[llvm-dev] ld.lld ignoring --sysroot

[Ivan Medoedov via llvm-dev]

Thanks for the replies.

Rui, with your command I get

ld.lld: error: unknown emulation: elf_x86-64
ld.lld: error: unable to find library -lc
ld.lld: error: cannot open /linuxroot/usr/lib/x86_64-linux-gnu/crtn.o: No
such file or directory


> For your case, you need a linker script located under /linuxroot/, which
INPUT or GROUP an absolute path.

Do you have an example of such linker script? I have no idea how this works.

On Thu, May 14, 2020 at 8:06 AM Fangrui Song <maskray at google.com> wrote:

> On 2020-05-14, Rui Ueyama via llvm-dev wrote:
> >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 x86_64-linux-gnu -c -o hello.o hello.c
> >>
> >> But linking results in an error:
> >>
> >> ld.lld --sysroot=/linuxroot/ -o hello -m elf_x86_64 \
> >>   -dynamic-linker /lib64/ld-linux-x86-64.so.2 \
> >>   /lib/crt1.o \
> >>   /usr/lib/x86_64-linux-gnu/crti.o ../hello.o \
> >>   /usr/lib/x86_64-linux-gnu/libc.so \
> >>   /usr/lib/x86_64-linux-gnu/crtn.o
> >>
> >> ld.lld: error: cannot open /lib/crt1.o: No such file or directory
> >> ld.lld: error: cannot open /usr/lib/x86_64-linux-gnu/crti.o: No such
> file
> >> or directory
> >>
>
> You misunderstand GNU ld's --sysroot rule, which is applicable in these
> two cases:
>
> * when a path begins with "=" or "$SYSROOT"
> * https://www.sourceware.org/binutils/docs/ld/File-Commands.html
>    "In case a sysroot prefix is configured, and the filename starts with
>    the ‘/’ character, and the script being processed was located inside
>    the sysroot prefix, the filename will be looked for in the sysroot
>    prefix."
>
> For your case, you need a linker script located under /linuxroot/, which
> INPUT or GROUP an absolute path.
>
> >--sysroot affects some library search paths, but it doesn't affect paths
> >directly given to the linker. In the above command line, you are directly
> >specifying object file and so file paths without -l, so the linker looks
> at
> >the only given locations. This is an expected behavior.
> >
> >I think, unlike some other linkers, --sysroot option isn't very useful for
> >lld, because lld doesn't have a notion of built-in default search paths.
> >You always have to specify library search paths by -L option to lld. So
> why
> >don't you specify library directories with -L, like this?
> >
> >$ 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/x86_64-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/x86_64-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!
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
>
> >_______________________________________________
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>
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