[llvm-bugs] [Bug 37473] New: objcopy and strip get rid of the GNU_RELRO program header for binaries produced by lld

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37473

            Bug ID: 37473
           Summary: objcopy and strip get rid of the GNU_RELRO program
                    header for binaries produced by lld
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: ELF
          Assignee: unassignedbugs at nondot.org
          Reporter: ppadevski at gmail.com
                CC: llvm-bugs at lists.llvm.org

Suppose I have 3 files - f.h, f.cpp and main.cpp. I can add the contents if
necessary. I want to use full RELRO. checkrelro.sh comes from here
http://www.trapkit.de/tools/checkrelro.sh

>mkdir -p build

>
>./c++ -o build/main.o -c -g -fPIC main.cpp
>./c++ -o build/foo.o -c -g -fPIC foo.cpp
>./c++ -o build/libfoo.so -Wl,--hash-style=gnu -Wl,-O2 -Wl,-z,relro -Wl,-z,now -shared build/foo.o
>./c++ -o build/a.out -pie -Wl,--hash-style=gnu -Wl,-O2 -Wl,-z,relro -Wl,-z,now build/main.o -Lbuild -lfoo

>
>
>./checkrelro.sh --file build/libfoo.so

>
>echo 'objcopy --only-keep-debug'
>objcopy --only-keep-debug build/libfoo.so build/libfoo.so.debug
>./checkrelro.sh --file build/libfoo.so

>
>echo 'objcopy -R .gnu_debuglink'
>objcopy -R .gnu_debuglink --add-gnu-debuglink=build/libfoo.so.debug build/libfoo.so
>./checkrelro.sh --file build/libfoo.so

>
>echo 'strip'
>strip build/libfoo.so -o build/libfoo.so.stripped
>./checkrelro.sh --file build/libfoo.so
>./checkrelro.sh --file build/libfoo.so.stripped

>
>
>./checkrelro.sh --file build/a.out

>
>echo 'objcopy --only-keep-debug'
>objcopy --only-keep-debug build/a.out build/a.out.debug
>./checkrelro.sh --file build/a.out

>
>echo 'objcopy -R .gnu_debuglink'
>objcopy -R .gnu_debuglink --add-gnu-debuglink=build/a.out.debug build/a.out
>./checkrelro.sh --file build/a.out

>
>echo 'strip'
>strip build/a.out -o build/a.out.stripped
>./checkrelro.sh --file build/a.out
>./checkrelro.sh --file build/a.out.stripped


With gcc 6.4 and ld.bfd I get

> build/libfoo.so - full RELRO
> objcopy --only-keep-debug
> build/libfoo.so - full RELRO
> objcopy -R .gnu_debuglink
> build/libfoo.so - full RELRO
> strip
> build/libfoo.so - full RELRO
> build/libfoo.so.stripped - full RELRO
> build/a.out - full RELRO
> objcopy --only-keep-debug
> build/a.out - full RELRO
> objcopy -R .gnu_debuglink
> build/a.out - full RELRO
> strip
> build/a.out - full RELRO
> build/a.out.stripped - full RELRO


With gcc 6.4 and ld.lld I get

> build/libfoo.so - full RELRO
> objcopy --only-keep-debug
> build/libfoo.so - full RELRO
> objcopy -R .gnu_debuglink
> build/libfoo.so - no RELRO
> strip
> build/libfoo.so - no RELRO
> build/libfoo.so.stripped - no RELRO
> build/a.out - full RELRO
> objcopy --only-keep-debug
> build/a.out - full RELRO
> objcopy -R .gnu_debuglink
> build/a.out - no RELRO
> strip
> build/a.out - no RELRO
> build/a.out.stripped - no RELRO


It seems that both objcopy and strip get rid of the GNU_RELRO program header
which is very very unfortunate. Is there a remedy for that?

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