Re: [yocto] prelink-cross with -fno-plt

[Shane Peelar]

Will do, thanks!

On Sat, Jun 1, 2019, 3:50 PM Mark Hatle,  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  > > 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:
> >
> >   libsdisplay library search paths
> >   reloc   display relocation processing
> >   files   display progress for input file
> >   symbols display symbol table processing
> >   bindingsdisplay information about symbol binding
> >   versionsdisplay version dependencies
> >   scopes  display scope information
> >   all all previous options combined
> >   statistics  display relocation statistics
> >   unused  determined unused DSOs
> >   helpdisplay this help message and exit
> >
> > To direct the debugging output into a file instead of standard output
> > a filename can be 

Re: [yocto] prelink-cross with -fno-plt

[Mark Hatle]

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  > 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 
> 
> Should result in something like:
> 
>     128820:     runtime linker statistics:
>     128820:       total startup time in 

Re: [yocto] prelink-cross with -fno-plt

[Shane Peelar]

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  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:
>
>   libsdisplay library search paths
>   reloc   display relocation processing
>   files   display progress for input file
>   symbols display symbol table processing
>   bindingsdisplay information about symbol binding
>   versionsdisplay version dependencies
>   scopes  display scope information
>   all all previous options combined
>   statistics  display relocation statistics
>   unused  determined unused DSOs
>   helpdisplay 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 
>
> 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 

Re: [yocto] prelink-cross with -fno-plt

[Mark Hatle]

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:

  libsdisplay library search paths
  reloc   display relocation processing
  files   display progress for input file
  symbols display symbol table processing
  bindingsdisplay information about symbol binding
  versionsdisplay version dependencies
  scopes  display scope information
  all all previous options combined
  statistics  display relocation statistics
  unused  determined unused DSOs
  helpdisplay 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 

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  > wrote:
> 
> On Fri, May 24, 2019 at 6:58 PM Shane Peelar  > 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  > 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  
> >> > >> 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 
> 

Re: [yocto] prelink-cross with -fno-plt

[Shane Peelar]

Patch is attached.  Thank you!

On Sat, May 25, 2019 at 2:30 AM Khem Raj  wrote:

> On Fri, May 24, 2019 at 6:58 PM Shane Peelar 
> 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  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  >> > > 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  >> > 
> >> >  > >>
> 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 

Re: [yocto] prelink-cross with -fno-plt

[Khem Raj]

On Fri, May 24, 2019 at 6:58 PM Shane Peelar  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  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 > > > 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 > > 
>> >  > >> 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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Re: [yocto] prelink-cross with -fno-plt

[Shane Peelar]

Great!  Would you be willing to accept a patch that makes arch-x86_64.c
handle that condition like the other arches?

-Shane

On Fri, May 24, 2019 at 12:27 PM Khem Raj  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  > > 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  > 
> >  > >> 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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Re: [yocto] prelink-cross with -fno-plt

[Khem Raj]

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 > 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 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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Re: [yocto] prelink-cross with -fno-plt

[Shane Peelar]

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.


On Fri, May 24, 2019 at 12:08 AM Khem Raj  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  > > 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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Re: [yocto] prelink-cross with -fno-plt

[Khem Raj]

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 > 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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Re: [yocto] prelink-cross with -fno-plt

[Shane Peelar]

Any of them on the system pretty much, and yes they are also built with
-fno-plt.

On Thu, May 23, 2019 at 9:59 PM Khem Raj  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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Re: [yocto] prelink-cross with -fno-plt

[Khem Raj]

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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[yocto] prelink-cross with -fno-plt

[Shane Peelar]

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.

Thanks for your time,
Shane
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