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

[Ivan Medoedov via llvm-dev]

Sorry, it's just

ld.lld: error: unknown emulation: elf_x86-64
ld.lld: error: unable to find library -lc

Path to /linuxroot/usr/lib/x86_64-linux-gnu/crtn.o is correct

On Thu, May 14, 2020 at 12:58 PM Ivan Medoedov <ivan.medoedov at gmail.com>
wrote:

> 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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>> >llvm-dev at lists.llvm.org
>> >https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
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