Hi, On Tue, Mar 28, 2017 at 12:00:15PM +0200, Dmitry Vyukov wrote: > On Tue, Mar 28, 2017 at 11:57 AM, Arnd Bergmann <[email protected]> wrote: > > I ran into a link error on ARM64 for lkdtm_rodata_do_nothing: > > > > drivers/misc/built-in.o: In function `lkdtm_rodata_do_nothing': > > :(.rodata+0x68c8): relocation truncated to fit: R_AARCH64_CALL26 against > > symbol `__sanitizer_cov_trace_pc' defined in .text section in > > kernel/built-in.o > > > > I did not analyze this further, but my theory is that we would need a > > trampoline > > to call __sanitizer_cov_trace_pc(), but the linker (correctly) only adds > > trampolines > > for callers in executable sections.
For reference, is this a "large" config, e.g. allyesconfig? I'm aware that at least as recently as GCC 6 there were issues with veneer generation for calls across sections (which I personally saw with calls from .init.text to .text) when the kernel was sufficiently large. FWIW, I have no problem building a v4.11-rc3 kernel with both KCOV and LKDTM using the Linaro 15.08 aarch64-linux-gnu GCC 5 toolchain. Which toolchain are you using? No strong feelings on this patch, but it may be indicative of a larger problem, and we probably don't want to play whack-a-mole to fix relocation truncation more generally. Thanks, Mark. > > Disabling KCOV for this one file avoids the build failure with no > > other practical downsides I can think of. > > > > The problem can only happen on kernels that contain both kcov and > > lkdtm, so if we want to backport this, it should be in the earliest > > version that has both (v4.8). > > > > Cc: Dmitry Vyukov <[email protected]> > > Cc: Kees Cook <[email protected]> > > Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") > > Fixes: 9a49a528dcf3 ("lkdtm: add function for testing .rodata section") > > Signed-off-by: Arnd Bergmann <[email protected]> > > --- > > drivers/misc/Makefile | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile > > index 4925ea8e1952..7a321047bfbe 100644 > > --- a/drivers/misc/Makefile > > +++ b/drivers/misc/Makefile > > @@ -63,6 +63,8 @@ lkdtm-$(CONFIG_LKDTM) += lkdtm_perms.o > > lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o > > lkdtm-$(CONFIG_LKDTM) += lkdtm_usercopy.o > > > > +KCOV_INSTRUMENT_lkdtm_rodata.o := n > > + > > OBJCOPYFLAGS := > > OBJCOPYFLAGS_lkdtm_rodata_objcopy.o := \ > > --set-section-flags .text=alloc,readonly \ > > -- > > 2.9.0 > > > Acked-by: Dmitry Vyukov <[email protected]>
