• Nadav Amit's avatar
    x86/bug: Macrofy the BUG table section handling, to work around GCC inlining bugs · f81f8ad5
    Nadav Amit authored
    As described in:
    
      77b0bf55: ("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs")
    
    GCC's inlining heuristics are broken with common asm() patterns used in
    kernel code, resulting in the effective disabling of inlining.
    
    The workaround is to set an assembly macro and call it from the inline
    assembly block. As a result GCC considers the inline assembly block as
    a single instruction. (Which it isn't, but that's the best we can get.)
    
    This patch increases the kernel size:
    
          text     data     bss      dec     hex  filename
      18146889 10225380 2957312 31329581 1de0d2d  ./vmlinux before
      18147336 10226688 2957312 31331336 1de1408  ./vmlinux after (+1755)
    
    But enables more aggressive inlining (and probably better branch decisions).
    
    The number of static text symbols in vmlinux is much lower:
    
     Before: 40218
     After:  40053 (-165)
    
    The assembly code gets harder to read due to the extra macro layer.
    
    [ mingo: Rewrote the changelog. ]
    Tested-by: default avatarKees Cook <keescook@chromium.org>
    Signed-off-by: default avatarNadav Amit <namit@vmware.com>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20181003213100.189959-7-namit@vmware.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    f81f8ad5
bug.h 7.1 KB