[PATCH] D63869: [ELF] Do not produce DT_JMPREL and DT_PLTGOT if .rela.plt is empty.

Thu Jun 27 06:55:41 PDT 2019

MaskRay added inline comments.

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Comment at: test/ELF/empty-relaplt-dyntags.s:18
+## mentioned in the linker script. However, even in that case we should not
+## produce DT_JMPREL and DT_PLTGOT tags because this can cause a dynamic loader
+## to write into memory it considers reserved. In fact, as .got.plt is also
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ikudrin wrote:
> MaskRay wrote:
> > > to write into memory it considers reserved
> > 
> > I don't think a dynamic linker should do this because DT_PLTRELSZ is zero.
> > 
> > I agree that 0 JMPREL should be omitted.
> > 
> >  0x0000000000000017 (JMPREL)             0x0                                                             
> >  0x0000000000000002 (PLTRELSZ)           0 (bytes)
> >  0x0000000000000003 (PLTGOT)             0x0
> That is why I posted the reproducer. I tested it on Ubuntu 18.04 with the fresh built `lld`.
You are right :) glibc writes the slots unconditionally

.got.plt[1] = _dl_runtime_resolve, .got.plt[2] = link_map

I have no more comments if you can fix the echo indentation and move the test under linkerscript

Empty .rela.plt is kept due to the isDiscardable() logic in LinkerScript.cpp

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