+++ Ard Biesheuvel [24/01/17 16:16 +0000]:
This v4 is a followup to [0] 'modversions: redefine kcrctab entries as relative CRC pointers', but since relative CRC pointers do not work in modules, and are actually only needed by powerpc with CONFIG_RELOCATABLE=y, I have made it a Kconfig selectable feature instead. Patch #1 introduces the MODULE_REL_CRCS Kconfig symbol, and adds the kbuild handling of it, i.e., modpost, genksyms and kallsyms. Patch #2 switches all architectures to 32-bit CRC entries in kcrctab, where all architectures except powerpc with CONFIG_RELOCATABLE=y use absolute ELF symbol references as before. v4: make relative CRCs kconfig selectable use absolute CRC symbols in modules regardless of kconfig selection split into two patches
This asymmetry threw me off a bit, especially the Kconfig naming (only vmlinux crcs get the relative offsets, and only on powerpc atm, but all modules keep the absolute syms, but it is called MODULE_REL_CRCS...), if we keep this asymmetric crc treatment, it would be really nice to note this discrepancy this somewhere, perhaps in the Kconfig, to keep our heads from spinning :-) I'm still catching up on the previous discussion threads, but can you explain a bit more why you switched away from full blown relative crcs from your last patchset [1]? I had lightly tested your v3 on ppc64le previously, and relative offsets with modules seemed to worked very well. I'm probably missing something very obvious. [1] http://marc.info/?l=linux-arch&m=148493613415294&w=2
v3: emit CRCs into .rodata rather than .rodata.modver, given that the latter will be emitted with read-write permissions, making the CRCs end up in a writable module segment. fold the modpost fix to ensure that the section address is only substracted from the symbol address when the ELF object in question is fully linked (i.e., ET_DYN or ET_EXEC, and not ET_REL) v2: update modpost as well, so that genksyms no longer has to emit symbols for both the actual CRC value and the reference to where it is stored in the image [0] http://marc.info/?l=linux-arch&m=148493613415294&w=2 Ard Biesheuvel (2): kbuild: modversions: add infrastructure for emitting relative CRCs modversions: treat symbol CRCs as 32 bit quantities arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/module.h | 4 -- arch/powerpc/kernel/module_64.c | 8 ---- include/asm-generic/export.h | 11 ++--- include/linux/export.h | 14 ++++++ include/linux/module.h | 14 +++--- init/Kconfig | 4 ++ kernel/module.c | 45 ++++++++++---------- scripts/Makefile.build | 2 + scripts/genksyms/genksyms.c | 19 ++++++--- scripts/kallsyms.c | 12 ++++++ scripts/mod/modpost.c | 10 +++++ 12 files changed, 93 insertions(+), 51 deletions(-) -- 2.7.4
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