tracing: Add alignment to syscall metadata declarations
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From: Steven Rostedt on 9 Jul 2010 16:50 On Fri, 2010-07-09 at 22:33 +0200, Sam Ravnborg wrote: > On Fri, Jul 09, 2010 at 03:56:42PM -0400, Steven Rostedt wrote: > This looks like a fix that just hide the real bug. > If I remember the original report correct the problem is > that the symbol: > > __start_syscalls_metadata > > Does not point to a valid syscall entry. > > The symbol is assigned in vmlinux.lds.h like this: > #define TRACE_SYSCALLS() VMLINUX_SYMBOL(__start_syscalls_metadata) = .; \ > *(__syscalls_metadata) \ > VMLINUX_SYMBOL(__stop_syscalls_metadata) = .; > > Now consider what is happening if we have the following scanario: > > . equals 0x1004 so __start_syscalls_metadata is set to 0x1004 > But __syscall_metadata require 8 byte alignment so it starts at 0x1008. I did not know that the linker could start a section at a half a word size. That seems to me to be a linker bug. If a word for a box is 8 bytes than the linker had better start sections on 8 byte boundaries. Otherwise I would think other things may break. For 4 byte word boxes, this should be safe anyway. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Steven Rostedt on 9 Jul 2010 17:10 On Fri, 2010-07-09 at 22:53 +0200, Sam Ravnborg wrote: > But in this case we have no control of the value of "." (current address) > when we have processed (_ftrace_events) so it may even be at a 2 byte boundary. > The linker will add padding as needed to satisfy the alignmnet of > __syscalls_metadata - but that padding will be inbetween "." and the first > member in __syscalls_metadata. Fine, but this is a separate issue. I doubt the "ALIGN(8);" would have helped us anyway. Remember what the issue we had: ffffffff8173c438 <__start_syscalls_metadata>: ... ffffffff8173c440 <__syscall_meta__mmap>: __start_syscalls_metadata was already aligned to 8, but for some strange reason, gcc decided to align the first member to 16. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Steven Rostedt on 9 Jul 2010 20:30
On Fri, 2010-07-09 at 14:25 -0700, Linus Torvalds wrote: > On Fri, Jul 9, 2010 at 1:33 PM, Sam Ravnborg <sam(a)ravnborg.org> wrote: > > > > Something like this: > > (whitespace damaged) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index 48c5299..64430d3 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -133,7 +133,8 @@ > > #endif > > > > #ifdef CONFIG_FTRACE_SYSCALLS > > -#define TRACE_SYSCALLS() VMLINUX_SYMBOL(__start_syscalls_metadata) = .; \ > > +#define TRACE_SYSCALLS() . = ALIGN(8); \ > > + VMLINUX_SYMBOL(__start_syscalls_metadata) = .; \ > > *(__syscalls_metadata) \ > > VMLINUX_SYMBOL(__stop_syscalls_metadata) = .; > > #else > > If this is confirmed to fix it, then I would much prefer this version. Zeev, Can you try Sam's version and remove mine. I'd like to see if that fixes the issue too. Thanks, -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |