Hi Mike, Thanks for following up on this. On 12/31/13 20:32, Mike Frysinger wrote: > On Wednesday 22 May 2013 09:22:09 Michael Kerrisk wrote: >> On 04/12/13 03:28, Mike Frysinger wrote: >>> here's v2 w/Andy's feedback >> >> Thanks for this--it's a nice piece of work. Could you take a >> look at my comments below and send a v3, please. > > anything i didn't explicitly respond to below i merged with my version > >>> the kernel you wish to make a syscall. >>> However, this instruction is expensive: it goes through the full >>> interrupt handling paths in the processor's microcode as well as in the >>> kernel. Newer processors have faster (but backwards incompatible) >>> instructions to initiate system calls. >>> Rather than require the C library to figure out if this functionality is >>> available at runtime itself, it can use functions provided by the kernel >>> in the vDSO. >> >> That last point (after the comma) is the most interesting (IMO) of the use >> cases of the vDSO. If you cared to expand on the details (i.e., are what >> are mechanics of the operation of those functions provided by the kernel), >> I think that would be interesting for the reader. > > i think the paragraph after this explains things somewhat as you'd like (where > it talks about gettimeofday) ? Yes, thanks. >>> All symbols are also versioned (using the GNU version format). >>> This allows the kernel (in the very unlikely situation) to update the >>> function >> >> s/situation/case that it is necessary/ > > hmm, i see what you mean, but i think your version isn't really better ... > just different. i'll just delete the (...) text. Okay. >>> You use the standard C calling conventions when calling any of these >>> functions. No need to worry about weird register or stack behavior. >> >> That last sentence is a little incomplete. Could you expand/reword a little >> please. > > it's meant as a follow up to the previous sentence. so the implication is > that there are no functions which violate the C ABI for your particular > target. arguments get passed in the standard way (registers/stack), and all > the registers have corresponding behavior: scratch are scratch, caller- > preserved are caller-preserved, callee-preserved are callee-preserved, etc... >>> Note that the vDSO that is used is based on the ABI of your userspace >>> code and not the ABI of the kernel. >>> i.e. If you run an i386 32bit ELF under an i386 32bit kernel or under an >> >> s/i.e. If/In other words, if/ > > i.e. shows up a lot in man pages as does e.g. (and both show up in this new > vdso(7) page) ... I should have been clearer. I disfavor the use of "e.g." and "i.e.", except in parenthetical asides. There were a very few exceptions to that guideline, and I just now went through and stamped out most of them. And I edited your page to be consistent with the guideline. >>> So when referring to sections below, use the userspace ABI. >> >> It's not clear what you mean here when you say "use the userspace ABI." >> Could you clarify? > > the two sentences that preceded this one explained things ... Sorry -- I still don't get it... (See my other reply.) Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
