From: "H.J. Lu" <hjl.tools@gmail.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Fāng-ruì Sòng" <maskray@google.com>,
libc-alpha@sourceware.org, binutils@sourceware.org
Subject: Re: [PATCH] elf: Support DT_RELR relative relocation format [BZ #27924]
Date: Tue, 12 Oct 2021 07:09:55 -0700 [thread overview]
Message-ID: <CAMe9rOrQX2mks78iwn94e8jFu8mTjRvs+DUUcUWX=h0p6aCLXg@mail.gmail.com> (raw)
In-Reply-To: <b5514c3f-7ac6-3a39-619f-0c580fb75a7e@suse.com>
On Tue, Oct 12, 2021 at 1:18 AM Jan Beulich via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On 11.10.2021 20:43, Fāng-ruì Sòng wrote:
> > On Mon, Oct 11, 2021 at 12:48 AM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 08.10.2021 08:57, Fangrui Song via Binutils wrote:
> >>> --- a/elf/dynamic-link.h
> >>> +++ b/elf/dynamic-link.h
> >>> @@ -192,6 +192,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
> >>> # define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
> >>> # endif
> >>>
> >>> +# define ELF_DYNAMIC_DO_RELR(map) \
> >>> + do { \
> >>> + ElfW(Addr) l_addr = (map)->l_addr, base = 0, start; \
> >>> + const ElfW(Relr) *r = 0, *end = 0; \
> >>> + if (!(map)->l_info[DT_RELR]) \
> >>> + break; \
> >>> + start = D_PTR((map), l_info[DT_RELR]); \
> >>> + r = (const ElfW(Relr) *)start; \
> >>> + end = (const ElfW(Relr) *)(start + (map)->l_info[DT_RELRSZ]->d_un.d_val); \
> >>> + for (; r < end; ++r) { \
> >>> + ElfW(Relr) entry = *r; \
> >>> + if ((entry & 1) == 0) { \
> >>> + *((ElfW(Addr) *)(l_addr + entry)) += l_addr; \
> >>> + base = entry + sizeof(ElfW(Addr)); \
> >>> + continue; \
> >>> + } \
> >>> + ElfW(Addr) offset = base; \
> >>> + do { \
> >>> + entry >>= 1; \
> >>> + if ((entry & 1) != 0) \
> >>> + *((ElfW(Addr) *)(l_addr + offset)) += l_addr; \
> >>> + offset += sizeof(ElfW(Addr)); \
> >>> + } while (entry != 0); \
> >>> + base += (8 * sizeof(ElfW(Relr)) - 1) * sizeof(ElfW(Addr)); \
> >>
> >> While in line with the proposed spec additions I'm afraid the uses of
> >> ElfW(Addr) here aren't universally correct: You assume that ELF
> >> container type (size) expresses an aspect of the ABI. While this is
> >> indeed the case for several arch-es, I think this has been a mistake.
> >> IA-64, while meanwhile mostly dead, is (was) an example where 64-bit
> >> code can validly live in a 32-bit ELF container (at least as far as
> >> the psABI is concerned; I have no idea whether glibc actually
> >> followed the spec). There's a separate ELF header flag indicating the
> >> ABI, and hence the size of a pointer.
> >
> > Thanks for chiming in.
> >
> > As of ia64 buildability, it works for me:
> >
> > scripts/build-many-glibcs.py /tmp/glibc-many compilers ia64-linux-gnu
> > mkdir -p out/ia64; cd out/ia64
> > ../../configure --prefix=/tmp/glibc/ia64 --host=ia64-linux-gnu
> > CC=/tmp/glibc-many/install/compilers/ia64-linux-gnu/bin/ia64-glibc-linux-gnu-gcc
> > CXX=/tmp/glibc-many/install/compilers/ia64-linux-gnu/bin/ia64-glibc-linux-gnu-g++
> > make -j 50
>
> I didn't suggest the build would fail. What I said is that I don't
> think the code is correct there.
>
> > As of the actual functionality, ugh, I cannot find ia64 in my Debian
> > testing's qemu-user-static package:( So I cannot test.
> >
> > That said, gold and LLD don't support ia64.
> > If we have a concern that ia64 may not work, the GNU ld maintainers
> > can simply not add ia64 support:)
>
> But you realize that I took ia64 only as example, as that's where
> I know ABI (pointer size) and ELF container size aren't connected.
> As per my looking at merely EF_MIPS_* in context of reading
> Joseph's reply, it might be that MIPS is another such example. But
> I lack sufficient knowledge of MIPS ...
>
The new code should be tested and verified on all supported
targets. That is another reason to implement this in binutils
ld first.
--
H.J.
next prev parent reply other threads:[~2021-10-12 14:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 6:57 Fangrui Song
2021-10-08 15:39 ` Florian Weimer
2021-10-08 16:36 ` Fangrui Song
2021-10-08 19:41 ` Cary Coutant
2021-10-08 16:51 ` H.J. Lu
2021-10-08 17:37 ` Fangrui Song
2021-10-08 17:43 ` H.J. Lu
2021-10-08 18:46 ` Fangrui Song
2021-10-11 7:48 ` Jan Beulich
2021-10-11 18:43 ` Fāng-ruì Sòng
2021-10-11 22:08 ` Joseph Myers
2021-10-12 8:14 ` Jan Beulich
2021-10-12 8:18 ` Jan Beulich
2021-10-12 14:09 ` H.J. Lu [this message]
2021-10-12 16:07 ` Fāng-ruì Sòng
2021-10-13 6:00 ` Jan Beulich
2021-10-13 6:13 ` Fāng-ruì Sòng
2021-10-13 6:18 ` Fāng-ruì Sòng
2021-10-18 7:59 ` Jan Beulich
2021-10-16 20:22 ` Fangrui Song
2021-10-26 23:28 ` Cary Coutant
2021-10-11 21:47 ` Joseph Myers
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