Messages in this thread Patch in this message | | | Date | Fri, 10 Feb 2006 21:06:23 -0500 (EST) | From | "Albert D. Cahalan" <> | Subject | [PATCH] document sysenter path |
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This path isn't obvious. It looks as if the kernel will be taking three args from the user stack, but it only takes one from there.
Signed-off-by: Albert Cahalan <acahalan@gmail.com>
diff -Naurd old/arch/i386/kernel/vsyscall-sysenter.S new/arch/i386/kernel/vsyscall-sysenter.S --- old/arch/i386/kernel/vsyscall-sysenter.S 2006-02-10 19:55:27.000000000 -0500 +++ new/arch/i386/kernel/vsyscall-sysenter.S 2006-02-10 20:29:39.000000000 -0500 @@ -7,6 +7,21 @@ * for details. */ +/* + * The caller puts arg2 in %ecx, which gets pushed. The kernel will use + * %ecx itself for arg2. The pushing is because the sysexit instruction + * (found in entry.S) requires that we clobber %ecx with the desired %esp. + * User code might expect that %ecx is unclobbered though, as it would be + * for returning via the iret instruction, so we must push and pop. + * + * The caller puts arg3 in %edx, which the sysexit instruction requires + * for %eip. Thus, exactly as for arg2, we must push and pop. + * + * Arg6 is different. The caller puts arg6 in %ebp. Since the sysenter + * instruction clobbers %esp, the user's %esp won't even survive entry + * into the kernel. We store %esp in %ebp. Code in entry.S must fetch + * arg6 from the stack. + */ .text .globl __kernel_vsyscall .type __kernel_vsyscall,@function - 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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