Messages in this thread | | | Date | Mon, 16 Mar 2020 14:26:48 +0100 | From | Jakub Jelinek <> | Subject | Re: [PATCH] x86: fix early boot crash on gcc-10 |
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On Mon, Mar 16, 2020 at 02:04:14PM +0100, Peter Zijlstra wrote: > > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > > index 9b294c13809a..da9f4ea9bf4c 100644 > > --- a/arch/x86/kernel/Makefile > > +++ b/arch/x86/kernel/Makefile > > @@ -11,6 +11,12 @@ extra-y += vmlinux.lds > > > > CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE) > > > > +# smpboot's init_secondary initializes stack canary. > > +# Make sure we don't emit stack checks before it's > > +# initialized. > > +nostackp := $(call cc-option, -fno-stack-protector) > > +CFLAGS_smpboot.o := $(nostackp) > > What makes GCC10 insert this while GCC9 does not. Also, I would much
My bet is different inlining decisions. If somebody hands me over the preprocessed source + gcc command line, I can have a look in detail (which exact change and why).
> rather GCC10 add a function attrbute to kill this: > > __attribute__((no_stack_protect))
There is no such attribute, only __attribute__((stack_protect)) which is meant mainly for -fstack-protector-explicit and does the opposite, or __attribute__((optimize ("no-stack-protector"))) (which will work only in GCC7+, since https://gcc.gnu.org/PR71585 changes). Or of course you could add noinline attribute to whatever got inlined and contains some array or addressable variable that whatever -fstack-protector* mode kernel uses triggers it. With -fstack-protector-all it would never work even in the past I believe.
Jakub
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