llvm dev - Jan 2017 - CFI, Safe-Stack, and -fno-sanitize-trap

Hi,

I am using clang++3.9 to build a simple program with both CFI and safe-stack. I
am getting linker errors when combining -fsanitize=safe-stack, -fsanitize=cfi,
and -fno-sanitize-trap=all. Combining safe-stack and CFI without
-fno-sanitize-trap=all works as expected.

It looks like clang is attempting to link in two compiler-rt libraries, one for
ubsan and one for safestack, and this causes multiply defined symbols.

Is this the expected behavior? Can only one sanitizer at a time have trapping
disabled?

The command line to trigger is below.

---
$ clang++-3.9 -flto -fvisibility=default -fsanitize=safe-stack -fsanitize=cfi
-fuse-ld=gold -fno-sanitize-trap=all hello.cpp
... lots of multiply defined symbol errors...
/usr/bin/ld.gold: error:
/usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib/linux/libclang_rt.safestack-x86_64.a(sanitizer_common_nolibc.cc.o):
multiple definition of '__sanitizer::Abort()'
/usr/bin/ld.gold:
/usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib/linux/libclang_rt.ubsan_standalone-x86_64.a(sanitizer_posix_libcdep.cc.o):
previous definition here
/usr/bin/ld.gold: error:
/usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib/linux/libclang_rt.safestack-x86_64.a(sanitizer_common_nolibc.cc.o):
multiple definition of '__sanitizer::SleepForSeconds(int)'
/usr/bin/ld.gold:
/usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib/linux/libclang_rt.ubsan_standalone-x86_64.a(sanitizer_posix_libcdep.cc.o):
previous definition here
clang: error: linker command failed with exit code 1 (use -v to see invocation)
---

hello.cpp:
---
#include <iostream>

int main(int argc, const char* argv[]) {
    std::cout << "Hello, World\n";
    return 0;
}
---

Thanks,
Artem
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Hi Artem,

Thanks for the bug report! It should certainly be possible to use safestack
with CFI in non-trapping mode, or indeed with any other sanitizer. I've
sent https://reviews.llvm.org/D29545 for review which should fix this bug.

Peter

On Tue, Jan 31, 2017 at 11:34 AM, Artem Dinaburg via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> I am using clang++3.9 to build a simple program with both CFI and
> safe-stack. I am getting linker errors when combining
> -fsanitize=safe-stack, -fsanitize=cfi, and -fno-sanitize-trap=all.
> Combining safe-stack and CFI without -fno-sanitize-trap=all works as
> expected.
>
> It looks like clang is attempting to link in two compiler-rt libraries,
> one for ubsan and one for safestack, and this causes multiply defined
> symbols.
>
> Is this the expected behavior? Can only one sanitizer at a time have
> trapping disabled?
>
> The command line to trigger is below.
>
> ---
> $ clang++-3.9 -flto -fvisibility=default -fsanitize=safe-stack
> -fsanitize=cfi -fuse-ld=gold -fno-sanitize-trap=all hello.cpp
> ... lots of multiply defined symbol errors...
> /usr/bin/ld.gold: error: /usr/lib/llvm-3.9/bin/../lib/
> clang/3.9.1/lib/linux/libclang_rt.safestack-x86_64.
> a(sanitizer_common_nolibc.cc.o): multiple definition of
> '__sanitizer::Abort()'
> /usr/bin/ld.gold: /usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib/linux/
> libclang_rt.ubsan_standalone-x86_64.a(sanitizer_posix_libcdep.cc.o):
> previous definition here
> /usr/bin/ld.gold: error: /usr/lib/llvm-3.9/bin/../lib/
> clang/3.9.1/lib/linux/libclang_rt.safestack-x86_64.
> a(sanitizer_common_nolibc.cc.o): multiple definition of
> '__sanitizer::SleepForSeconds(int)'
> /usr/bin/ld.gold: /usr/lib/llvm-3.9/bin/../lib/clang/3.9.1/lib/linux/
> libclang_rt.ubsan_standalone-x86_64.a(sanitizer_posix_libcdep.cc.o):
> previous definition here
> clang: error: linker command failed with exit code 1 (use -v to see
> invocation)
> ---
>
> hello.cpp:
> ---
> #include <iostream>
>
> int main(int argc, const char* argv[]) {
>     std::cout << "Hello, World\n";
>     return 0;
> }
> ---
>
> Thanks,
> Artem
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>

-- 
-- 
Peter
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