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Message-ID: <87ipf9gtsb.fsf@xmission.com> Date: Sat, 02 Jun 2012 17:48:04 -0600 From: ebiederm@...ssion.com (Eric W. Biederman) To: hacklu <embedway.linux@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: why the decompressed procedure move kernel from address 0x100000(1M) to 0x1000000(16M) +x hacklu <embedway.linux@...il.com> writes: > hi all, > recently, I got some puzzle when I read source code of the system boot. I need > some help. > > at the end of src/arch/x86/boot/header.S, kernel jump to 0x100000(where is the > src/arch/x86/boot/compressed/head_32.S). > in __this__ head_32.S, I found the kernel is move to 0x1000000(mostly is to > here) +x. the x distance is used for decompressed buf. must leave some distance > for decompressing without overlap. > > after the move, kernel is decompressed at 0x1000000(16m). and jump to it. > > so why not decompressed kernel at 0x100000(1M) to 0x1000000(16m) directly > without moving? > > is the move necessary? The move is nececcessary if we are doing the decompression in place. Without a move it is hard to tell if there are going to be overlapping address problems. The move is cheap so there is no apparent reason to optimize it away. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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