Messages in this thread Patch in this message | | | Date | 15 Jan 2004 08:48:34 +0100 | Date | Thu, 15 Jan 2004 08:48:34 +0100 | From | Andi Kleen <> | Subject | Re: [PATCH] Add noinline attribute |
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On Wed, Jan 14, 2004 at 03:23:35PM -0800, Linus Torvalds wrote: > > > On Wed, 14 Jan 2004, Andi Kleen wrote: > > > > do_test_wp_bit cannot be inlined, otherwise the kernel doesn't boot > > because the exception tables get reordered. > > This patch seems to just hide the _real_ bug, which is that the exception > table gets confused. > > If the exception table is confused, you'll get oopses on bad user system > call pointers, but since that is uncommon, you'll never see it under > normal circumstances. This is the only exception that you'll always see.
Actually you would get a non booting system because the broken mount ABI does a stress test of EFAULT on every boot.
The only problem is using the exception table from __init functions. It is long known that this doesn't work because the exception table setup relies on the linker generating functions in order and __init violates that.
This has broken various things over time, but so far nothing in mainline i386 yet. I think kdb did this sorting forever for example.
> So it sounds like you have a compiler combination that breaks the > exception table totally for _any_ function called from any non-regular > segment, and this just happens to be the only one you actually saw. > > How about just fixing the exception table instead? A bogo-sort at boot > time?
That's fine for me. In fact I did this some time ago on x86-64 when I ran into similar problems. Here's a port of the x86-64 sort function.
-AndI
diff -u linux-34/arch/i386/mm/extable.c-o linux-34/arch/i386/mm/extable.c --- linux-34/arch/i386/mm/extable.c-o 2003-05-27 03:01:00.000000000 +0200 +++ linux-34/arch/i386/mm/extable.c 2004-01-15 08:39:31.657013864 +0100 @@ -5,6 +5,7 @@ #include <linux/config.h> #include <linux/module.h> #include <linux/spinlock.h> +#include <linux/init.h> #include <asm/uaccess.h> /* Simple binary search */ @@ -56,3 +57,28 @@ return 0; } + +/* When an exception handler is in an non standard section (like __init) + the fixup table can end up unordered. Fix that here. */ +__init int check_extable(void) +{ + extern struct exception_table_entry __start___ex_table[]; + extern struct exception_table_entry __stop___ex_table[]; + struct exception_table_entry *e; + int change; + + /* The input is near completely presorted, which makes bubble sort the + best (and simplest) sort algorithm. */ + do { + change = 0; + for (e = __start___ex_table+1; e < __stop___ex_table; e++) { + if (e->insn < e[-1].insn) { + struct exception_table_entry tmp = e[-1]; + e[-1] = e[0]; + e[0] = tmp; + change = 1; + } + } + } while (change != 0); + return 0; +} diff -u linux-34/arch/i386/kernel/setup.c-o linux-34/arch/i386/kernel/setup.c --- linux-34/arch/i386/kernel/setup.c-o 2004-01-09 09:27:09.000000000 +0100 +++ linux-34/arch/i386/kernel/setup.c 2004-01-15 08:39:30.438199152 +0100 @@ -119,6 +119,7 @@ extern void generic_apic_probe(char *); extern int root_mountflags; extern char _end[]; +extern int check_extable(void); unsigned long saved_videomode; @@ -1114,6 +1115,8 @@ #endif paging_init(); + check_extable(); + dmi_scan_machine(); #ifdef CONFIG_X86_GENERICARCH - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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