On Tue, May 15, 2018 at 7:11 AM, Nadav Amit <[email protected]> wrote: > GCC considers the number of statements in inlined assembly blocks, > according to new-lines and semicolons, as an indication to the cost of > the block in time and space. This data is distorted by the kernel code, > which puts information in alternative sections. As a result, the > compiler may perform incorrect inlining and branch optimizations. > > The solution is to set an assembly macro and call it from the inlined > assembly block. As a result GCC considers the inline assembly block as > a single instruction. > > This patch allows to inline functions such as __get_seccomp_filter(). > The effect of the patch is as follows on the kernel size: > > text data bss dec hex filename > 18146418 10064100 2936832 31147350 1db4556 ./vmlinux before > 18148228 10063968 2936832 31149028 1db4be4 ./vmlinux after (+1678) > > Static text symbols: > Before: 39673 > After: 39649 (-24) > > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: [email protected] > Cc: Kees Cook <[email protected]> > Cc: Jan Beulich <[email protected]> > Cc: Josh Poimboeuf <[email protected]> > > Signed-off-by: Nadav Amit <[email protected]> > --- > arch/x86/include/asm/refcount.h | 55 ++++++++++++++++++++------------- > 1 file changed, 33 insertions(+), 22 deletions(-) > > diff --git a/arch/x86/include/asm/refcount.h b/arch/x86/include/asm/refcount.h > index 4cf11d88d3b3..a668c534206d 100644 > --- a/arch/x86/include/asm/refcount.h > +++ b/arch/x86/include/asm/refcount.h > @@ -14,34 +14,43 @@ > * central refcount exception. The fixup address for the exception points > * back to the regular execution flow in .text. > */ > -#define _REFCOUNT_EXCEPTION \ > - ".pushsection .text..refcount\n" \ > - "111:\tlea %[counter], %%" _ASM_CX "\n" \ > - "112:\t" ASM_UD2 "\n" \ > - ASM_UNREACHABLE \ > - ".popsection\n" \ > - "113:\n" \ > + > +asm ("\n" > + ".macro __REFCOUNT_EXCEPTION counter:vararg\n\t"
Why are these vararg? Also, I think for the whole series, these #define-a-macro cases need a comment in the code. It's not obvious from looking at the code why they've defined a macro instead of just leaving the asm as it was. Beyond that, as long as there is no behavioral changes, I'm fine with the changes. -Kees -- Kees Cook Pixel Security
