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The current implementation of -fsanitize=function places two words (the prolog signature and the RTTI proxy) at the function entry, which makes the feature incompatible with Intel Indirect Branch Tracking (IBT) that needs an ENDBR instruction at the function entry. To allow the combination, move the two words before the function entry, similar to -fsanitize=kcfi. Armv8.5 Branch Target Identification (BTI) has a similar requirement. Note: for IBT and BTI, whether a function gets a marker instruction at the entry generally cannot be assumed (it can be disabled by a function attribute or stronger LTO optimizations). It is extremely unlikely for two words preceding a function entry to be inaccessible. One way to achieve this is by ensuring that a function is aligned at a page boundary and making the preceding page unmapped or unreadable. This is not reasonable for application or library code. (Think: the first text section has crt* code not instrumented by -fsanitize=function.) We use 0xc105cafe for all targets. .long 0xc105cafe disassembles to invalid instructions on all architectures I have tested, except Power where it is `lfs 8, -13570(5)` (Load Floating-Point with a weird offset, unlikely to be used in real code). --- For the removed function in AsmPrinter.cpp, remove an assert: `mdconst::extract` already asserts non-nullness. For compiler-rt/test/ubsan/TestCases/TypeCheck/Function/function.cpp, when the function doesn't have prolog/epilog (-O1 and above), after moving the two words, the address of the function equals the address of ret instruction, so symbolizing the function will additionally get a non-zero column number. Adjust the test to allow an optional column number. ``` .long 3238382334 .long .L__llvm_rtti_proxy-_Z1fv _Z1fv: // symbolizing here retrieves the line table entry from the second .loc .file 0 ... .loc 0 1 0 .cfi_startproc .loc 0 2 1 prologue_end retq ``` Reviewed By: peter.smith Differential Revision: https://reviews.llvm.org/D148665
Compiler-RT ================================ This directory and its subdirectories contain source code for the compiler support routines. Compiler-RT is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. ================================