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On ELF platforms, when there is no global variable and the unique module ID is non-empty, COMDAT asan.module_ctor is created with no `__asan_register_elf_globals` calls. If this COMDAT is the prevailing copy selected by the linker, the linkage unit will have no `__asan_register_elf_globals` call: the redzone will not be poisoned and ODR violation checker will not work (#67677). This behavior is benign for -fno-sanitize-address-globals-dead-stripping because asan.module_ctor functions that call `__asan_register_globals` (`InstrumentGlobalsWithMetadataArray`) do not use COMDAT. To fix #67677: * Use COMDAT for -fsanitize-address-globals-dead-stripping on ELF platforms. * Call `__asan_register_elf_globals` even if there is no global variable. * If the unique module ID is empty, don't call SetComdatForGlobalMetadata: placing `@.str` in a COMDAT would incorrectly discard internal COMDAT `@.str` in other compile units. Alternatively, when there is no global variable, asan.module_ctor is not COMDAT and does not call `__asan_register_elf_globals`. However, the asan.module_ctor function cannot be eliminated by the linker. Tested the following script. Only ELF -fsanitize-address-globals-dead-stripping has changed behaviors. ``` echo > a.cc # no global variable, empty uniqueModuleId echo 'void f() {}' > b.cc # with global variable, with uniqueModuleId echo 'int g;' > c.cc # with global variable for t in x86_64-linux-gnu arm64-apple-macosx x86_64-windows-msvc; do for gc in -f{,no-}sanitize-address-globals-dead-stripping; do for f in a.cc b.cc c.cc; do echo /tmp/Rel/bin/clang -S --target=$t -fsanitize=address $gc $f -o - /tmp/Rel/bin/clang -S --target=$t -fsanitize=address $gc $f -o - | sed -n '/asan.module_ctor/,/ret/p' done done done ``` --- Identical to commit 16eed8c906875e748c3cb610f3dc4b875f3882aa. 6420d3301cd4f0793adcf11f59e8398db73737d8 is an incorrect revert for genuine purely internal issues.
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