On Mon, Feb 12, 2024 at 1:30 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > +Cc: Fangrui Song <maskray@xxxxxxxxxx> > > > > On Thu, Feb 8, 2024 at 10:22 AM Yuxuan Shui <yshuiv7@xxxxxxxxx> wrote: > > > > NixOS is designed to have immutable packages, and explicit dependencies. > > It allows multiple different versions of the same shared library to > > co-exist in its file system. > > > > Each application built with Nix, the NixOS package manager, will have > > paths to its dependency shared libraries hardcoded into its executable, > > this includes the dynamic linker. To achieve this, Nix adds a > > --dynamic-linker linker flag when building any application. > > > > This isn't a problem if the kernel is built with ld.bfd, because ld.bfd > > ignores the --dynamic-linker flag when the resulting binary doesn't have > > a DT_NEEDED entry. However, ld.lld respects --dynamic-linker > > unconditionally, which breaks linking in several cases. > > > > This commit adds an explicit --no-dynamic-linker flag which overrides > > the flag added by Nix. > > > > I expect some Acks from LLVM folks (especially, from Frangrui) > if this is the right thing to do. GNU ld seems to ignore --dynamic-linker for a position-dependent executable (ET_EXEC) when there is no DT_NEEDED entry. ld.lld respects --dynamic-linker in this case. Before this kernel report, I do not know any user inconvenienced by this difference. (mold respects --dynamic-linker as well.) This could be helpful to test an executable with PT_INTERP but no DT_NEEDED. I think this patch does not fix non-x86 builds. It feels to me that NixOS should provide a linker wrapper that does not force --dynamic-linker=. While it's extremely uncommon (and generally not recommended), certain programs invoke the linker directly (instead of using a compiler driver). Such programs would run into a problem when they make a position-dependent executable with no dependency as well. I don't feel that NixOS forcing --dynamic-linker= is enough justification to change linkers. > > Signed-off-by: Yuxuan Shui <yshuiv7@xxxxxxxxx> > > --- > > Makefile | 3 +++ > > arch/x86/boot/Makefile | 2 +- > > arch/x86/realmode/rm/Makefile | 2 +- > > 3 files changed, 5 insertions(+), 2 deletions(-) > > > > diff --git a/Makefile b/Makefile > > index a171eafce2a3b..10ed19caecb1b 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -531,6 +531,9 @@ RUSTFLAGS_KERNEL = > > AFLAGS_KERNEL = > > LDFLAGS_vmlinux = > > > > +LDFLAGS_MODULE += --no-dynamic-linker > > +LDFLAGS_vmlinux += --no-dynamic-linker > > + > > # Use USERINCLUDE when you must reference the UAPI directories only. > > USERINCLUDE := \ > > -I$(srctree)/arch/$(SRCARCH)/include/uapi \ > > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile > > index 3cece19b74732..390a4604166eb 100644 > > --- a/arch/x86/boot/Makefile > > +++ b/arch/x86/boot/Makefile > > @@ -102,7 +102,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE > > AFLAGS_header.o += -I$(objtree)/$(obj) > > $(obj)/header.o: $(obj)/zoffset.h > > > > -LDFLAGS_setup.elf := -m elf_i386 -z noexecstack -T > > +LDFLAGS_setup.elf := --no-dynamic-linker -m elf_i386 -z noexecstack -T > > $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE > > $(call if_changed,ld) > > > > diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile > > index f614009d3e4e2..4b42006d9ce02 100644 > > --- a/arch/x86/realmode/rm/Makefile > > +++ b/arch/x86/realmode/rm/Makefile > > @@ -50,7 +50,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE > > targets += realmode.lds > > $(obj)/realmode.lds: $(obj)/pasyms.h > > > > -LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T > > +LDFLAGS_realmode.elf := --no-dynamic-linker -m elf_i386 --emit-relocs -T > > CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj) > > > > targets += realmode.elf > > -- > > 2.43.0 > > > > > -- > Best Regards > Masahiro Yamada > -- 宋方睿
