gcc version checks

[goldyfruit]

Hi,

I try to use kpatch on Debian GNU/Linux Wheezy with a 3.14.5 kernel. The kernel compilation works but when kpatch-build try to create the patch, it fail !

+ /usr/local/libexec/kpatch/create-diff-object orig/fs/proc/meminfo.o patched/fs/proc/meminfo.o /usr/lib/debug/lib/modules/3.14.5-kpatch/vmlinux output/fs/proc/meminfo.o
+ tee -a /tmp/kpatch-build-1402941756.log
meminfo.o: meminfo.o: changed section .rela.text not selected for inclusion
meminfo.o: meminfo.o: changed section .rodata.str1.8 not selected for inclusion
meminfo.o: 2 unsupported section change(s)
/usr/local/libexec/kpatch/create-diff-object: unreconcilable difference
+ [[ 2 -eq 0 ]]
+ die
+ [[ -z '' ]]
+ echo 'ERROR: kpatch build failed. Check /tmp/kpatch-build-1402941756.log for more details.'
ERROR: kpatch build failed. Check /tmp/kpatch-build-1402941756.log for more details.
+ exit 1
+ cleanup
+ [[ 1 -eq 0 ]]
+ [[ -e /media/.kpatch/src/applied-patch ]]

The command line used : kpatch-build -s /usr/src/linux-source-3.14.5-kpatch -c /boot/config-3.14.5-kpatch -d meminfo-string.patch

I found some discussions about .rela. issues but everytime it's fixed by a commit. I use the last kpatch version.

Thanks for your help.

[sjenning]

@goldyfruit can you provide the patch you are using?

[goldyfruit]

@Spartacus06 i use the patch in the example

--- linux-source-3.14/fs/proc/meminfo.c 2014-05-31 15:34:37.000000000 -0400
+++ meminfo.c   2014-06-12 14:24:48.301835424 -0400
@@ -131,7 +131,7 @@
                "Committed_AS:   %8lu kB\n"
                "VmallocTotal:   %8lu kB\n"
                "VmallocUsed:    %8lu kB\n"
-               "VmallocChunk:   %8lu kB\n"
+               "VMALLOCCHUNK:   %8lu kB\n"
 #ifdef CONFIG_MEMORY_FAILURE
                "HardwareCorrupted: %5lu kB\n"
 #endif

[jpoimboe]

@goldyfruit This is a weird error, since kpatch-build should have no problem building this patch. Can you pull the latest master branch, recreate with the -d option added to kpatch-build, and put the resulting /tmp/kpatch-build-*.log file somewhere we can download it?

[flaming-toast]

@goldyfruit What version of gcc are you using? I tried this on a vanilla Debian wheezy installation and was able to reproduce the error. Turns out that gcc 4.7.2 (the version of gcc bundled with wheezy) won't compile the changed objects with -ffunction-sections and -pg flags used together ("warning: -ffunction-sections disabled; it makes profiling impossible"). It's been noted as an issue (https://gcc.gnu.org/ml/gcc-help/2008-11/msg00128.html) and was patched in a later version of gcc. Updating gcc fixed the issue. kpatch-build should probably fail if that warning comes up :-) though I'm not sure how to force the build to fail for that particular warning.

[jpoimboe]

Ah, thanks @goldyfruit . Maybe we can detect the gcc version and refuse to build on older versions.

[jpoimboe]

Guess we need to update the README too, which says that "gcc >= 4.6" is supported.

[jpoimboe]

sorry, thanks @flaming-toast :-)

[jpoimboe]

Ideally we would also enforce that the gcc version is the same as the one used to build the original kernel, which should be pretty easy:

[master] ~/git/kpatch $ gcc --version |head -n1
gcc (GCC) 4.8.2 20131212 (Red Hat 4.8.2-7)
[master] ~/git/kpatch $ strings /usr/lib/debug/lib/modules/3.14.8-200.fc20.x86_64/vmlinux |grep "GCC:"
GCC: (GNU) 4.8.2 20131212 (Red Hat 4.8.2-7)

[flaming-toast]

@jpoimboe Np. :-) Looks like the patch was merged in with the 4.8.0 release, so it should be safe to say something like "gcc >= 4.8"

[goldyfruit]

@flaming-toast Yes, with GCC 4.8 it works !
@jpoimboe I think that it's a good thing to add a GCC check.

Thanks guys.

[jpoimboe]

Reopening so we don't forget to add the gcc checks

[goldyfruit]

@jpoimboe Right !