Messages in this thread | | | Subject | Re: [PATCH] compiler-gcc: disable -ftracer for __noclone functions | From | Nadav Amit <> | Date | Tue, 8 May 2018 11:12:30 -0700 |
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Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 05/05/2018 19:22, Nadav Amit wrote: >> Paolo Bonzini <pbonzini@redhat.com> wrote: >> >>> -ftracer can duplicate asm blocks causing compilation to fail in >>> noclone functions. For example, KVM declares a global variable >>> in an asm like >>> >>> asm("2: ... \n >>> .pushsection data \n >>> .global vmx_return \n >>> vmx_return: .long 2b"); >>> >>> and -ftracer causes a double declaration. >>> >>> Cc: Andrew Morton <akpm@linux-foundation.org> >>> Cc: Michal Marek <mmarek@suse.cz> >>> Cc: stable@vger.kernel.org >>> Cc: kvm@vger.kernel.org >>> Reported-by: Linda Walsh <lkml@tlinx.org> >>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> >>> --- >>> include/linux/compiler-gcc.h | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h >>> index 22ab246feed3..eeae401a2412 100644 >>> --- a/include/linux/compiler-gcc.h >>> +++ b/include/linux/compiler-gcc.h >>> @@ -199,7 +199,7 @@ >>> #define unreachable() __builtin_unreachable() >>> >>> /* Mark a function definition as prohibited from being cloned. */ >>> -#define __noclone __attribute__((__noclone__)) >>> +#define __noclone __attribute__((__noclone__, __optimize__("no-tracer"))) >> >> [ Bringing the thread back from the dead for context ] >> >> Setting different optimization attributes to certain functions apparently >> prevents gcc from inlining functions with different “optimizations”. This >> results in poor compilation - most notably of vmx_vcpu_run() - and causes >> short functions such as to_vmx() not to be inlined. > > Hmm, I suppose we need to disable -fno-tracer globally... Has this > changed in recent versions of GCC?
I don’t think so. I played with optimization attributes of gcc some time ago and saw the same behavior. Unfortunately, I don’t easily find the place in gcc that implements this behavior.
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