[CRIU] Error (pie-util-vdso.c:190): vdso: Not all dynamic entries are present

[Tycho Andersen]

Hi Dmitry,

On Tue, Jun 07, 2016 at 06:36:49PM +0300, Dmitry Safonov wrote:
> >Ok, I fetched your kernel.
> >Here is it:
> >[ubuntu-unstable]$ git checkout 66b7a6c3fa35ea617c60d938bd2028eb6141c2f0
> >[ubuntu-unstable]$ make clean
> >...
> >[ubuntu-unstable]$ make -j5 arch/x86/entry/vdso/
> >...
> >[ubuntu-unstable]$ readelf --program-headers arch/x86/entry/vdso/vdso64.so
> >
> >Elf file type is EXEC (Executable file)
> >Entry point 0x5c0
> >There are 4 program headers, starting at offset 64
> >
> >Program Headers:
> >  Type           Offset             VirtAddr           PhysAddr
> >                 FileSiz            MemSiz              Flags  Align
> >  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
> >                 0x0000000000000979 0x0000000000000979  R E    1000
> >  DYNAMIC        0x0000000000000000 0x0000000000000000 0x0000000000000000
> >                 0x0000000000000000 0x0000000000000000  R      8
> >readelf: Error: no .dynamic section in the dynamic segment
> >  NOTE           0x0000000000000460 0x0000000000000460 0x0000000000000460
> >                 0x000000000000003c 0x000000000000003c  R      4
> >  GNU_EH_FRAME   0x000000000000049c 0x000000000000049c 0x000000000000049c
> >                 0x0000000000000034 0x0000000000000034  R      4
> >
> > Section to Segment mapping:
> >  Segment Sections...
> >   00     .rodata .note .eh_frame_hdr .eh_frame .text .altinstructions
> >.altinstr_replacement
> >   01
> >   02     .note
> >   03     .eh_frame_hdr
> >
> >
> >See? There is no .dynamic section :)
> >
> >Ok, lets find, what broke it...
> >[ubuntu-unstable]$ git checkout f8830b2956a3~1
> >[ubuntu-unstable]$ make clean
> >...
> >[ubuntu-unstable]$ make -j5 arch/x86/entry/vdso/
> >...
> >[ubuntu-unstable]$ readelf --program-headers arch/x86/entry/vdso/vdso64.so
> >
> >Elf file type is DYN (Shared object file)
> >Entry point 0x910
> >There are 4 program headers, starting at offset 64
> >
> >Program Headers:
> >  Type           Offset             VirtAddr           PhysAddr
> >                 FileSiz            MemSiz              Flags  Align
> >  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
> >                 0x0000000000000cb9 0x0000000000000cb9  R E    1000
> >  DYNAMIC        0x0000000000000360 0x0000000000000360 0x0000000000000360
> >                 0x0000000000000110 0x0000000000000110  R      8
> >  NOTE           0x00000000000007b0 0x00000000000007b0 0x00000000000007b0
> >                 0x000000000000003c 0x000000000000003c  R      4
> >  GNU_EH_FRAME   0x00000000000007ec 0x00000000000007ec 0x00000000000007ec
> >                 0x0000000000000034 0x0000000000000034  R      4
> >
> > Section to Segment mapping:
> >  Segment Sections...
> >   00     .hash .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_d
> >.dynamic .rodata .note .eh_frame_hdr .eh_frame .text .altinstructions
> >.altinstr_replacement
> >   01     .dynamic
> >   02     .note
> >   03     .eh_frame_hdr
> >
> >
> >And here it is. Not sure that this commit f8830b2956a3 ("disable -pie
> >when gcc has it enabled by default") has broke it, but it looks quite
> >suspicious.
> >
> >Anyway, I'm not sure, maybe we could re-arrange vdso code in CRIU
> >that it wouldn't need .dynamic? I'm not sure, maybe I'll check it
> >when I'll have some more time :)
> 
> But it's very unclear, what can we do if there is no .dynamic
> We really need symbols and their location information.
> So, vDSO looks quite useless without it. I'm surprised that
> your glibc works with that (is it?). Maybe it fails back to raw
> syscall instructions instead of fast syscalls - I don't know
> if you have check that after that patch.

Thanks for the analysis. I just tested, and sure enough it does fall
back to real syscalls, so that seems like a big problem :)

I'll check with our kernel guys and see, but based on looking at the
code we do need the .dynamic section so we can reposition things.

Tycho