svn commit: r339876 - head/libexec/rtld-elf
Alexander Richardson
arichardson at freebsd.org
Tue Oct 30 22:12:37 UTC 2018
On Tue, 30 Oct 2018 at 21:32, Mark Millard <marklmi26-fbsd at yahoo.com> wrote:
>
>
>
> On 2018-Oct-30, at 2:23 PM, Alexander Richardson <arichardson at freebsd.org> wrote:
>
> > On Tue, 30 Oct 2018 at 18:19, Mark Millard <marklmi26-fbsd at yahoo.com> wrote:
> >>
> >> Alexander Richardson arichardson at freebsd.org wrote on
> >> Tue Oct 30 15:33:00 UTC 2018 :
> >>
> >>> On Tue, 30 Oct 2018 at 10:17, Michael Tuexen
> >>> <Michael.Tuexen at macmic.franken.de> wrote:
> >>>>
> >>>>> On 29. Oct 2018, at 22:08, Alex Richardson <arichardson at FreeBSD.org> wrote:
> >>>>>
> >>>>> Author: arichardson
> >>>>> Date: Mon Oct 29 21:08:02 2018
> >>>>> New Revision: 339876
> >>>>> URL: https://svnweb.freebsd.org/changeset/base/339876
> >>>>>
> >>>>> Log:
> >>>>> rtld: set obj->textsize correctly
> >>>>>
> >>>>> With lld-generated binaries the first PT_LOAD will usually be a read-only
> >>>>> segment unless you pass --no-rosegment. For those binaries the textsize is
> >>>>> determined by the next PT_LOAD. To allow both LLD and bfd 2.17 binaries to
> >>>>> be parsed correctly use the end of the last PT_LOAD that is marked as
> >>>>> executable instead.
> >>>>>
> >>>>> I noticed that the value was wrong while adding some debug prints for some rtld
> >>>>> changes for CHERI binaries. `obj->textsize` only seems to be used by PPC so the
> >>>>> effect is untested. However, the value before was definitely wrong and the new
> >>>>> result matches the phdrs.
> >>>> I build kernel and world with a revision later than this on a PPC. Buildword
> >>>> ends up with a world where almost all binaries are segfaulting.... Especially gdb
> >>>> (but svn, ls or so all segfault).
> >>>>
> >>>> Best regards
> >>>> Michael
> >>>
> >>> This is rather surprising since if anything the range of the icache
> >>> flush should increase rather than decrease after this change.
> >>>
> >>> I can only see this causing a behaviour change if we actually need to
> >>> flush more than just the executable segments.
> >>> Is it possible that some binary/library contains a non-executable
> >>> segment as the first PT_LOAD?
> >>> Or is there some linker script that adds custom PHDRS?
> >>
> >> The following is based on using devel/powerpc64-xtoolchain-gcc
> >> to buildworld buildkernel on/for powerpc64. (I experiment with
> >> using fairly modern tools to target powerpc64 and powerpc.)
> >> The build context is head -r339076 based, both for what
> >> did the build and for what it was building.
> >>
> >> I report from both elfdump and objdump output
> >> because each seems to have some oddities in what
> >> it outputs.
> >>
> >> I start with elfdump (which leaves sh_flags blank
> >> and shows a section header with sh_name empty
> >> that objdump does not list at all):
> >>
> >> # elfdump -pc /bin/ls | less
> >>
> >> . . .
> >>
> >> As for objdump on the same file (section
> >> one less than elfdump listed, no empty sh_name
> >> section listed):
> >>
> >> # objdump -ph /bin/ls | less
> >>
> >> /bin/ls: file format elf64-powerpc-freebsd
> >>
> >> Program Header:
> >> PHDR off 0x0000000000000040 vaddr 0x0000000010000040 paddr 0x0000000010000040 align 2**3
> >> filesz 0x0000000000000188 memsz 0x0000000000000188 flags r--
> >> INTERP off 0x00000000000001c8 vaddr 0x00000000100001c8 paddr 0x00000000100001c8 align 2**0
> >> filesz 0x0000000000000015 memsz 0x0000000000000015 flags r--
> >> LOAD off 0x0000000000000000 vaddr 0x0000000010000000 paddr 0x0000000010000000 align 2**16
> >> filesz 0x000000000000910c memsz 0x000000000000910c flags r-x
> >> LOAD off 0x0000000000009110 vaddr 0x0000000010019110 paddr 0x0000000010019110 align 2**16
> >> filesz 0x0000000000000ee0 memsz 0x00000000000010e8 flags rw-
> >> DYNAMIC off 0x0000000000009138 vaddr 0x0000000010019138 paddr 0x0000000010019138 align 2**3
> >> filesz 0x00000000000001c0 memsz 0x00000000000001c0 flags rw-
> >> NOTE off 0x00000000000001e0 vaddr 0x00000000100001e0 paddr 0x00000000100001e0 align 2**2
> >> filesz 0x0000000000000030 memsz 0x0000000000000030 flags r--
> >> STACK off 0x0000000000000000 vaddr 0x0000000000000000 paddr 0x0000000000000000 align 2**4
> >> filesz 0x0000000000000000 memsz 0x0000000000000000 flags rw-
> >>
> >> Dynamic Section:
> >> NEEDED libutil.so.9
> >> NEEDED libncursesw.so.8
> >> NEEDED libc.so.7
> >> INIT 0x0000000010019328
> >> FINI 0x0000000010019340
> >> HASH 0x0000000010000210
> >> STRTAB 0x0000000010000d00
> >> SYMTAB 0x0000000010000490
> >> STRSZ 0x000000000000035a
> >> SYMENT 0x0000000000000018
> >> DEBUG 0x0000000000000000
> >> PLTGOT 0x0000000010019898
> >> PLTRELSZ 0x00000000000006f0
> >> PLTREL 0x0000000000000007
> >> JMPREL 0x00000000100012f8
> >> 0x70000000 0x00000000100089b4
> >> RELA 0x0000000010001160
> >> RELASZ 0x0000000000000198
> >> RELAENT 0x0000000000000018
> >> VERNEED 0x0000000010001110
> >> VERNEEDNUM 0x0000000000000001
> >> VERSYM 0x000000001000105a
> >>
> >> Version References:
> >> required from libc.so.7:
> >> 0x077a28b3 0x00 05 FBSD_1.3
> >> 0x077a28b1 0x00 04 FBSD_1.1
> >> 0x077a28b5 0x00 03 FBSD_1.5
> >> 0x077a28b0 0x00 02 FBSD_1.0
> >> private flags = 0x1: [abiv1]
> >>
> >> Sections:
> >> Idx Name Size VMA LMA File off Algn
> >> 0 .interp 00000015 00000000100001c8 00000000100001c8 000001c8 2**0
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 1 .note.tag 00000030 00000000100001e0 00000000100001e0 000001e0 2**2
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 2 .hash 0000027c 0000000010000210 0000000010000210 00000210 2**3
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 3 .dynsym 00000870 0000000010000490 0000000010000490 00000490 2**3
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 4 .dynstr 0000035a 0000000010000d00 0000000010000d00 00000d00 2**0
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 5 .gnu.version 000000b4 000000001000105a 000000001000105a 0000105a 2**1
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 6 .gnu.version_r 00000050 0000000010001110 0000000010001110 00001110 2**3
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 7 .rela.dyn 00000198 0000000010001160 0000000010001160 00001160 2**3
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 8 .rela.plt 000006f0 00000000100012f8 00000000100012f8 000012f8 2**3
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 9 .init 0000002c 00000000100019f0 00000000100019f0 000019f0 2**4
> >> CONTENTS, ALLOC, LOAD, READONLY, CODE
> >> 10 .text 00007204 0000000010001a20 0000000010001a20 00001a20 2**5
> >> CONTENTS, ALLOC, LOAD, READONLY, CODE
> >> 11 .fini 00000024 0000000010008c30 0000000010008c30 00008c30 2**4
> >> CONTENTS, ALLOC, LOAD, READONLY, CODE
> >> 12 .rodata 000004b0 0000000010008c58 0000000010008c58 00008c58 2**3
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 13 .eh_frame 00000004 0000000010009108 0000000010009108 00009108 2**2
> >> CONTENTS, ALLOC, LOAD, READONLY, DATA
> >> 14 .ctors 00000010 0000000010019110 0000000010019110 00009110 2**3
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 15 .dtors 00000010 0000000010019120 0000000010019120 00009120 2**3
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 16 .jcr 00000008 0000000010019130 0000000010019130 00009130 2**3
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 17 .dynamic 000001c0 0000000010019138 0000000010019138 00009138 2**3
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 18 .opd 00000468 00000000100192f8 00000000100192f8 000092f8 2**3
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 19 .got 00000098 0000000010019800 0000000010019800 00009800 2**8
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 20 .plt 00000708 0000000010019898 0000000010019898 00009898 2**3
> >> ALLOC
> >> 21 .data 00000050 0000000010019fa0 0000000010019fa0 00009fa0 2**3
> >> CONTENTS, ALLOC, LOAD, DATA
> >> 22 .bss 00000208 0000000010019ff0 0000000010019ff0 00009ff0 2**3
> >> ALLOC
> >> 23 .comment 000002b5 0000000000000000 0000000000000000 00009ff0 2**0
> >> CONTENTS, READONLY
> >> 24 .gnu_debuglink 00000010 0000000000000000 0000000000000000 0000a2a8 2**2
> >> CONTENTS, READONLY
> >>
> >>
> >
> > The first PT_LOAD is also executable so there will be no be behaviour
> > change. It must be one of the library dependencies that is different.
> > The difference in section headers output doesn't matter here since all
> > that RTLD looks at is the PHDRS.
> >
>
> I think you missed the fact that the .got and .plt are in the
> material from the 2nd PT_LOAD: there are writeable code areas
> involved for powerpc64.
>
> So both PT_LOAD's contribute code areas and there is a space
> between the two contributions. The first PT_LOAD loads most
> code (the readonly code, to be specific). The 2nd contributes
> a writable-code area.
>
> But may be i've misunderstood the assumptions that your change
> is based on.
Before my change the second PT would also not be included in
obj->textsize since we were setting obj->textsize as end of
PT_LOAD[0].
After the change it will be end of last executable PT_LOAD (which will
usually be PT_LOAD[0] but could also include more now).
Since there is only one executable PT_LOAD which happens to be also be
PT_LOAD[0], there will be no change to obj->textsize.
The only time this commit could change anything is if there is a
PT_LOAD that is executable but is not PT_LOAD[0] or if PT_LOAD[0] is
not executable.
I think it must be the former case since as far as I know ld.bfd will
always create a read/execute segment as PT_LOAD[0] unless it is given
a custom linker script.
Alex
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