On Tue, Oct 17, 2017 at 5:34 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Tue, Oct 17, 2017 at 8:26 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> On Tue, Oct 17, 2017 at 8:23 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >>> On Tue, Oct 17, 2017 at 1:00 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >>>> Hi Kees, >>>> >>>> On my test box, current linux-next kernels fail to build due to the >>>> patch that introduces CONFIG_CC_STACKPROTECTOR_AUTO, with my mainline >>>> gcc >>>> builds up to gcc-5.5.0. gcc-6 and higher work fine, as >>>> scripts/gcc-x86_64-has-stack-protector.sh returns 'y' for those. >>>> >>>> Using the compilers provided by Ubuntu (4.6/4.7/4.8/4.9), everything >>>> also works as expected, so my interpretation is that mainline gcc did >>>> not enable the stack protector until gcc-6, while distributions did. >>>> >>>> Do you agree with that interpretation? >>> >>> It's probably a little different. I tried bisecting the gcc commit that fixed >>> the issue for me, and ended up with this commit >>> >>> https://gitlab.indel.ch/thirdparty/gcc/commit/c14bac81551d6769741c2b1cc55e04d94fe8d3a7 >>> >>> that caused the target to change from x86_64-unknown-linux to >>> x86_64-pc-linux, and apparently caused the compiler bootstrap >>> to incorrectly identify the capabilities of the assembler. As a result, >>> the assembler output inside of scripts/gcc-x86_64-has-stack-protector.sh >>> that should be >>> [snip] >> >> Yeah, %gs: vs __stack_chk_guard global. >> >> Do you know which gccs (of the past) had this? >> >> akpm's build error is different still, there are no warnings at all >> and then the build fails with missing __stack_chks. I'm still trying >> to figure that one out. > > Oh, I think I know what's happening. I'm going to try to simulate this > and send another patch for testing... > > (I'm still curious about the compiler versions, since my gcc 4.4.4 > works fine for stack-protector.) I've managed to reduce the change that fixed it to this bit in the compiler sources: index dbfb978..d5bc694 100755 --- a/config.guess +++ b/config.guess @@ -1021,7 +1021,7 @@ EOF echo ${UNAME_MACHINE}-dec-linux-${LIBC} exit ;; x86_64:Linux:*:*) - echo ${UNAME_MACHINE}-unknown-linux-${LIBC} + echo ${UNAME_MACHINE}-pc-linux-${LIBC} exit ;; xtensa*:Linux:*:*) echo ${UNAME_MACHINE}-unknown-linux-${LIBC} I still don't know why that makes a difference, but all versions prior to gcc-6.1 have the problem for me. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
