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 -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
