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On 14 Sep 2015 12:09, Rich Felker wrote: > On Thu, Sep 10, 2015 at 04:53:35PM +0100, David Howells wrote: > > Rich Felker <dalias@libc.org> wrote: > > > On the other hand, the only existing way to produce a binary that both > > > (1) needs constant displacement, and (2) actually gets constant > > > displacement from the kernel at load time, is to manually edit the ELF > > > headers to flip the bit. So I really doubt any such binaries exist. Do > > > you have a reason to believe they do? > > > > Well, Fujitsu asked for it for FRV - I've no idea whether they have such > > binaries still. > > OK, I've solved part of the mystery: on FRV and Blackfin, binutils > matches the kernel behavior and conflicts with the (effectively wrong) > ABI documents. As can be seen at the following locations in the > source, EF_$ARCH_PIC is cleared by default and set when there is a > cross-segment relocation that forces constant displacement: > > Blackfin: > https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elf32-bfin.c;h=152134ee7b9b445d96818fcab2350ffd11795897;hb=HEAD#l3140 > https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elf32-bfin.c;h=152134ee7b9b445d96818fcab2350ffd11795897;hb=HEAD#l4978 it's a bit more complicated than that. only one place does Blackfin permit setting of EF_BFIN_PIC: https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elf32-bfin.c;h=152134ee7b9b445d96818fcab2350ffd11795897;hb=HEAD#l3140 and if you look before that, it has: if (!silence_segment_error && bfd_link_pic (info)) return FALSE; and those are defined as: int silence_segment_error = !bfd_link_pic (info); #define bfd_link_pic(info) (bfd_link_dll (info) || bfd_link_pie (info)) #define bfd_link_pie(info) ((info)->type == type_pie) all FDPIC ELFs must be PIE which means it's not possible to create a Blackfin FDPIC ELF with EF_BFIN_PIC set. off the top of my head, i don't recall seeing EF_BFIN_PIC being set in Blackfin FDPIC ELFs. it would show up when generating some FLAT code w/-fpic, but that doesn't matter here. > FRV: > https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elf32-frv.c;h=fa12528b3d11ab9ed7a4d5d894f8b9c1a5e783a9;hb=HEAD#l3919 > https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/elf32-frv.c;h=fa12528b3d11ab9ed7a4d5d894f8b9c1a5e783a9;hb=HEAD#l6367 the Blackfin code was copied from FRV, and the codepath i noted above is the same for FRV. -mike
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