On Tue, Apr 11, 2017 at 01:28:45PM +0200, Ingo Molnar wrote:
>
> * Kirill A. Shutemov <kir...@shutemov.name> wrote:
>
> > On Tue, Apr 11, 2017 at 09:02:03AM +0200, Ingo Molnar wrote:
> > > I realize that you had difficulties converting this to C, but it's not
> > > going to
> > > get any easier in the future either, with one more paging mode/level
> > > added!
> > >
> > > If you are stuck on where it breaks I'd suggest doing it gradually: first
> > > add a
> > > trivial .c, build and link it in and call it separately. Then once that
> > > works,
> > > move functionality from asm to C step by step and test it at every step.
> >
> > I've described the specific issue with converting this code to C in cover
> > letter: how to make compiler to generate 32-bit code for a specific
> > function or translation unit, without breaking linking afterwards (-m32
> > break it).
>
> Have you tried putting it into a separate .c file, and building it 32-bit?
Yes, I have. The patch below fails linking:
ld: i386 architecture of input file `arch/x86/boot/compressed/head64.o' is
incompatible with i386:x86-64 output
>
> I think arch/x86/entry/vdso/Makefile contains an example of how to build
> 32-bit
> code even on 64-bit kernels.
I'll look closer (building proccess it's rather complicated), but my
understanding is that VDSO is stand-alone binary and doesn't really links
with the rest of the kernel, rather included as blob, no?
Andy, may be you have an idea?
diff --git a/arch/x86/boot/compressed/Makefile
b/arch/x86/boot/compressed/Makefile
index 44163e8c3868..8c1acacf408e 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -76,6 +76,8 @@ vmlinux-objs-$(CONFIG_EARLY_PRINTK) +=
$(obj)/early_serial_console.o
vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
ifdef CONFIG_X86_64
vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/pagetable.o
+ vmlinux-objs-y += $(obj)/head64.o
+$(obj)/head64.o: KBUILD_CFLAGS := -m32 -D__KERNEL__ -O2
endif
$(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
diff --git a/arch/x86/boot/compressed/head64.c
b/arch/x86/boot/compressed/head64.c
new file mode 100644
index 000000000000..42e1d64a15f4
--- /dev/null
+++ b/arch/x86/boot/compressed/head64.c
@@ -0,0 +1,3 @@
+void __startup32(void)
+{
+}
--
Kirill A. Shutemov
