Messages in this thread | | | Date | Fri, 20 Nov 2015 13:18:55 -0800 (PST) | From | Brian Robbins <> | Subject | Re: [PATCH] perf: Fallback to JIT support for mmap'd non-ELF binaries. |
| |
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. > > 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? > > 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.
Thanks. -Brian
| |