On Tue, 30 Oct 2018 at 22:16, Mark Millard <marklmi26-f...@yahoo.com> wrote: > > On 2018-Oct-30, at 2:40 PM, Alexander Richardson <arichardson at freebsd.org> > wrote: > > > 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. > > I do not see any evidence that PF_X would match the tests for either > of the following from the 2nd PT_LOAD: > > 19 .got 00000098 0000000010019800 0000000010019800 00009800 2**8 > CONTENTS, ALLOC, LOAD, DATA > 20 .plt 00000708 0000000010019898 0000000010019898 00009898 2**3 > ALLOC > > in the likes of: > > 135 if ((segs[nsegs]->p_flags & PF_X) == PF_X) { > 136 text_end = MAX(text_end, > 137 round_page(segs[nsegs]->p_vaddr + > segs[nsegs]->p_memsz)); > 138 } > > in map_object.c > > This is possibly to avoid: > > 467 if (elfflags & PF_X) > 468 prot |= PROT_EXEC; > > because of writable code. > > > rtld.c also, for: > > 1397 nsegs++; > 1398 if ((ph->p_flags & PF_X) == PF_X) { > 1399 obj->textsize = MAX(obj->textsize, > 1400 round_page(ph->p_vaddr + ph->p_memsz) - > obj->vaddrbase); > 1401 } > > Still, I may be missing something in my understanding. >
Before this change obj->textsize was always set as the end of PT_LOAD[0]. Now it will contain everything up to the end of the last PT_LOAD with execute permissions. In the binary you dumped this is PT_LOAD[0] both before and after the patch so there is no change in behaviour. The .got and .plt we not included in textsize before this patch either. Therefore the only way I can see this patch breaking anything is if the PHDRS of one of the loaded libraries causes a change in behaviour. Alex _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"