[all-commits] [llvm/llvm-project] 1a4b9b: [asan] Ensure __asan_register_elf_globals is calle...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1a4b9b6f73391d94f4f96cc964cbf89cfdd59b5b
      https://github.com/llvm/llvm-project/commit/1a4b9b6f73391d94f4f96cc964cbf89cfdd59b5b
  Author: Fangrui Song <i at maskray.me>
  Date:   2023-09-29 (Fri, 29 Sep 2023)

  Changed paths:
    M llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
    M llvm/test/Instrumentation/AddressSanitizer/basic.ll
    M llvm/test/Instrumentation/AddressSanitizer/global_metadata_array.ll

  Log Message:
  -----------
  [asan] Ensure __asan_register_elf_globals is called in COMDAT asan.module_ctor (#67745)

On ELF platforms, when there is no global variable, 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.

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
```