/usr/bin/ld.lld on powerpc64: produces a.out for which: ld-elf.so.1: assert failed: /usr/src/libexec/rtld-elf/powerpc64/reloc.c:374

[Roman Divacky]

Go with Out.

On Tue, Jan 17, 2017 at 01:53:14PM -0800, Mark Millard wrote:
> On 2017-Jan-17, at 11:54 AM, Roman Divacky <rdivacky at vlakno.cz> wrote:
> 
> . . .
> > I wonder if it doesnt work because of my first patch (the one to turn GOT
> > reloc into PLT one).
> > 
> > LLD understands that we use GOT as TOC (which was true before my patch),
> > I wonder if something like this:
> > 
> > ndex: tools/lld/ELF/Target.cpp
> > ===================================================================
> > --- tools/lld/ELF/Target.cpp	(revision 292071)
> > +++ tools/lld/ELF/Target.cpp	(working copy)
> > @@ -1070,7 +1070,8 @@
> > }
> > 
> > PPC64TargetInfo::PPC64TargetInfo() {
> > -  PltRel = GotRel = R_PPC64_GLOB_DAT;
> > +  GotRel = R_PPC64_GLOB_DAT;
> > +  PltRel = R_PPC64_JMP_SLOT;
> >   RelativeRel = R_PPC64_RELATIVE;
> >   GotEntrySize = 8;
> >   GotPltEntrySize = 8;
> > @@ -1099,7 +1100,7 @@
> >   // TOC starts where the first of these sections starts. We always create a
> >   // .got when we see a relocation that uses it, so for us the start is always
> >   // the .got.
> > -  uint64_t TocVA = In<ELF64BE>::Got->getVA();
> > +  uint64_t TocVA = In<ELF64BE>::Plt->getVA();
> > 
> >   // Per the ppc64-elf-linux ABI, The TOC base is TOC value plus 0x8000
> >   // thus permitting a full 64 Kbytes segment. Note that the glibc startup
> 
> The modern 3.9.1 source does not match for the last. Note the
> "Out" vs. "In" below ("svnlite status" does not show my source
> as different in this area):
> 
> uint64_t getPPC64TocBase() {
>   // The TOC consists of sections .got, .toc, .tocbss, .plt in that order. The
>   // TOC starts where the first of these sections starts. We always create a
>   // .got when we see a relocation that uses it, so for us the start is always
>   // the .got.
>   uint64_t TocVA = Out<ELF64BE>::Got->getVA();
>       
>   // Per the ppc64-elf-linux ABI, The TOC base is TOC value plus 0x8000
>   // thus permitting a full 64 Kbytes segment. Note that the glibc startup
>   // code (crt1.o) assumes that you can get from the TOC base to the
>   // start of the .toc section with only a single (signed) 16-bit relocation.
>   return TocVA + PPC64TocOffset;
> }
> 
> [Also the "// TOC . . ." comment is at line 1005 (given the prior
> GotRel vs. PltRel split into separate lines).]
> 
> Which should I use?: In vs. Out
> 
> > would make any difference? It's not correct but might shed some light on what needs to be done
> > if I am right.
> 
> Separately if I understand the change you are picking out which section
> is first of .got, .toc, .tocbss, .plt (.got.plt as well?). But for the
> order of things that would still make the .ctors, .dtors, .jcr, .dynamic,
> and .data sections as being inside the TOC and taking TOC address range
> space:
> 
> 	0x0000000010010560 - 0x00000000100105c0 is .plt          <<<<<===== NOTE!!!!
> 	0x0000000010020000 - 0x0000000010020010 is .ctors
> 	0x0000000010020010 - 0x0000000010020020 is .dtors
> 	0x0000000010020020 - 0x0000000010020028 is .jcr
> 	0x0000000010020028 - 0x0000000010020138 is .dynamic
> 	0x0000000010020138 - 0x0000000010020138 is .got          <<<<<===== NOTE!!!!
> 	0x0000000010030000 - 0x0000000010030019 is .data
> 	0x0000000010030020 - 0x0000000010030050 is .got.plt      <<<<<===== NOTE!!!!
> 	0x0000000010030050 - 0x00000000100300a0 is .toc          <<<<<===== NOTE!!!!
> 
> Is that expected/desired/allowed?
> 
> > Could you explore this please?
> 
> After you report for sure for In vs. Out I'll take a stab
> at it.
> 
> ===
> Mark Millard
> markmi at dsl-only.net