| Message ID | 20181107003913.19061-1-pcc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Build vDSO with -ffixed-x18 | expand |
On Tue, Nov 06, 2018 at 04:39:13PM -0800, Peter Collingbourne wrote: > The vDSO needs to be build with x18 reserved in order to accommodate > userspace platform ABIs built on top of Linux that use the register > to carry inter-procedural state, as provided for by the AAPCS. > An example of such a platform ABI is the one that will be used by an > upcoming version of Android. > > Although this change is currently a no-op due to the fact that the vDSO > is currently implemented in pure assembly on arm64, it is necessary > in order to prepare for another change [1] that will add C code to > the vDSO. Since this is a no-op for the current kernel, I guess Vincenzo (cc'ed) will pick it up as he's planning to post an update to the vDSO in C series soon.
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile index b215c712d897..8cd4707f832a 100644 --- a/arch/arm64/kernel/vdso/Makefile +++ b/arch/arm64/kernel/vdso/Makefile @@ -12,7 +12,7 @@ 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 +ccflags-y := -shared -fno-common -fno-builtin -ffixed-x18 ccflags-y += -nostdlib -Wl,-soname=linux-vdso.so.1 \ $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
The vDSO needs to be build with x18 reserved in order to accommodate userspace platform ABIs built on top of Linux that use the register to carry inter-procedural state, as provided for by the AAPCS. An example of such a platform ABI is the one that will be used by an upcoming version of Android. Although this change is currently a no-op due to the fact that the vDSO is currently implemented in pure assembly on arm64, it is necessary in order to prepare for another change [1] that will add C code to the vDSO. [1] https://patchwork.kernel.org/patch/10044501/ Signed-off-by: Peter Collingbourne <pcc@google.com> Cc: Mark Salyzyn <salyzyn@google.com> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-arm-kernel@lists.infradead.org --- arch/arm64/kernel/vdso/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)