On Sun, 14 Jul 2019 16:35:33 +0200 Vasily Gorbik <gor@xxxxxxxxxxxxx> wrote: > On Fri, Jul 12, 2019 at 07:21:01PM +0200, Petr Tesarik wrote: > > Various tools determine the kernel version from a given binary by > > scanning for the Linux banner string. This does not work if the > > banner string is compressed, but we can link it once more into the > > uncompressed portion of bzImage. > > > > Signed-off-by: Petr Tesarik <ptesarik@xxxxxxxx> > > --- > > arch/s390/boot/compressed/Makefile | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile > > index fa529c5b4486..9bc4685477c5 100644 > > --- a/arch/s390/boot/compressed/Makefile > > +++ b/arch/s390/boot/compressed/Makefile > > @@ -11,6 +11,7 @@ UBSAN_SANITIZE := n > > KASAN_SANITIZE := n > > > > obj-y := $(if $(CONFIG_KERNEL_UNCOMPRESSED),,decompressor.o) piggy.o info.o > > +obj-y += ../../../../init/banner.o > > We don't reuse objects from another build stage, we rebuild them with > distinct decompressor's build flags. > $ git grep "ctype.[oc]" -- arch/s390/boot > arch/s390/boot/Makefile:obj-y += ctype.o text_dma.o > arch/s390/boot/ctype.c:#include "../../../lib/ctype.c" Those flags do not make a difference for a simple object file like the Linux banner, but I get your point, and I cannot see an issues with rebuilding the banner for the decompressor. > Besides that, there is a special CONFIG_KERNEL_UNCOMPRESSED mode, with > which "strings vmlinuz | grep 'Linux version'" I assume you are using > would still yield result. Adding the second version of banner would > produce duplicated result in this case. Sure, and AFAICT that's not a problem. But the point here is that the production kernel should be compressed for all those well-known reasons, but such image is then not recognized. > But even before discussing solutions I would like to understand the > problem first. Which specific tools are you referring to? What are they > good for? And how do they get the kernel version from other architectures > compressed images? The tool I'm aware of is called get_kernel_version. It's built as part of openSUSE aaa_base and is used at install time. I'm not quite sure how it is used, but I have added Raymund Will to Cc; he can provide more information. There's also an open bug for it: https://bugzilla.opensuse.org/show_bug.cgi?id=1139939 As for other architectures, I only know about x86. The x86 compressed binary contains a header with various pointers, among them a pointer to the kernel version string, so it must be added to the decompressor (cf. arch/x86/boot/version.c). If you prefer to have a similar header for other architectures, then that would be fine with me, but it's a bit more involved, because it would set up a new ABI... HTH, Petr T
