• Josh Poimboeuf's avatar
    objtool: Support GCC 8 '-fnoreorder-functions' · 0bcba956
    Josh Poimboeuf authored
    [ Upstream commit 08b393d0 ]
    
    Since the following commit:
    
      cd77849a ("objtool: Fix GCC 8 cold subfunction detection for aliased functions")
    
    ... if the kernel is built with EXTRA_CFLAGS='-fno-reorder-functions',
    objtool can get stuck in an infinite loop.
    
    That flag causes the new GCC 8 cold subfunctions to be placed in .text
    instead of .text.unlikely.  But it also has an unfortunate quirk: in the
    symbol table, the subfunction (e.g., nmi_panic.cold.7) is nested inside
    the parent (nmi_panic).
    
    That function overlap confuses objtool, and causes it to get into an
    infinite loop in next_insn_same_func().  Here's Allan's description of
    the loop:
    
      "Objtool iterates through the instructions in nmi_panic using
      next_insn_same_func. Once it reaches the end of nmi_panic at 0x534 it
      jumps to 0x528 as that's the start of nmi_panic.cold.7. However, since
      the instructions starting at 0x528 are still associated with nmi_panic
      objtool will get stuck in a loop, continually jumping back to 0x528
      after reaching 0x534."
    
    Fix it by shortening the length of the parent function so that the
    functions no longer overlap.
    Reported-and-analyzed-by: default avatarAllan Xavier <allan.x.xavier@oracle.com>
    Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
    Cc: Allan Xavier <allan.x.xavier@oracle.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    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: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/9e704c52bee651129b036be14feda317ae5606ae.1530136978.git.jpoimboe@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarSasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    0bcba956