On 12/13/21 11:36 AM, Christophe Leroy wrote:

Le 13/12/2021 à 15:47, Joe Lawrence a écrit :

quoted

On 12/13/21 2:42 AM, Christophe Leroy wrote:

quoted

Hello Joe,

I'm implementing LIVEPATCH on PPC32 and I wanted to test with
STRICT_MODULE_RWX enabled so I took your branch as suggested, but I'm
getting the following errors on build. What shall I do ?

    CALL    scripts/checksyscalls.sh
    CALL    scripts/atomic/check-atomics.sh
    CHK     include/generated/compile.h
    KLP     lib/livepatch/test_klp_convert1.ko
klp-convert: section .rela.klp.module_relocs.test_klp_convert_mod length
beyond nr_entries

klp-convert: Unable to load user-provided sympos
make[2]: *** [scripts/Makefile.modfinal:79:
lib/livepatch/test_klp_convert1.ko] Error 255
    KLP     lib/livepatch/test_klp_convert2.ko
klp-convert: section .rela.klp.module_relocs.test_klp_convert_mod length
beyond nr_entries

klp-convert: Unable to load user-provided sympos
make[2]: *** [scripts/Makefile.modfinal:79:
lib/livepatch/test_klp_convert2.ko] Error 255
    KLP     lib/livepatch/test_klp_convert_sections.ko
klp-convert: section .rela.klp.module_relocs.test_klp_convert_mod length
beyond nr_entries

klp-convert: Unable to load user-provided sympos
make[2]: *** [scripts/Makefile.modfinal:79:
lib/livepatch/test_klp_convert_sections.ko] Error 255
make[2]: Target '__modfinal' not remade because of errors.
make[1]: *** [scripts/Makefile.modpost:145: __modpost] Error 2
make: *** [Makefile:1770: modules] Error 2

Hi Christophe,

Interesting failure mode.  That's klp-convert complaining that it found
more relocations in a .klp.module_relocs.<objname> section than
expected, i.e. nr_entries = sec->size / sizeof(struct klp_module_reloc).

A few possibilities: the ELF sec->size was incorrectly set/read by
build/libelf (I doubt that).  Or maybe the layout/size of struct
klp_module_reloc is not consistent between kernel and userspace (I'm
more suspicious of this).

Can you post a copy of the build's symbols.klp and
lib/livepatch/test_klp_convert1.tmp.ko somewhere?  I should be able to
start debug with those files.

I sent you both files off list.

It looks like klp-convert doesn't use the correct size. It finds a 
struct of size 12 hence 3 entries for a section of size 40.

On PPC32 the struct has size 8 (void * is 4 and int is 4).

But I'm cross-building from x86_64 where the struct is 8 + 4 = 12.

Can it be the reason ?

I'm pretty sure that is it.  I haven't had much runtime with klp-convert
and cross-building (I've only found one big/little endian bug with
x86_64->s390x) and was going to ask you how you were testing :)

Do you know if there are other kernel build tools that deal with similar
situations?  This seems like a tricky job for the userspace build tool
to determine non-native target struct layout.

In the meantime, hacking in:

 struct klp_module_reloc {
-       void *sym;
+       uint32_t sym;
        unsigned int sympos;
 } __packed;

gets me generating an output .ko file, but the readelf output doesn't
look right.

I'll add this to the patchset TODO list, but may not get to it for a
while -- is there any chance the above hack works or could you test a
local non-cross build?

Thanks,

-- 
Joe