Messages in this thread |  | | | Date | Wed, 27 Jan 2010 02:43:39 -0800 (PST) | | From | Linus Torvalds <> | | Subject | Re: linux-next: add utrace tree |
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On Wed, 27 Jan 2010, Peter Zijlstra wrote: > > Right, so you're going to love uprobes, which does exactly that. The > current proposal is overwriting the target instruction with an INT3 and > injecting an extra vma into the target process's address space > containing the original instruction(s) and possible jumps back to the > old code stream.
Just out of interest, how does it handle the threading issue?
Last I saw, at least some CPU people were _very_ nervous about overwriting instructions if another CPU might be just about to execute them.
Even the "overwrite only the first byte with 'int3'" made them go "umm, I need to talk to some core CPU people to see if that's ok". They mumble about possible CPU errata, I$ coherency, instruction retry etc.
I realize kprobes does this very thing, but kprobes is esoteric stuff and doesn't have much choice. In user space, you _could_ do the modification on a different physical page and then just switch the page table entry instead, and not get into the whole D$/I$ coherency thing at all.
Linus
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