL324163: [hwasan] Add a paragraph on stack instrumentation. (authored by eugenis, committed by ). Herald added a subscriber: llvm-commits.
Changed prior to commit: https://reviews.llvm.org/D42874?vs=132708&id=132711#toc Repository: rL LLVM https://reviews.llvm.org/D42874 Files: cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst Index: cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst =================================================================== --- cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst +++ cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst @@ -77,11 +77,18 @@ Stack ----- -Special compiler instrumentation is required to align the local variables -by N, tag the memory and the pointers. +Stack frames are instrumented by aligning all non-promotable allocas +by `N` and tagging stack memory in function prologue and epilogue. + +Tags for different allocas in one function are **not** generated +independently; doing that in a function with `M` allocas would require +maintaining `M` live stack pointers, significantly increasing register +pressure. Instead we generate a single base tag value in the prologue, +and build the tag for alloca number `M` as `ReTag(BaseTag, M)`, where +ReTag can be as simple as exclusive-or with constant `M`. + Stack instrumentation is expected to be a major source of overhead, but could be optional. -TODO: details. Globals -------
Index: cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst =================================================================== --- cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst +++ cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst @@ -77,11 +77,18 @@ Stack ----- -Special compiler instrumentation is required to align the local variables -by N, tag the memory and the pointers. +Stack frames are instrumented by aligning all non-promotable allocas +by `N` and tagging stack memory in function prologue and epilogue. + +Tags for different allocas in one function are **not** generated +independently; doing that in a function with `M` allocas would require +maintaining `M` live stack pointers, significantly increasing register +pressure. Instead we generate a single base tag value in the prologue, +and build the tag for alloca number `M` as `ReTag(BaseTag, M)`, where +ReTag can be as simple as exclusive-or with constant `M`. + Stack instrumentation is expected to be a major source of overhead, but could be optional. -TODO: details. Globals -------
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