Hi Nick, On Fri, Apr 12, 2019 at 3:20 AM Nick Desaulniers <ndesaulni...@google.com> wrote: > > On Thu, Apr 11, 2019 at 2:30 AM Masahiro Yamada > <yamada.masah...@socionext.com> wrote: > > > > We use $(LD) to link vmlinux, modules, decompressors, etc. > > > > VDSO is the only exceptional case where $(CC) is used as the linker > > driver, but I do not know why we need to do so. VDSO uses a special > > linker script, and does not link standard libraries at all. > > > > I changed the Makefile to use $(LD) rather than $(CC). I tested this, > > and VDSO worked for me. > > > > Users will be able to use their favorite linker (e.g. lld instead of > > of bfd) by passing LD= from the command line. > > > > My plan is to rewrite all VDSO Makefiles to use $(LD), then delete > > cc-ldoption. > > > > Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com> > > --- > > > > arch/arm64/kernel/vdso/Makefile | 13 +++---------- > > 1 file changed, 3 insertions(+), 10 deletions(-) > > > > diff --git a/arch/arm64/kernel/vdso/Makefile > > b/arch/arm64/kernel/vdso/Makefile > > index a0af6bf6c11b..744b9dbaba03 100644 > > --- a/arch/arm64/kernel/vdso/Makefile > > +++ b/arch/arm64/kernel/vdso/Makefile > > @@ -12,17 +12,12 @@ obj-vdso := gettimeofday.o note.o sigreturn.o > > targets := $(obj-vdso) vdso.so vdso.so.dbg > > obj-vdso := $(addprefix $(obj)/, $(obj-vdso)) > > > > -ccflags-y := -shared -fno-common -fno-builtin > > Thanks for the patch; in general LGTM. Just some small questions: > > Looks like -shared and -fno-common are linker flags forwarded along, > but -fno-builtin is meant for the compiler, right?
Definitely, -shared must be passed to the linker to create a shared object. It is listed in the linker option list: https://gcc.gnu.org/onlinedocs/gcc-8.3.0/gcc/Link-Options.html#Link-Options I think -fno-common is a compiler flag instead of a linker one as far as I understand this: https://gcc.gnu.org/onlinedocs/gcc-8.3.0/gcc/Code-Gen-Options.html#Code-Gen-Options -fno-builtin is a compiler flag: https://gcc.gnu.org/onlinedocs/gcc-8.3.0/gcc/C-Dialect-Options.html#C-Dialect-Options > Do we want to keep > that in ccflags? All source files in arch/arm64/kernel/vdso/ are written in assembly (gettimeofday.S note.S sigreturn.S). So, -fno-common -fno-builtin for ccflags-y are not used. That's why I dropped them. If we want to keep them just in case, it is fine with me too. > I'm not sure why it would have been added > intentionally; maybe Will knows? Maybe it's ok to drop. They have been here since the initial VDSO support by commit 9031fefde6f2a. Will, do you remember why you added these flags? > > -ccflags-y += -nostdlib -Wl,-soname=linux-vdso.so.1 \ > > - $(call cc-ldoption, -Wl$(comma)--hash-style=sysv) > > +ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 \ > > + $(call ld-option, --hash-style=sysv) -n -T > > Forgive my ignorance, but the man page for ld makes it looks like the > -T argument requires a subsequent argument `scriptfile`. Is that what > `$(real-prereqs)` was doing below? If so, is dropping it in this patch > intentional? I just re-used cmd_ld in scripts/Makefile.lib It will be expanded like follows: cmd_ld = $(LD) $(ld_flags) $(real-prereqs) -o $@ -> $(LD) $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F)) $(real-prereqs) -o $@ -> $(LD) -shared -nostdlib -soname=linux-vdso.so.1 \ --hash-style=sysv -n -T \ $(obj)/vdso.lds $(obj-vdso) -o $(obj)/vdso.so.dbg -- Best Regards Masahiro Yamada
