Re: [PULL REQUEST v2] FDPIC ELF support for ARM

[Al Viro <viro@zeniv.linux.org.uk>]

On Mon, Jun 08, 2020 at 11:48:27PM -0400, Nicolas Pitre wrote:

> I suspect riscv will end up in the same situation when they upstream 
> their fdpic support.

FWIW, one thing that needs to be done is switching fdpic to use
of regset, a-la normal elf coredumps on the same arm.  I really want
to kill the sodding elf_core_copy_task_fpregs(), dump_fpu(),
etc.

Right now that crap is used by
	elf coredump on alpha c6x csky h8300 m68k microblaze nds32 um unicore32
	fdpic coredump on arm sh/nommu and c6x

Out of those only alpha, m68k, microblaze, um and unicore32 lack
regset - everything else (including all users of fdpic) have working ones.
And it's not at all hard to add the damn thing to those 5 architectures,
killing quite bit of code in binfmt_elf.c, as well as in arch/*

Note, BTW, that fdpic coredumps on arm currently have fucked FPU
for all but the main thread - arm has
int dump_fpu (struct pt_regs *regs, struct user_fp *fp)
{
        struct thread_info *thread = current_thread_info();
        int used_math = thread->used_cp[1] | thread->used_cp[2];

        if (used_math)
                memcpy(fp, &thread->fpstate.soft, sizeof (*fp));

        return used_math != 0;
}  
which obviously duplicates the contents of FP registers of the coredumping
thread into the NT_PRFPREG section for each thread...

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