Hi Nick, On Tue, Apr 2, 2019 at 12:54 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Sat, Feb 16, 2019 at 10:09 AM Masahiro Yamada > <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > > > On Thu, Feb 14, 2019 at 8:08 AM Nick Desaulniers > > <ndesaulniers@xxxxxxxxxx> wrote: > > > > > > On Wed, Feb 13, 2019 at 6:59 AM Masahiro Yamada > > > <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > > > > > > > On Tue, Feb 12, 2019 at 5:42 AM <ndesaulniers@xxxxxxxxxx> wrote: > > > > > > > > > > This is needed because clang doesn't select which linker to use based on > > > > > $LD but rather -fuse-ld=lld. This is problematic especially for > > > > > cc-ldoption, which checks for linker flag support via invoking the > > > > > compiler, rather than the linker. > > > > > > > > > > > > Sorry, please explain what kind of problem > > > > this patch solves. > > > > > > > > > > > > > > > > [1] $(LD) is used to link vmlinux, modules, etc. > > > > > > > > [2] $(CC) is used to link vdso, etc. > > > > and -fuse-ld= selects which linker is invoked from $(CC) > > > > > > It solves case 2. > > > > > > > > > > > > > > > Is it a problem to use a different > > > > type of linker for [1] and [2] ? > > > > > > Ideally, no, but I can think of at least one case where it might be > > > problematic to mix linkers like that: > > > You might be mixing linker flags added via ld-option from one linker > > > that aren't actually supported by the other linker. > > > > You can do this only when you are sure > > that the _exactly_ same linker is used. > > > > In my understanding, -fuse-ld=lld does not guarantee it. > > I really don't think we should be mixing and matching linkers during a > kernel build. When we compile with clang, we don't have escape > hatches that allow for some object files to be compiled with GCC > (mixing clang and GCC compiled object files into one build). > Following the same logic, I think mixing linkers during kernel build > should similarly be dissuaded. This patch AVOIDS clang using a > different linker than what was specified via $LD, which is CRITICAL > for cc-ldoption kbuild macro. Masahiro, I hope this patch can be > re-evaluated, or if I'm not understanding your point, that you can > provide additional clarification. > You can pass an absolute pass to LD, like make LD=/path/to/my/llvm/install/dir/bin/ld.lld This clarifies which linker is being used even when multiple versions of llvm are installed on the machine. However, -fuse-ld=lld is ambiguous. Will it use the first ld.lld found in PATH? So, you cannot avoid mixing linkers by this means. If we could do -fuse=$(LD), I would agree with it. Clang accepts -fuse=<absolute-path>, GCC does not. Is there a way to control the linker search path? -- Best Regards Masahiro Yamada
