Date: Wed, 25 Dec 2019 20:46:37 -0800 From: Fangrui Song <i@...kray.me> To: Youren Shen <shenyouren@...il.com> Cc: Rich Felker <dalias@...c.org>, musl@...ts.openwall.com Subject: Re: [BUG] Force to use a dynamic linker in musl-clang wapper cause a crash for static-pie c++ programs. >On Tue, Dec 24, 2019 at 11:03 PM Rich Felker <dalias@...c.org> wrote: > > On Tue, Dec 24, 2019 at 10:38:49PM +0800, Youren Shen wrote: > > Hey, there, > > Recently I'm trying to build a non-gnu toolchain with musl, clang, llvm, > > libc++, compiler-rt. While static-pie feature is very useful in our > > project, musl-clang force to link a dynamic linker into the binary. This > > behavior will cause a crash in c++ programs with compiler-rt and libc++. > > For more details and reproduction of this bug, you can read my previous > > email to llvm-dev mail lists. > > I spend a few days to find the reason -- in function _dlstart_c, the > > program will get a "base" of relocation in /lib/ld-musl-x86_64.so.1, > which > > is not right when it tries to relocate .rel.dyn section in the binary. > > Overall, the static-pie program does not need a dynamic linker at all. So > > maybe we should remove this argument in wrapper when static-pie is > enabled. > > > > Thank you very much. > > > > . https://groups.google.com/forum/#!msg/llvm-dev/XPrSPqD2zjM/ > YtH6Fi2YAgAJ > > I don't think the wrappers (gcc or clang one) have been updated with > logic for static pie since it was added, and I'm not sure how easy it > is to add. I'd welcome patches for review, though. > > Rich > > Thanks for your reply. > > Dived deeper, I think this is because the options clang/gcc passed to ld are > not well handled by ld. Unlike "-static", which is passed directly to the > linker, the clang pass -no-dynamic-linker when static-pie is enabled. However, > -dynamic-linker=<file> in ld.musl-clang wrapper conflict with this > -no-dynamic-linker. As a result, ld accepts the last one it received, which is > "-dynamic-linker=<file>" in this case. Here is the problem: even we passed > static-pie to clang, and then the clang pass -no-dynamic-linker to ld, This > option is still omitted by ld.musl-clang. I suggest a fix on it: move > -dynamic-linker "$ldso" before the previous user inputs. > Before: > ``` > exec $($cc -print-prog-name=ld) -nostdlib "$@" -lc -dynamic-linker "$ldso" > ``` > After: > ``` > exec $($cc -print-prog-name=ld) -nostdlib -dynamic-linker "$ldso" "$@" -lc > ``` > As you can see, this is a quite simple patch. Further testes may required. And > for musl-gcc, as I test, it seems that it has the same problem. But I'm not > familiar with gcc specs file. So maybe if anyone encounter the same problem, > they can refer this email and give a solution. It may be better moving -dynamic-linker from ld.musl-clang to musl-clang. For -shared, -static, and -static-pie, gcc specs does not pass -dynamic-linker. musl-clang should not pass -dynamic-linker if one of -shared, -static, -static-pie is used. (I think the ideal solution is not to have any platform-dependent default ld.so path (if GNU ld had done this, there would have been no point to have --no-dynamic-linker in the first place). Let -dynamic-linker create .interp . See https://reviews.llvm.org/D62765) [-Wunused-command-line-argument] is another issue: % ~/musl/Debug/obj/musl-clang a.c -c clang: warning: argument unused during compilation: '-fuse-ld=musl-clang' [-Wunused-command-line-argument] clang: warning: argument unused during compilation: '-static-libgcc' [-Wunused-command-line-argument] clang: warning: argument unused during compilation: '-L-user-start' [-Wunused-command-line-argument] clang: warning: argument unused during compilation: '-L/home/ray/.local/stow/musl/lib' [-Wunused-command-line-argument] clang: warning: argument unused during compilation: '-L-user-end' [-Wunused-command-line-argument] Adding a default -Wno-unused-command-line-argument may be a solution.
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