Allow CFI with crt-static

[ahomescu]

I am working on enabling CFI on the Trusty OS. After adding "supported-sanitizers": ["cfi"], to a custom copy of aarch64-unknown-trusty I also needed to set "crt-static-default": false. Otherwise I would get an error about sanitizers being incompatible with static linking.

With the two target changes, CFI is working as intended on Trusty.

The check and error were introduced to fix #85459, and the issue specifically mentions Linux. Could the check be relaxed to allow CFI (and maybe other sanitizers) together with crt-static outside of Linux?

[jakos-sec]

From what I can tell the linked PR (#85559) just ensures better error messages and doesn't cause any direct behavior changes for Linux.

The base config of Linux sets crt_static_respected = true does that help in any way?

[ahomescu]

Does the sess.err(...) on line 1518 in https://github.com/rust-lang/rust/pull/85559/changes not stop compilation?

[jakos-sec]

Yes, but you said it's specific about Linux, right? I only see Linux mentioned in the comment but the code is not checking for Linux specifically.

[ahomescu]

I only see Linux mentioned in the comment but the code is not checking for Linux specifically.

Yes, what I am asking for is to check for Linux specifically. Alternatively, it could be "Linux + other OSes that use glibc", or any other option that excludes non-glibc OSes (like Trusty which is what I'm working on). The original check (non-Windows) was too broad.

The original issue at #85459 was only tested on Linux afaict.

[jakos-sec]

I've talked to @ahomescu a little bit offline and I think the issue is primarily that none of the sanitizers are allowed with crt-static right now. While that is correct to not allow with e.g. AddressSanitizer:

$ LANG=C clang -O1 -g -fsanitize=address /tmp/test.c -static
/usr/bin/ld: /usr/lib/llvm-19/lib/clang/19/lib/linux/libclang_rt.asan-x86_64.a(asan_interceptors.cpp.o): in function `InitializeCommonInterceptors()':
(.text._ZL28InitializeCommonInterceptorsv+0x6339): warning: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/bin/ld: /usr/lib/llvm-19/lib/clang/19/lib/linux/libclang_rt.asan-x86_64.a(asan_rtl.cpp.o): in function `__asan::AsanInitInternal()':
(.text._ZN6__asanL16AsanInitInternalEv+0x52): undefined reference to `_DYNAMIC'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I think this should not include CFI which succeeds with -static with clang:

$ LANG=C clang -O1 -g -fsanitize=cfi -flto -fvisibility=hidden /tmp/test.c -static

So it sounds like this issue should be turned around to allow sanitizers (CFI (which technically is not a sanitizer anyways)) with crt-static and only disallow sanitizers with interceptors from usage with crt-static.

[ahomescu]

Thanks @jakos-sec, I updated the issue title.