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From a code size perspective it turns out to be better to use a callee-saved register to pass the shadow base. For non-leaf functions it avoids the need to reload the shadow base into x9 after each function call, at the cost of an additional stack slot to save the caller's x20. But with x9 there is also a stack size cost, either as a result of copying x9 to a callee-saved register across calls or by spilling it to stack, so for the non-leaf functions the change to stack usage is largely neutral. It is also code size (and stack size) neutral for many leaf functions. Although they now need to save/restore x20 this can typically be combined via LDP/STP into the x30 save/restore. In the case where the function needs callee-saved registers or stack spills we end up needing, on average, 8 more bytes of stack and 1 more instruction but given the improvements to other functions this seems like the right tradeoff. Unfortunately we cannot change the register for the v1 (non short granules) check because the runtime assumes that the shadow base register is stored in x9, so the v1 check still uses x9. Aside from that there is no change to the ABI because the choice of shadow base register is a contract between the caller and the outlined check function, both of which are compiler generated. We do need to rename the v2 check functions though because the functions are deduplicated based on their names, not on their contents, and we need to make sure that when object files from old and new compilers are linked together we don't end up with a function that uses x9 calling an outlined check that uses x20 or vice versa. With this change code size of /system/lib64/*.so in an Android build with HWASan goes from 200066976 bytes to 194085912 bytes, or a 3% decrease. Differential Revision: https://reviews.llvm.org/D90422 |
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| .. | ||
| analyzer | ||
| CommandGuide | ||
| tools | ||
| AddressSanitizer.rst | ||
| APINotes.rst | ||
| AutomaticReferenceCounting.rst | ||
| Block-ABI-Apple.rst | ||
| Block-ABI-Apple.txt | ||
| BlockLanguageSpec.rst | ||
| ClangCheck.rst | ||
| ClangCommandLineReference.rst | ||
| ClangFormat.rst | ||
| ClangFormatStyleOptions.rst | ||
| ClangFormattedStatus.rst | ||
| ClangPlugins.rst | ||
| ClangStaticAnalyzer.rst | ||
| ClangTools.rst | ||
| CMakeLists.txt | ||
| conf.py | ||
| ConstantInterpreter.rst | ||
| ControlFlowIntegrity.rst | ||
| ControlFlowIntegrityDesign.rst | ||
| CrossCompilation.rst | ||
| DataFlowSanitizer.rst | ||
| DataFlowSanitizerDesign.rst | ||
| DiagnosticsReference.rst | ||
| doxygen-mainpage.dox | ||
| doxygen.cfg.in | ||
| DriverArchitecture.png | ||
| DriverInternals.rst | ||
| ExternalClangExamples.rst | ||
| FAQ.rst | ||
| HardwareAssistedAddressSanitizerDesign.rst | ||
| HowToSetupToolingForLLVM.rst | ||
| index.rst | ||
| InternalsManual.rst | ||
| IntroductionToTheClangAST.rst | ||
| ItaniumMangleAbiTags.rst | ||
| JSONCompilationDatabase.rst | ||
| LanguageExtensions.rst | ||
| LeakSanitizer.rst | ||
| LibASTImporter.rst | ||
| LibASTMatchers.rst | ||
| LibASTMatchersReference.html | ||
| LibASTMatchersTutorial.rst | ||
| LibFormat.rst | ||
| LibTooling.rst | ||
| LTOVisibility.rst | ||
| make.bat | ||
| Makefile.sphinx | ||
| MatrixTypes.rst | ||
| MemorySanitizer.rst | ||
| Modules.rst | ||
| MSVCCompatibility.rst | ||
| ObjectiveCLiterals.rst | ||
| OpenCLSupport.rst | ||
| OpenMPSupport.rst | ||
| PCHInternals.rst | ||
| PCHLayout.graffle | ||
| PCHLayout.png | ||
| RAVFrontendAction.rst | ||
| README.txt | ||
| RefactoringEngine.rst | ||
| ReleaseNotes.rst | ||
| SafeStack.rst | ||
| SanitizerCoverage.rst | ||
| SanitizerSpecialCaseList.rst | ||
| SanitizerStats.rst | ||
| ShadowCallStack.rst | ||
| SourceBasedCodeCoverage.rst | ||
| ThinLTO.rst | ||
| ThreadSafetyAnalysis.rst | ||
| ThreadSanitizer.rst | ||
| Toolchain.rst | ||
| Tooling.rst | ||
| UndefinedBehaviorSanitizer.rst | ||
| UsersManual.rst | ||
See llvm/docs/README.txt