[ELF] - -rpath-link "implemented"

[grimar]

Summary

I think we can just ingnore the "-rpath-link" option. And that can be considered as expected implementation.
My arguments for that below.

Consider we have following sources:

shared2.cpp:

int B() {
 return 0;
}

shared.cpp:

int B();
int A() { 
 return B();
}

main.cpp:

int A();
int main() {
 return A();
}

1. If I link this using bfd (from path /home/umb/tests/59rpath), I get an error:

/home/umb/LLVM/build/bin/clang -shared -fuse-ld=bfd -fPIC shared2.cpp -o shared2.so
/home/umb/LLVM/build/bin/clang -shared -fuse-ld=bfd -fPIC shared.cpp shared2.so -o shared.so
/home/umb/LLVM/build/bin/clang -fuse-ld=bfd main.cpp shared.so -o test

++ /home/umb/LLVM/build/bin/clang -fuse-ld=bfd main.cpp shared.so -o test
/usr/local/bin/ld.bfd: warning: ./shared/shared2.so, needed by shared.so, not found (try using -rpath or -rpath-link)
shared.so: undefined reference to `B()'
clang-3.9: error: linker command failed with exit code 1 (use -v to see invocation)

2. When I add the -rpath-link to commandline, it links fine as expected:

/home/umb/LLVM/build/bin/clang -shared -fuse-ld=bfd -fPIC shared2.cpp -o shared2.so
/home/umb/LLVM/build/bin/clang -shared -fuse-ld=bfd -fPIC shared.cpp shared2.so -o shared.so
/home/umb/LLVM/build/bin/clang -fuse-ld=bfd main.cpp shared.so -o test -Wl,-rpath-link,/home/umb/tests/59rpath
<no errors here>

3. But at the same time if I link the same using gold then with or without -rpath-link, it is also fine for me.

/home/umb/LLVM/build/bin/clang -shared -fuse-ld=gold -fPIC shared2.cpp -o shared2.so
/home/umb/LLVM/build/bin/clang -shared -fuse-ld=gold -fPIC shared.cpp shared2.so -o shared.so
/home/umb/LLVM/build/bin/clang -fuse-ld=gold main.cpp shared.so -o test
<no errors here>
/home/umb/LLVM/build/bin/clang -shared -fuse-ld=gold -fPIC shared2.cpp -o shared2.so
/home/umb/LLVM/build/bin/clang -shared -fuse-ld=gold -fPIC shared.cpp shared2.so -o shared.so
/home/umb/LLVM/build/bin/clang -fuse-ld=gold main.cpp shared.so -o test -Wl,-rpath-link,/home/umb/tests/59rpath
<no errors here>

So I think we can ignore that in the same way as gold do. And that is 'natural' support in lld. I mean 'natural' is that we do not change anything
to have the same behavior.

[ruiu]

I agree with your argument that we should ignore that option. gold completely ignores that option, and the GNU ld's behavior to try to resolve undefined symbols in all shared object files at (static-)link time seems broken to me.

I don't think you need a test for this. Intended behavior of this patch is ignoring that option and it is trivially achieved by your change.

ELF/Options.td

190

I think both -rpath-link and --rpath-link are valid.

[grimar]

• Addressed review comments.

Patch reduced to trivial single line, that just ignores the option.

ELF/Options.td

190

Agree.
gold accepts both, ld only -rpath-link.
I think we dont miss anything if will either suport both variants.

[ruiu]

LGTM

ELF/Options.td

 def start_group_paren: Flag<["-"], "(">;
 
 // Options listed below are silently ignored for now for compatibility.
 def fatal_warnings : Flag<["--"], "fatal-warnings">;
 def no_add_needed : Flag<["--"], "no-add-needed">;
 def no_fatal_warnings : Flag<["--"], "no-fatal-warnings">;
 def no_warn_common : Flag<["--", "-"], "no-warn-common">;
 def no_warn_mismatch : Flag<["--"], "no-warn-mismatch">;
+def rpath_link : Separate<["-"], "rpath-link">;
 def version_script : Separate<["--"], "version-script">;
 def warn_shared_textrel : Flag<["--"], "warn-shared-textrel">;
 def G : Separate<["-"], "G">;
 
 // Aliases for ignored options
 def alias_version_script_version_script : Joined<["--"], "version-script=">, Alias<version_script>;
 
 // Debugging options
 def save_temps : Flag<["-"], "save-temps">;

test/ELF/Inputs/rpath-link.s

+.text
+.globl _Z1Av
+.type _Z1Av,@function
+_Z1Av:
+  callq _Z1Bv@PLT

test/ELF/Inputs/rpath-link2.s

+.text
+.globl _Z1Bv
+.type _Z1Bv,@function
+_Z1Bv:
+ retq

test/ELF/rpath-link.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %S/Inputs/rpath-link.s -o %tlink1.o
+# RUN: ld.lld -shared %tlink1.o -o %tlink1.so
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %S/Inputs/rpath-link2.s -o %tlink2.o
+# RUN: ld.lld -shared %tlink2.o %tlink1.so -o %tlink2.so
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t %tlink1.so -o %t.out
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t %tlink1.so -o %t.out -rpath-link write_whatever_you_want_here
+
+.text
+.globl _start
+_start:
+  callq _Z1Av