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

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

[Florian Weimer]

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 */

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