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

Thu May 14 16:48:16 PDT 2020

I managed to make it work with

ld.lld -L /linuxroot/usr/lib/x86_64-linux-gnu/ \
  --sysroot=/linuxroot/ -v -o hello -m elf_x86_64 \
  -dynamic-linker /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 \
  crt1.o \
  crti.o ../hello.o \
  ./lib/x86_64-linux-gnu/libc.so.6 \
  -lc \
  crtn.o

Thanks for your help

On Thu, May 14, 2020 at 1:00 PM Ivan Medoedov <ivan.medoedov at gmail.com>
wrote:

> 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
>>> >>
>>>
>>> >_______________________________________________
>>> >LLVM Developers mailing list
>>> >llvm-dev at lists.llvm.org
>>> >https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
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