[PATCH] stackprotector: fix multi-word cross-builds

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> 
> * Tejun Heo <tj@xxxxxxxxxx> wrote:
> 
> > Ingo Molnar wrote:
> > >>> I'll try other compilers but which version are you using?  The
> > >>> difference is that before the patchset, -fno-stack-protector was
> > >>> always added whether stackprotector was enabled or not so this problem
> > >>> wasn't visible (at the cost of bogus stackprotector of course).  We'll
> > >>> probably need to add __stack_chk_guard or disable if gcc generates
> > >>> such symbol.  I'll play with different gccs.
> > >> Can't reproduce with gcc-4.1 or 4.2.  Any chance you're using distcc
> > >> w/ a build machine w/ glibc < 2.4?  __stack_chk_guard is the symbol
> > >> gcc fetches stack canary from if TLS is not supported, so somehow gcc
> > >> thought that TLS wasn't available while building head64.
> > > 
> > > yeah - i also used distcc. Maybe the nostackp makefile magic gets confused
> > > about that?
> > 
> > It seems that even with the same gcc versions, gcc built against libc
> > w/o TLS support generates __stack_chk_guard, so if you mix the two
> > flavors, the has-stack-protector check can be compiled on machines w/
> > TLS while some other files end up being built on machines w/o TLS
> > support thus circumventing the support check.  Can you please see
> > whether non-distcc build fails too?
> 
> That build succeeds:
> 
> rhea:~/tip> make -j30 bzImage ARCH=x86_64 CROSS_COMPILE='/opt/crosstool/gcc-4.2.3-glibc-2.3.6/x86_64-unknown-linux-gnu/bin/x86_64-unknown-linux-gnu-'
> /home/mingo/tip/arch/x86/Makefile:82: stack protector enabled but no compiler support
>   CHK     include/linux/version.h
> [...]
> BFD: arch/x86/boot/compressed/vmlinux.bin: warning: allocated section `.bss' not in segment
> [...]
> Root device is (8, 3)
> Setup is 11996 bytes (padded to 12288 bytes).
> System is 5690 kB
> CRC be1b2e21
> Kernel: arch/x86/boot/bzImage is ready  (#3)
> 
> Some shell variable expansion bug? If CROSS_COMPILE is not a single word
> we fail to detect the compiler borkage at arch/x86/Makefile line 82?

Yep - i'm testing the fix below now - it's looking good so far.

	Ingo

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