Re: RISC-V maintainer review of glibc patch needed (was: Re: [PATCH] riscv: Remove support for variable page sizes)

[Andrew Waterman <andrew@sifive.com>]

LGTM; I believe you are right on both counts that this was borrowed
from MIPS and that we do not need this for RISC-V.

On Mon, Oct 7, 2019 at 6:21 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> Ping.  I need a review of this glibc patch from a RISC-V architecture
> maintainer:
>
>   <https://sourceware.org/ml/libc-alpha/2019-09/msg00506.html>
>
> I believe this is another artifact needlessly copied over from the MIPS
> port of glibc, but this one we can fix easily.
>
> Thanks,
> Florian
>
> * Florian Weimer:
>
> > _dl_var_init is used to patch the read-only data section after
> > relocation.  Several architectures use this to update
> > GLRO(page_size) with the correct value for the static dlopen case,
> > where _rtld_global_ro has not been initialized by the dynamic
> > loader.
> >
> > RISC-V does not need this.  The RISC-V Instruction Set Manual,
> > Volume II: Privileged Architecture, Document Version
> > 20190608-Priv-MSU-Ratified says this:
> >
> >     After much deliberation, we have settled on a conventional
> >     page size of 4 KiB for both RV32 and RV64. We expect this
> >     decision to ease the porting of low-level runtime software
> >     and device drivers. The TLB reach problem is ameliorated by
> >     transparent superpage support in modern operating systems
> >     [2]. Additionally, multi-level TLB hierarchies are quite
> >     inexpensive relative to the multi-level cache hierarchies
> >     whose address space they map.
> >
> >     [2] Juan Navarro, Sitaram Iyer, Peter Druschel, and
> >       Alan Cox. Practical, transparent operating system support
> >       for superpages.  SIGOPS Oper. Syst. Rev., 36(SI):89–104,
> >       December 2002.
> >
> > This means that the initialization of
> > _rtld_global_ro._dl_page_size in elf/rtld.c with EXEC_PAGESIZE
> > is sufficient for RISC-V.
> >
> > 2019-09-30  Florian Weimer  <fweimer@redhat.com>
> >
> >       riscv: Remove support for variable page sizes.
> >       * sysdeps/unix/sysv/linux/riscv/Makefile [$(subdir) == elf]
> >       (sysdep_routines): Do not add dl-static.
> >       * sysdeps/unix/sysv/linux/riscv/dl-static.c: Remove file.
> >       * sysdeps/unix/sysv/linux/riscv/ldsodefs.h: Likewise.
> >
> > diff --git a/sysdeps/unix/sysv/linux/riscv/Makefile b/sysdeps/unix/sysv/linux/riscv/Makefile
> > index b47858769f..b7ad31885c 100644
> > --- a/sysdeps/unix/sysv/linux/riscv/Makefile
> > +++ b/sysdeps/unix/sysv/linux/riscv/Makefile
> > @@ -1,9 +1,5 @@
> >  ifeq ($(subdir),elf)
> >  sysdep_routines      += dl-vdso
> > -ifeq ($(build-shared),yes)
> > -# This is needed for DSO loading from static binaries.
> > -sysdep-dl-routines += dl-static
> > -endif
> >  endif
> >
> >  ifeq ($(subdir),misc)
> > diff --git a/sysdeps/unix/sysv/linux/riscv/dl-static.c b/sysdeps/unix/sysv/linux/riscv/dl-static.c
> > deleted file mode 100644
> > index e52612a267..0000000000
> > --- a/sysdeps/unix/sysv/linux/riscv/dl-static.c
> > +++ /dev/null
> > @@ -1,84 +0,0 @@
> > -/* Variable initialization.  RISC-V version
> > -   Copyright (C) 2001-2019 Free Software Foundation, Inc.
> > -   This file is part of the GNU C Library.
> > -
> > -   The GNU C Library is free software; you can redistribute it and/or
> > -   modify it under the terms of the GNU Lesser General Public
> > -   License as published by the Free Software Foundation; either
> > -   version 2.1 of the License, or (at your option) any later version.
> > -
> > -   The GNU C Library is distributed in the hope that it will be useful,
> > -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > -   Lesser General Public License for more details.
> > -
> > -   You should have received a copy of the GNU Lesser General Public
> > -   License along with the GNU C Library.  If not, see
> > -   <https://www.gnu.org/licenses/>.  */
> > -
> > -#include <ldsodefs.h>
> > -
> > -#ifdef SHARED
> > -
> > -void
> > -_dl_var_init (void *array[])
> > -{
> > -  /* It has to match "variables" below.  */
> > -  enum
> > -    {
> > -      DL_PAGESIZE = 0
> > -    };
> > -
> > -  GLRO(dl_pagesize) = *((size_t *) array[DL_PAGESIZE]);
> > -}
> > -
> > -#else
> > -
> > -static void *variables[] =
> > -{
> > -  &GLRO(dl_pagesize)
> > -};
> > -
> > -static void
> > -_dl_unprotect_relro (struct link_map *l)
> > -{
> > -  ElfW(Addr) start = ((l->l_addr + l->l_relro_addr)
> > -                   & ~(GLRO(dl_pagesize) - 1));
> > -  ElfW(Addr) end = ((l->l_addr + l->l_relro_addr + l->l_relro_size)
> > -                 & ~(GLRO(dl_pagesize) - 1));
> > -
> > -  if (start != end)
> > -    __mprotect ((void *) start, end - start, PROT_READ | PROT_WRITE);
> > -}
> > -
> > -void
> > -_dl_static_init (struct link_map *l)
> > -{
> > -  struct link_map *rtld_map = l;
> > -  struct r_scope_elem **scope;
> > -  const ElfW(Sym) *ref = NULL;
> > -  lookup_t loadbase;
> > -  void (*f) (void *[]);
> > -  size_t i;
> > -
> > -  loadbase = _dl_lookup_symbol_x ("_dl_var_init", l, &ref, l->l_local_scope,
> > -                               NULL, 0, 1, NULL);
> > -
> > -  for (scope = l->l_local_scope; *scope != NULL; scope++)
> > -    for (i = 0; i < (*scope)->r_nlist; i++)
> > -      if ((*scope)->r_list[i] == loadbase)
> > -     {
> > -       rtld_map = (*scope)->r_list[i];
> > -       break;
> > -     }
> > -
> > -  if (ref != NULL)
> > -    {
> > -      f = (void (*) (void *[])) DL_SYMBOL_ADDRESS (loadbase, ref);
> > -      _dl_unprotect_relro (rtld_map);
> > -      f (variables);
> > -      _dl_protect_relro (rtld_map);
> > -    }
> > -}
> > -
> > -#endif
> > diff --git a/sysdeps/unix/sysv/linux/riscv/ldsodefs.h b/sysdeps/unix/sysv/linux/riscv/ldsodefs.h
> > deleted file mode 100644
> > index a46e676752..0000000000
> > --- a/sysdeps/unix/sysv/linux/riscv/ldsodefs.h
> > +++ /dev/null
> > @@ -1,32 +0,0 @@
> > -/* RISC-V dynamic linker data structures for loaded ELF shared objects.
> > -   Copyright (C) 2001-2019 Free Software Foundation, Inc.
> > -   This file is part of the GNU C Library.
> > -
> > -   The GNU C Library is free software; you can redistribute it and/or
> > -   modify it under the terms of the GNU Lesser General Public
> > -   License as published by the Free Software Foundation; either
> > -   version 2.1 of the License, or (at your option) any later version.
> > -
> > -   The GNU C Library is distributed in the hope that it will be useful,
> > -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > -   Lesser General Public License for more details.
> > -
> > -   You should have received a copy of the GNU Lesser General Public
> > -   License along with the GNU C Library.  If not, see
> > -   <https://www.gnu.org/licenses/>.  */
> > -
> > -#ifndef      _LDSODEFS_H
> > -
> > -/* Get the real definitions.  */
> > -#include_next <ldsodefs.h>
> > -
> > -/* Now define our stuff.  */
> > -
> > -/* We need special support to initialize DSO loaded for statically linked
> > -   binaries.  */
> > -extern void _dl_static_init (struct link_map *map);
> > -#undef DL_STATIC_INIT
> > -#define DL_STATIC_INIT(map) _dl_static_init (map)
> > -
> > -#endif /* ldsodefs.h */