Messages in this thread |  | | Date | Wed, 04 Dec 2013 10:32:07 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH?] uprobes: change uprobe_write_opcode() to modify the page directly |
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On 12/04/2013 09:15 AM, Linus Torvalds wrote: > On Wed, Dec 4, 2013 at 8:54 AM, H. Peter Anvin <hpa@zytor.com> wrote: >> >> That is why I talk about the atomic instruction word... most (but not >> *all*) architectures have a fundamental minimum unit of instructions >> which is aligned and can be atomically written. Typically this is 1, 2, >> or 4 bytes. > > Note that it's not just about the "atomically written", it's also > about the guarantee that it's atomically *read*. > > x86 can certainly atomically write a 4-byte instruction too, it's just > that there's no guarantee - even if the instruction is aligned etc - > that the actual instruction decoding always ends up reading it that > way. It might re-read an instruction after encountering a prefix byte > etc etc. So even if it's all properly aligned, the reading side might > do something odd. >
True, at least in theory, but the atomic instruction quantum on x86 is a byte.
-hpa
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