[PATCH] riscv: fix vdso build with lld

[PATCH] riscv: fix vdso build with lld

[Ilie Halip]

When building with the LLVM linker this error occurrs:
    LD      arch/riscv/kernel/vdso/vdso-syms.o
  ld.lld: error: no input files

This happens because the lld treats -R as an alias to -rpath, as opposed
to ld where -R means --just-symbols.

Use the long option name for compatibility between the two.

Link: https://github.com/ClangBuiltLinux/linux/issues/805
Reported-by: Dmitry Golovin <dima@golovin.in>
Signed-off-by: Ilie Halip <ilie.halip@gmail.com>
---
 arch/riscv/kernel/vdso/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 33b16f4212f7..19f7b9ea10ab 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -41,7 +41,8 @@ SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \
 $(obj)/vdso-dummy.o: $(src)/vdso.lds $(obj)/rt_sigreturn.o FORCE
 	$(call if_changed,vdsold)
 
-LDFLAGS_vdso-syms.o := -r -R
+# lld aliases -R to -rpath; use the longer option name
+LDFLAGS_vdso-syms.o := -r --just-symbols
 $(obj)/vdso-syms.o: $(obj)/vdso-dummy.o FORCE
 	$(call if_changed,ld)
 
-- 
2.17.1

Re: [PATCH] riscv: fix vdso build with lld

[Nick Desaulniers]

+ Jordan, Fangrui

On Thu, Apr 2, 2020 at 1:56 AM Ilie Halip <ilie.halip@gmail.com> wrote:
>
> When building with the LLVM linker this error occurrs:
>     LD      arch/riscv/kernel/vdso/vdso-syms.o
>   ld.lld: error: no input files
>
> This happens because the lld treats -R as an alias to -rpath, as opposed
> to ld where -R means --just-symbols.
>
> Use the long option name for compatibility between the two.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/805
> Reported-by: Dmitry Golovin <dima@golovin.in>
> Signed-off-by: Ilie Halip <ilie.halip@gmail.com>
> ---
>  arch/riscv/kernel/vdso/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> index 33b16f4212f7..19f7b9ea10ab 100644
> --- a/arch/riscv/kernel/vdso/Makefile
> +++ b/arch/riscv/kernel/vdso/Makefile
> @@ -41,7 +41,8 @@ SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \
>  $(obj)/vdso-dummy.o: $(src)/vdso.lds $(obj)/rt_sigreturn.o FORCE
>         $(call if_changed,vdsold)
>
> -LDFLAGS_vdso-syms.o := -r -R
> +# lld aliases -R to -rpath; use the longer option name

Thanks for the patch.  Maybe the comment can be dropped? It doesn't
make sense if there's no -R in the source file you're touching.  If
someone cares about why `--just-symbols` is spelled out, that's what
`git log` or vim fugitive is for.  Maybe the maintainer would be kind
enough to just drop that line for you when merging?

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Jordan, Fangrui, thoughts on this? Sounds like something other users
of LLD might run into porting their codebase to LLVM's linker.

$ ld.lld --help | grep \\-R
  -R <value>              Alias for --rpath
$ ld.bfd --help | grep \\-R
  -R FILE, --just-symbols FILE

> +LDFLAGS_vdso-syms.o := -r --just-symbols
>  $(obj)/vdso-syms.o: $(obj)/vdso-dummy.o FORCE
>         $(call if_changed,ld)
>
> --
> 2.17.1
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] riscv: fix vdso build with lld

[Fangrui Song]

The comment of `With ld -R we can then ...` should be fixed as well.

On 2020-04-02, Nick Desaulniers wrote:
>+ Jordan, Fangrui
>
>On Thu, Apr 2, 2020 at 1:56 AM Ilie Halip <ilie.halip@gmail.com> wrote:
>>
>> When building with the LLVM linker this error occurrs:
>>     LD      arch/riscv/kernel/vdso/vdso-syms.o
>>   ld.lld: error: no input files
>>
>> This happens because the lld treats -R as an alias to -rpath, as opposed
>> to ld where -R means --just-symbols.
>>
>> Use the long option name for compatibility between the two.
>>
>> Link: https://github.com/ClangBuiltLinux/linux/issues/805
>> Reported-by: Dmitry Golovin <dima@golovin.in>
>> Signed-off-by: Ilie Halip <ilie.halip@gmail.com>
>> ---
>>  arch/riscv/kernel/vdso/Makefile | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
>> index 33b16f4212f7..19f7b9ea10ab 100644
>> --- a/arch/riscv/kernel/vdso/Makefile
>> +++ b/arch/riscv/kernel/vdso/Makefile
>> @@ -41,7 +41,8 @@ SYSCFLAGS_vdso.so.dbg = -shared -s -Wl,-soname=linux-vdso.so.1 \
>>  $(obj)/vdso-dummy.o: $(src)/vdso.lds $(obj)/rt_sigreturn.o FORCE
>>         $(call if_changed,vdsold)
>>
>> -LDFLAGS_vdso-syms.o := -r -R
>> +# lld aliases -R to -rpath; use the longer option name
>
>Thanks for the patch.  Maybe the comment can be dropped? It doesn't
>make sense if there's no -R in the source file you're touching.  If
>someone cares about why `--just-symbols` is spelled out, that's what
>`git log` or vim fugitive is for.  Maybe the maintainer would be kind
>enough to just drop that line for you when merging?
>
>Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
>Jordan, Fangrui, thoughts on this? Sounds like something other users
>of LLD might run into porting their codebase to LLVM's linker.

Independently, I noticed this ~2 days ago.
https://reviews.llvm.org/D76885#1952860

GNU ld parses options with getopt_long and -j is recognized as
--just-symbols ('R') because there is no other long options prefixed with -j.

Now, the following comment applies. Basically, --just-symbols/-R is an
overloaded option. It can be used as an -rpath if the argument is a directory.
The best practice is to use either -rpath or --just-symbols, never -R.

// binutils-gdb/ld/lexsup.c
	case 'R':
	  /* The GNU linker traditionally uses -R to mean to include
	     only the symbols from a file.  The Solaris linker uses -R
	     to set the path used by the runtime linker to find
	     libraries.  This is the GNU linker -rpath argument.  We
	     try to support both simultaneously by checking the file
	     named.  If it is a directory, rather than a regular file,
	     we assume -rpath was meant.  */
	  {
	    struct stat s;

	    if (stat (optarg, &s) >= 0
		&& ! S_ISDIR (s.st_mode))
	      {
		lang_add_input_file (optarg,
				     lang_input_file_is_symbols_only_enum,
				     NULL);
		break;
	      }
	  }




>$ ld.lld --help | grep \\-R
>  -R <value>              Alias for --rpath
>$ ld.bfd --help | grep \\-R
>  -R FILE, --just-symbols FILE
>
>> +LDFLAGS_vdso-syms.o := -r --just-symbols
>>  $(obj)/vdso-syms.o: $(obj)/vdso-dummy.o FORCE
>>         $(call if_changed,ld)
>>
>> --
>> 2.17.1
>>
>
>
>-- 
>Thanks,
>~Nick Desaulniers