Messages in this thread |  | | Date | Wed, 4 Dec 2013 09:15:04 -0800 | Subject | Re: [PATCH?] uprobes: change uprobe_write_opcode() to modify the page directly | From | Linus Torvalds <> |
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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.
Linus
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