[llvm-bugs] [Bug 49835] New: clang asan cross-compile ignoring --sysroot for linker use of --whole-archive

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49835

            Bug ID: 49835
           Summary: clang asan cross-compile ignoring --sysroot for linker
                    use of --whole-archive
           Product: clang
           Version: 7.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C
          Assignee: unassignedclangbugs at nondot.org
          Reporter: cross.jesse.james at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

I cross compile with debian x86_64, and target both aarch64 and armv6l by using
`--sysroot` to point to a complete filesystem (I.E `/cache/arm64` or
`/cache/armel`) for the target architectures. I use `qemu-debootstrap` to
create `/cache/arm64` and `/cache/armel` debian systems, include the necessary
*-dev packages on those systems, and then include those libraries for the
compiler by simply declaring the entire cached system the sysroot
(`--sysroot=/cache/arm64`). This works cleanly for `gcc-8`, but I'm having a
problem cross-compiling with `clang-7` using address-sanitizer.

For example, with aarch64 the linker complains:
```
/usr/bin/aarch64-linux-gnu-ld: cannot find
/usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.asan-aarch64.a: No such
file or directory
```
`libclang_rt.asan-aarch64.a` comes from libclang-common-7-dev:
```
dpkg -S /usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.asan-aarch64.a
libclang-common-7-dev:
/usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.asan-aarch64.a
```
This package and file is installed on the arm64 system. Using `clang -v` I can
see the linker is trying to use `--whole-archive
/usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.asan-aarch64.a` but I
need it to use `--whole-archive
/cache/arm64/usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.asan-aarch64.a`.
The `--sysroot` option is changing all my `-L` options in the linker, but not
this `--whole-archive` option.

I can manually change the linker command to complete compilation. However, I
have further problems.

It seems not to use `/cache/arm64/lib/aarch64-linux-gnu/`, but instead uses
`/lib/aarch64-linux-gnu/` on the host system. If I `rsync` all the
`/cache/arm64/lib/aarch64-linux-gnu/` files to `/lib/aarch64-linux-gnu/` on the
host, and also manually change the linker command, then it "succeeds", except
the binary still fails to run when I `chroot` into the target system:

```
# chroot /cache/arm64 /bin/bash
# ./binary
==13339==Sanitizer CHECK failed:
/build/llvm-toolchain-7-whi4O5/llvm-toolchain-7-7.0.1/projects/compiler-rt/lib/sanitizer_common/sanitizer_procmaps_common.cc:83
((data_.proc_self_maps.mmaped_size)) > ((0)) (0, 0)
````

My motivation for this `--sysroot` approach is merely that it's simple. It
avoids having to `dpkg --add-architecture arm64` and load the libraries onto
the host. Further, in the case of `libclang_rt.asan-aarch64.a` in
libclang-common-7-dev, I couldn't load `libclang-common-7-dev:arm64` if I
wanted to; It conflicts with the `clang` package:

```
apt install libclang-common-7-dev:arm64
Reading package lists... Done
Building dependency tree... Done
The following additional packages will be installed:
  gcc-8-base:arm64 libbsd0:arm64 libbsd0 libc6:arm64 libedit2:arm64
libffi6:arm64 libgcc1:arm64
  libidn2-0:arm64 libllvm7:arm64 libstdc++6:arm64 libtinfo6:arm64
libunistring2:arm64 zlib1g:arm64
Suggested packages:
  glibc-doc:arm64 locales:arm64
The following packages will be REMOVED:
  clang-7 libclang-common-7-dev
The following NEW packages will be installed:
  gcc-8-base:arm64 libbsd0:arm64 libc6:arm64 libclang-common-7-dev:arm64
libedit2:arm64 libffi6:arm64
  libgcc1:arm64 libidn2-0:arm64 libllvm7:arm64 libstdc++6:arm64 libtinfo6:arm64
libunistring2:arm64
  zlib1g:arm64
```
My `clang-7` options: `-v -fPIC -O1  -target aarch64-linux-gnu
--sysroot=/cache/arm64 -fsanitize=address -fno-omit-frame-pointer
-fno-optimize-sibling-calls'`
Also of note: I compile source to assembly, assembly to object, then object to
binary. I perform these steps to retain the intermediate files mostly out of
curiosity. When I do this NOT as a cross-compilation, I have no issues. So, I
shouldn't think it matters, but I'll mention it just in case.

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