• Arnd Bergmann's avatar
    bug.h: work around GCC PR82365 in BUG() · 305eb32d
    Arnd Bergmann authored
    [ Upstream commit 173a3efd ]
    
    Looking at functions with large stack frames across all architectures
    led me discovering that BUG() suffers from the same problem as
    fortify_panic(), which I've added a workaround for already.
    
    In short, variables that go out of scope by calling a noreturn function
    or __builtin_unreachable() keep using stack space in functions
    afterwards.
    
    A workaround that was identified is to insert an empty assembler
    statement just before calling the function that doesn't return.  I'm
    adding a macro "barrier_before_unreachable()" to document this, and
    insert calls to that in all instances of BUG() that currently suffer
    from this problem.
    
    The files that saw the largest change from this had these frame sizes
    before, and much less with my patch:
    
      fs/ext4/inode.c:82:1: warning: the frame size of 1672 bytes is larger than 800 bytes [-Wframe-larger-than=]
      fs/ext4/namei.c:434:1: warning: the frame size of 904 bytes is larger than 800 bytes [-Wframe-larger-than=]
      fs/ext4/super.c:2279:1: warning: the frame size of 1160 bytes is larger than 800 bytes [-Wframe-larger-than=]
      fs/ext4/xattr.c:146:1: warning: the frame size of 1168 bytes is larger than 800 bytes [-Wframe-larger-than=]
      fs/f2fs/inode.c:152:1: warning: the frame size of 1424 bytes is larger than 800 bytes [-Wframe-larger-than=]
      net/netfilter/ipvs/ip_vs_core.c:1195:1: warning: the frame size of 1068 bytes is larger than 800 bytes [-Wframe-larger-than=]
      net/netfilter/ipvs/ip_vs_core.c:395:1: warning: the frame size of 1084 bytes is larger than 800 bytes [-Wframe-larger-than=]
      net/netfilter/ipvs/ip_vs_ftp.c:298:1: warning: the frame size of 928 bytes is larger than 800 bytes [-Wframe-larger-than=]
      net/netfilter/ipvs/ip_vs_ftp.c:418:1: warning: the frame size of 908 bytes is larger than 800 bytes [-Wframe-larger-than=]
      net/netfilter/ipvs/ip_vs_lblcr.c:718:1: warning: the frame size of 960 bytes is larger than 800 bytes [-Wframe-larger-than=]
      drivers/net/xen-netback/netback.c:1500:1: warning: the frame size of 1088 bytes is larger than 800 bytes [-Wframe-larger-than=]
    
    In case of ARC and CRIS, it turns out that the BUG() implementation
    actually does return (or at least the compiler thinks it does),
    resulting in lots of warnings about uninitialized variable use and
    leaving noreturn functions, such as:
    
      block/cfq-iosched.c: In function 'cfq_async_queue_prio':
      block/cfq-iosched.c:3804:1: error: control reaches end of non-void function [-Werror=return-type]
      include/linux/dmaengine.h: In function 'dma_maxpq':
      include/linux/dmaengine.h:1123:1: error: control reaches end of non-void function [-Werror=return-type]
    
    This makes them call __builtin_trap() instead, which should normally
    dump the stack and kill the current process, like some of the other
    architectures already do.
    
    I tried adding barrier_before_unreachable() to panic() and
    fortify_panic() as well, but that had very little effect, so I'm not
    submitting that patch.
    
    Vineet said:
    
    : For ARC, it is double win.
    :
    : 1. Fixes 3 -Wreturn-type warnings
    :
    : | ../net/core/ethtool.c:311:1: warning: control reaches end of non-void function
    : [-Wreturn-type]
    : | ../kernel/sched/core.c:3246:1: warning: control reaches end of non-void function
    : [-Wreturn-type]
    : | ../include/linux/sunrpc/svc_xprt.h:180:1: warning: control reaches end of
    : non-void function [-Wreturn-type]
    :
    : 2.  bloat-o-meter reports code size improvements as gcc elides the
    :    generated code for stack return.
    
    Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
    Link: http://lkml.kernel.org/r/20171219114112.939391-1-arnd@arndb.deSigned-off-by: 's avatarArnd Bergmann <arnd@arndb.de>
    Acked-by: Vineet Gupta <vgupta@synopsys.com>	[arch/arc]
    Tested-by: Vineet Gupta <vgupta@synopsys.com>	[arch/arc]
    Cc: Mikael Starvik <starvik@axis.com>
    Cc: Jesper Nilsson <jesper.nilsson@axis.com>
    Cc: Tony Luck <tony.luck@intel.com>
    Cc: Fenghua Yu <fenghua.yu@intel.com>
    Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: Christopher Li <sparse@chrisli.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: 's avatarSasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    305eb32d
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