On Fri, Apr 10, 2020 at 06:03:38PM +0200, Ard Biesheuvel wrote: > On Fri, 10 Apr 2020 at 17:16, Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > > > On Fri, Apr 10, 2020 at 10:20:42AM +0200, Ard Biesheuvel wrote: > > > On Thu, 9 Apr 2020 at 23:08, Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > > > > > > > On Thu, Apr 09, 2020 at 04:53:07PM -0400, Brian Gerst wrote: > > > > > > Can we use the -fno-zero-initialized-in-bss compiler flag instead of > > > > > > explicitly marking global variables? > > > > > > > > > > Scratch that. Apparently it only works when a variable is explicitly > > > > > initialized to zero. > > > > > > > > > > -- > > > > > Brian Gerst > > > > > > > > Right, there doesn't seem to be a compiler option to turn off the use of > > > > .bss altogether. > > > > > > Yeah. I'll try to come up with a way to consolidate this a bit across > > > architectures (which is a bit easier now that all of the EFI stub C > > > code lives in the same place). It is probably easiest to use a section > > > renaming trick similar to the one I added for ARM (as Arvind suggested > > > as well, IIRC), and get rid of the per-symbol annotations altogether. > > > > Does that work for 32-bit ARM, or does it need to be .data to tell the > > compiler to avoid generating GOT references? If that's fine, we don't > > actually need to rename sections -- linker script magic is enough. For > > eg, the below pulls the EFI stub bss into .data for x86 without the need > > for the annotations. > > > > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S > > index 508cfa6828c5..e324819c95bc 100644 > > --- a/arch/x86/boot/compressed/vmlinux.lds.S > > +++ b/arch/x86/boot/compressed/vmlinux.lds.S > > @@ -52,6 +52,7 @@ SECTIONS > > _data = . ; > > *(.data) > > *(.data.*) > > + drivers/firmware/efi/libstub/lib.a:(.bss .bss.*) > > _edata = . ; > > } > > . = ALIGN(L1_CACHE_BYTES); > > No, we can add this to ARM as well, and get rid of the > __efistub_global annotations entirely. Cool. > > We'll still need .data.efistub for the .data pieces, but that is a > separate issue. You can avoid that by using an archive specification like above. i.e. adding drivers/firmware/efi/libstub/lib.a:(.data .data.*) to the .init.data output section will pull in just the .data input sections from the EFI stub into the .init.data section.
