[llvm-dev] ld.lld ignoring --sysroot (original) (raw)

Rui Ueyama via llvm-dev llvm-dev at lists.llvm.org
Wed May 13 20:22:36 PDT 2020

On Thu, May 14, 2020 at 11:04 AM Ivan Medoedov via llvm-dev < llvm-dev at lists.llvm.org> wrote:

Hello,

I'm trying to compile a Linux hello world executable on macOS. The first step is simple: clang -c -target x8664-linux-gnu -c -o hello.o hello.c But linking results in an error: _ld.lld --sysroot=/linuxroot/ -o hello -m elfx8664 _ _-dynamic-linker /lib64/ld-linux-x86-64.so.2 _ _/lib/crt1.o _ _/usr/lib/x8664-linux-gnu/crti.o ../hello.o _ _/usr/lib/x8664-linux-gnu/libc.so _ /usr/lib/x8664-linux-gnu/crtn.o ld.lld: error: cannot open /lib/crt1.o: No such file or directory ld.lld: error: cannot open /usr/lib/x8664-linux-gnu/crti.o: No such file or directory

--sysroot affects some library search paths, but it doesn't affect paths directly given to the linker. In the above command line, you are directly specifying object file and so file paths without -l, so the linker looks at the only given locations. This is an expected behavior.

I think, unlike some other linkers, --sysroot option isn't very useful for lld, because lld doesn't have a notion of built-in default search paths. You always have to specify library search paths by -L option to lld. So why don't you specify library directories with -L, like this?

$ ld.lld -o hello -m elf_x86-64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -L /linuxroot/usr/lib -lc /linuxroot/usr/lib/x86_64-linux-gnu/crtn.o

/linuxroot/ contains all the necessary files copied from a Linux machine: /linuxroot/lib/crt1.o, /linuxroot/usr/lib/x8664-linux-gnu/crti.o, etc

It works if I use a full path for each file (-dynamic-linker /linuxroot/lib64/ld-linux-x86-64.so.2 ...), but the resulting binary doesn't work on Linux, because it's dynamically linked to /linuxroot/... which is missing on the Linux box. file hi hi: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /linuxroot/lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, not stripped The only way I can make it work is to have actual /usr/lib/x8664-linux-gnu/crti.o etc on my macOS box, which --sysroot is supposed to help avoid. I'm sure I'm missing something simple here. I've been following the docs, but couldn't figure it out on my own. Thanks!

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