Will do, thanks! On Sat, Jun 1, 2019, 3:50 PM Mark Hatle, <mark.ha...@windriver.com> wrote:
> Thanks, this shows that the prelinking is still working in this case. > I'll get > you patch queued up. If you don't see any progress on it this coming week, > please feel free to remind me. > > --Mark > > On 5/29/19 1:42 PM, Shane Peelar wrote: > > Hi Mark, > > > > Thank you for your reply and no problem -- I chose to benchmark ssh-add > with > > it. It contains no `.plt`. > > > > The results are as follows: > > > > Without prelink (ran prelink -auv): > > > > 26019: > > 26019: runtime linker statistics: > > 26019: total startup time in dynamic loader: 1321674 cycles > > 26019: time needed for relocation: 797948 cycles > (60.3%) > > 26019: number of relocations: 624 > > 26019: number of relocations from cache: 3 > > 26019: number of relative relocations: 9691 > > 26019: time needed to load objects: 389972 cycles > (29.5%) > > Could not open a connection to your authentication agent. > > 26019: > > 26019: runtime linker statistics: > > 26019: final number of relocations: 630 > > 26019: final number of relocations from cache: 3 > > > > With prelink (ran prelink -av): > > > > 1930: > > 1930: runtime linker statistics: > > 1930: total startup time in dynamic loader: 462288 cycles > > 1930: time needed for relocation: 48730 cycles > (10.5%) > > 1930: number of relocations: 7 > > 1930: number of relocations from cache: 134 > > 1930: number of relative relocations: 0 > > 1930: time needed to load objects: 286076 cycles > (61.8%) > > Could not open a connection to your authentication agent. > > 1930: > > 1930: runtime linker statistics: > > 1930: final number of relocations: 9 > > 1930: final number of relocations from cache: 134 > > > > I also tested against execstack, which for sure had the assertion fire > on. > > Without prelink: > > > > 27736: > > 27736: runtime linker statistics: > > 27736: total startup time in dynamic loader: 1955954 cycles > > 27736: time needed for relocation: 755440 cycles > (38.6%) > > 27736: number of relocations: 247 > > 27736: number of relocations from cache: 3 > > 27736: number of relative relocations: 1353 > > 27736: time needed to load objects: 710384 cycles > (36.3%) > > /usr/bin/execstack: no files given > > 27736: > > 27736: runtime linker statistics: > > 27736: final number of relocations: 251 > > 27736: final number of relocations from cache: 3 > > > > With prelink: > > > > 3268: > > 3268: runtime linker statistics: > > 3268: total startup time in dynamic loader: 1421206 cycles > > 3268: time needed for relocation: 199396 cycles > (14.0%) > > 3268: number of relocations: 3 > > 3268: number of relocations from cache: 88 > > 3268: number of relative relocations: 0 > > 3268: time needed to load objects: 696886 cycles > (49.0%) > > /usr/bin/execstack: no files given > > 3268: > > 3268: runtime linker statistics: > > 3268: final number of relocations: 5 > > 3268: final number of relocations from cache: 88 > > > > So, it looks like prelink is working on these :) > > > > On Tue, May 28, 2019 at 2:57 PM Mark Hatle <mark.ha...@windriver.com > > <mailto:mark.ha...@windriver.com>> wrote: > > > > Sorry for my delayed reply. I was out on a business trip. > > > > Did you try this with the ld.so statistics to see if the relocations > were indeed > > reduced at runtime? > > > > One of my worries with these changes (since I am not an ELF expert > either) is > > that we make a change that doesn't actually do anything -- but > people expect > > it to. > > > > $ LD_DEBUG=help /lib/ld-linux.so.2 > > Valid options for the LD_DEBUG environment variable are: > > > > libs display library search paths > > reloc display relocation processing > > files display progress for input file > > symbols display symbol table processing > > bindings display information about symbol binding > > versions display version dependencies > > scopes display scope information > > all all previous options combined > > statistics display relocation statistics > > unused determined unused DSOs > > help display this help message and exit > > > > To direct the debugging output into a file instead of standard output > > a filename can be specified using the LD_DEBUG_OUTPUT environment > variable. > > > > I believe that it's the 'statistics' option. > > > > LD_DEBUG=statistics <executable that's been prelinked> > > > > Should result in something like: > > > > 128820: runtime linker statistics: > > 128820: total startup time in dynamic loader: 1974661 > cycles > > 128820: time needed for relocation: 354639 > cycles (17.9%) > > 128820: number of relocations: 90 > > 128820: number of relocations from cache: 3 > > 128820: number of relative relocations: 1201 > > 128820: time needed to load objects: 1303654 > cycles (66.0%) > > 128820: > > 128820: runtime linker statistics: > > 128820: final number of relocations: 94 > > 128820: final number of relocations from cache: 3 > > > > If prelink is working, the number of relocations (relative or > otherwise) will be > > significantly reduced from the original non-relocated version. > > > > If you can run this test, it would give me the assurance that the > patch is safe, > > and I'll get it incorporated into the prelink-cross sources. > > > > --Mark > > > > On 5/25/19 2:53 PM, Shane Peelar wrote: > > > Patch is attached. Thank you! > > > > > > On Sat, May 25, 2019 at 2:30 AM Khem Raj <raj.k...@gmail.com > > <mailto:raj.k...@gmail.com> > > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>>> wrote: > > > > > > On Fri, May 24, 2019 at 6:58 PM Shane Peelar > > <lookatyouhac...@gmail.com <mailto:lookatyouhac...@gmail.com> > > > <mailto:lookatyouhac...@gmail.com <mailto: > lookatyouhac...@gmail.com>>> > > wrote: > > > > > > > > Great! Would you be willing to accept a patch that makes > arch-x86_64.c > > > handle that condition like the other arches? > > > > > > > > > > yes certainly. > > > > > > > -Shane > > > > > > > > On Fri, May 24, 2019 at 12:27 PM Khem Raj < > raj.k...@gmail.com > > <mailto:raj.k...@gmail.com> > > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>>> > wrote: > > > >> > > > >> > > > >> > > > >> On 5/24/19 8:10 AM, Shane Peelar wrote: > > > >> > I did some reading into the sources in other > architectures. The > > closest > > > >> > match, arch_i386.c, makes the write conditional as you > say. > > > >> > So do other arches, including |arch_arm.c, |arch_sh.c, > |arch-mips.c, > > > >> > |arch-s390.c, |arch-s390x.c, and |arch-ia64.c.|||||| > > > >> > |||||| > > > >> > |||||| > > > >> > Notably, |||||||arch-cris.c||||||| has the same assert as > > > >> > |||||||arch-x86_64.c||||||| instead of the conditional. > > > >> > > > > >> > The code roughly looks like follows:|||||||||||||| > > > >> > |||||||||||||| > > > >> > ||||||| > > > >> > ||||||| > > > >> > 1. Check for dso->info[DT_PLTGOT]. If it does not exist, > return 0 > > > >> > 2. Call addr_to_sec on dso->info[DT_PLTGOT], return 1 if > error > > > >> > 3. Look for the section named ".plt" in the ELF. > > > >> > 4. If the section cannot be found, return 0 > > > >> > 5. Otherwise, write the address of .plt + constant > (dependent on > > arch) > > > >> > to got[1]|||||||||||||| > > > >> > |||||||||||||| > > > >> > ||||||| > > > >> > ||||||| > > > >> > In |||||||arch-x86_64.c and arch-cris.c|||||||, step (4) > above is an > > > >> > assert:||||||| > > > >> > > > > >> > |||||||1. Check for dso->info[DT_PLTGOT]. If it does not > exist, > > return 0 > > > >> > 2. Call addr_to_sec on dso->info[DT_PLTGOT], return 1 if > error > > > >> > 3. Look for the section named ".plt" in the ELF. > > > >> > 4. Assert that the section was found > > > >> > 5. Write the address of .plt + constant (dependent on > arch) to got[1] > > > >> > > > > >> > I tested out making the assert conditional and nothing > seemed to > > break > > > >> > at least. > > > >> > ||||||| > > > >> > ||||||| > > > >> > > > >> It seems ok to me. > > > >> > > > >> > > > > >> > On Fri, May 24, 2019 at 12:08 AM Khem Raj < > raj.k...@gmail.com > > <mailto:raj.k...@gmail.com> > > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>> > > > >> > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com> > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>>>> wrote: > > > >> > > > > >> > > > > >> > > > > >> > On 5/23/19 7:53 PM, Shane Peelar wrote: > > > >> > > Any of them on the system pretty much, and yes > they are also > > > >> > built with > > > >> > > -fno-plt. > > > >> > > > > >> > OK, I think its better to them conditionally check > for .plt > > section, > > > >> > can you describe more of whats going on when sections > are > > checked. > > > >> > > > > >> > > > > > >> > > On Thu, May 23, 2019 at 9:59 PM Khem Raj > > <raj.k...@gmail.com <mailto:raj.k...@gmail.com> > > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>> > > > >> > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com > > > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>>> > > > >> > > <mailto:raj.k...@gmail.com <mailto: > raj.k...@gmail.com> > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>> > > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com> > > <mailto:raj.k...@gmail.com <mailto:raj.k...@gmail.com>>>>> wrote: > > > >> > > > > > >> > > > > > >> > > > > > >> > > On 5/23/19 8:05 AM, Shane Peelar wrote: > > > >> > > > Hi Everyone @ the Yocto project, > > > >> > > > > > > >> > > > I'm Shane Peelar, a PhD Candidate at the > University of > > > >> > Windsor. > > > >> > > > I'm writing to you about prelink-cross, as > part of the > > > >> > Yocto project. > > > >> > > > Specifically, I'm looking at using it with > executables > > > >> > built using > > > >> > > > `-fno-plt` under GCC. > > > >> > > > I wasn't quite sure where to send this > email to, so I > > > >> > figured I'd > > > >> > > try > > > >> > > > here. If there's a better place to send > this, > > please let > > > >> > me know. > > > >> > > > > > > >> > > > Right now, prelink-cross seems to fail an > assertion in > > > >> > > arch-x86_64.c, > > > >> > > > line 421, when > > > >> > > > using it with an executable built with > `-fno-plt`: > > > >> > > > > > > >> > > > ... > > > >> > > > assert (i < dso->ehdr.e_shnum) > > > >> > > > ... > > > >> > > > > > > >> > > > This snippet seems to be looking for the > ".plt" > > section and, > > > >> > > since it > > > >> > > > can't find it, the assertion fires. This > makes sense > > > >> > because in > > > >> > > > `-fno-plt` executables, the `.plt` section > is missing > > > >> > entirely. > > > >> > > > I'm not an expert on ELF stuff, although I > am learning > > > >> > quickly. It > > > >> > > > looks like > > > >> > > > this code wants to write into GOT[1] the > address of > > ".plt" > > > >> > + 0x16 -- > > > >> > > > since ".plt" doesn't > > > >> > > > exist, does it make sense to just change > this > > assert to an if > > > >> > > statement > > > >> > > > like so: > > > >> > > > > > > >> > > > ... > > > >> > > > if (i < dso->ehdr.e_shnum) > > > >> > > > { ... } > > > >> > > > ... > > > >> > > > > > > >> > > > and skip over that part? Or is this a real > error > > > >> > condition for > > > >> > > > prelink-cross and it really should not > continue? The > > > >> > executable in > > > >> > > > question is also non-PIE, if that makes a > difference. > > > >> > > > > > > >> > > > > > >> > > what shared libs is this linking to ? are they > also > > built with > > > >> > > -fno-plt ? > > > >> > > > > > >> > > > Thanks for your time, > > > >> > > > Shane > > > >> > > > > > > >> > > > > > >> > > > > > > > > > > >
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