* Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > Eliminate all GOT entries in the decompressor binary, by forcing hidden > visibility for all symbol references, which informs the compiler that > such references will be resolved at link time without the need for > allocating GOT entries. > > To ensure that no GOT entries will creep back in, add an assertion to > the decompressor linker script that will fire if the .got section has > a non-zero size. > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > arch/x86/boot/compressed/Makefile | 1 + > arch/x86/boot/compressed/hidden.h | 19 +++++++++++++++++++ > arch/x86/boot/compressed/vmlinux.lds.S | 1 + > 3 files changed, 21 insertions(+) > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > index 5f7c262bcc99..aa9ed814e5fa 100644 > --- a/arch/x86/boot/compressed/Makefile > +++ b/arch/x86/boot/compressed/Makefile > @@ -40,6 +40,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, gnu) > KBUILD_CFLAGS += -Wno-pointer-sign > KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > +KBUILD_CFLAGS += -include hidden.h > + * When building position independent code with GCC using the -fPIC option, > + * (or even the -fPIE one on older versions), it will assume that we are > + * building a dynamic object (either a shared library or an executable) that > + * may have symbol references that can only be resolved at load time. For a > + * variety of reasons (ELF symbol preemption, the CoW footprint of the section > + * that is modified by the loader), this results in all references to symbols > + * with external linkage to go via entries in the Global Offset Table (GOT), > + * which carries absolute addresses which need to be fixed up when the > + * executable image is loaded at an offset which is different from its link > + * time offset. > + * > + * Fortunately, there is a way to inform the compiler that such symbol > + * references will be satisfied at link time rather than at load time, by > + * giving them 'hidden' visibility. > + */ > + > +#pragma GCC visibility push(hidden) BTW., how many such GOT entries did we have before this change, on a typical kernel? > +ASSERT (SIZEOF(.got) == 0, "Unexpected GOT entries detected!") s/ASSERT ( /ASSERT( Thanks, Ingo
