2016-06-22 20:07 GMT+03:00 Dmitry Vyukov <dvyukov@xxxxxxxxxx>:
> When I build kernel with CONFIG_KASAN and gcc6 (which instruments globals
> and inserts global constructors and destructors), vmlinux contains some
> new unaccounted sections: .text.exit .text.startup .dtors.
> This messes vvar/percpu layout. Want:
>
> ffffffff822bfd80 D _edata
> ffffffff822c0000 D __vvar_beginning_hack
> ffffffff822c0000 A __vvar_page
> ffffffff822c0080 0000000000000098 D vsyscall_gtod_data
> ffffffff822c1000 A __init_begin
> ffffffff822c1000 D init_per_cpu__irq_stack_union
> ffffffff822c1000 A __per_cpu_load
> ffffffff822d3000 D init_per_cpu__gdt_page
>
> Got:
>
> ffffffff8279a600 D _edata
> ffffffff8279b000 A __vvar_page
> ffffffff8279c000 A __init_begin
> ffffffff8279c000 D init_per_cpu__irq_stack_union
> ffffffff8279c000 A __per_cpu_load
> ffffffff8279e000 D __vvar_beginning_hack
> ffffffff8279e080 0000000000000098 D vsyscall_gtod_data
> ffffffff827ae000 D init_per_cpu__gdt_page
>
> If my reading of the linker script is correct, this happens because
> __vvar_page and .vvar get different addresses here:
> //arch/x86/kernel/vmlinux.lds.S
>
> . = ALIGN(PAGE_SIZE);
> __vvar_page = .;
>
> .vvar : AT(ADDR(.vvar) - LOAD_OFFSET) {
> /* work around gold bug 13023 */
> __vvar_beginning_hack = .;
>
> Merge .text.exit into EXIT_TEXT, .text.startup into INIT_TEXT and
> .dtors into INIT_DATA.
>
> Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
>
> ---
>
> I can't say I fully understand what happens here, but it fixes my
> build and boot. I think we need something along these lines,
> but I am not sure about details.
Frankly, I don't understand why .text.[exit,startup] sections has any relation
to the bug you described, but maybe I just don't now linker
> ---
> include/asm-generic/vmlinux.lds.h | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 6a67ab9..6067d01 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -510,6 +510,7 @@
> #define KERNEL_CTORS() . = ALIGN(8); \
> VMLINUX_SYMBOL(__ctors_start) = .; \
> *(.ctors) \
> + *(.dtors) \
Why destructors added to constructors? We certainly don't want invoke
destructors on startup.
Actually, we can discard dtors section (and .fini_array too), as KASAN
destructors just call __asan_unregister_globals() which is nop,
and there is no other users of destructors in the kernel.
And how did you ended up with .dtors section anyway? I don't see it in
my build (gcc-6.1.0), and I though that recent gcc uses
.init_array and .fini_array instead of .ctor and .dtors respectively.
> *(SORT(.init_array.*)) \
> *(.init_array) \
> VMLINUX_SYMBOL(__ctors_end) = .;
> @@ -542,7 +543,9 @@
>
> #define INIT_TEXT \
> *(.init.text) \
> - MEM_DISCARD(init.text)
> + *(.text.startup) \
> + MEM_DISCARD(init.text) \
> + MEM_DISCARD(text.startup)
Why is .memtext.startup here? It shouldn't exist at all.
> #define EXIT_DATA \
> *(.exit.data) \
> @@ -551,7 +554,9 @@
>
> #define EXIT_TEXT \
> *(.exit.text) \
> - MEM_DISCARD(exit.text)
> + *(.text.exit) \
> + MEM_DISCARD(exit.text) \
> + MEM_DISCARD(text.exit)
>
ditto
> #define EXIT_CALL \
> *(.exitcall.exit)
> --
> 2.8.0.rc3.226.g39d4020
>
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