Messages in this thread | | | Date | Mon, 23 Nov 2015 09:36:44 -0800 | Subject | Re: [PATCH] perf: Fallback to JIT support for mmap'd non-ELF binaries. | From | Stephane Eranian <> |
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On Fri, Nov 20, 2015 at 1:18 PM, Brian Robbins <brianrob@microsoft.com> wrote: > > > On Fri, 20 Nov 2015, Peter Zijlstra wrote: > >> On Thu, Nov 19, 2015 at 11:45:45PM +0000, Brian Robbins wrote: >> >> > Thank you for the feedback. The file format is similar to PE, but is >> > not identical. So, we would be implementing something very scoped, >> > which doesn't feel right to me. >> >> *groan* you just had to go and invent yet another executable format, >> right? :-) > Nah, it just has some extra stuff in it that makes this less desirable - > it's technically PE, but anyway. >> >> > I am interested in the new JIT support, however my understanding from >> > the information that I've read is that it requires kernel support in >> > 4.x, though I can't seem to find where I read that. I want to make >> > sure that this works on older kernels (3.x) as well. >> >> As I think Stephane explained, this is only required if you need to >> match up kernel and userspace timestamps, which is important for dynamic >> code generation, less so for static code in a weird format. > > Yes, agreed. > >> >> So what the new JIT stuff does is online write 'fake' ELF files with >> symbol sections and (optionally?) dwarf debug info for line numbers. >> The debug info section is optional and contains the line table info. This can be used should you want to display source code along with assembly.
>> Since you don't dynamically generate code, you can offline generate >> these ELF files and redirect the symbol parser bits to that (we already >> look for debug ELF files in various locations), or... >> >> > The reason I went with this approach is because it is simple for >> > runtimes to implement and has no requirement that perf understand the >> > file format. I am open to feedback if there is a preferred solution >> > that would still work for older kernels as well. >> >> Since, someone somewhere needs to go parse this funny new file format >> anyhow to either generate /tmp files or fake ELF files or whatever, you >> might as well put that decoder in perf? >> If you have a new binary format, I think you'd have to write the parser in perf.
>> Or just ship these fake ELF files in /usr/lib/debug/ or whatever the >> 'right' location for the distro at hand is. >> > > This seems like a reasonable approach. > > Stephane, are your changes available for public consumption? Last I > recall, the patches were still in review. > I will post V8 this week.
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