Messages in this thread | | | Date | Wed, 25 Sep 2019 12:20:41 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86, realmode: explicitly set entry via command line |
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+ some more people who did the unified realmode thing.
On Tue, Sep 24, 2019 at 12:33:08PM -0700, Nick Desaulniers wrote: > Linking with ld.lld via $ make LD=ld.lld produces the warning: > ld.lld: warning: cannot find entry symbol _start; defaulting to 0x1000 > > Linking with ld.bfd shows the default entry is 0x1000: > $ readelf -h arch/x86/realmode/rm/realmode.elf | grep Entry > Entry point address: 0x1000 > > While ld.lld is being pedantic, just set the entry point explicitly, > instead of depending on the implicit default. > > Link: https://github.com/ClangBuiltLinux/linux/issues/216 > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Changes V1 -> V2: > * Use command line flag, rather than linker script, as ld.bfd produces a > syntax error for `ENTRY(0x1000)` but is happy with `-e 0x1000` > > arch/x86/realmode/rm/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile > index f60501a384f9..338a00c5257f 100644 > --- a/arch/x86/realmode/rm/Makefile > +++ b/arch/x86/realmode/rm/Makefile > @@ -46,7 +46,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE > targets += realmode.lds > $(obj)/realmode.lds: $(obj)/pasyms.h > > -LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T > +LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -e 0x1000 -T
So looking at arch/x86/realmode/rm/realmode.lds.S: what's stopping people from adding more sections before the first
. = ALIGN(PAGE_SIZE);
which, with enough bytes to go above the first 4K, would cause that alignment to go to 0x2000 and then your hardcoded address would be wrong, all of a sudden.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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