This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
RISC-V maintainer review of glibc patch needed (was: Re: [PATCH] riscv: Remove support for variable page sizes)
- From: Florian Weimer <fweimer at redhat dot com>
- To: libc-alpha at sourceware dot org, isa-dev at groups dot riscv dot org, linux-riscv at lists dot infradead dot org
- Cc: Palmer Dabbelt <palmer at sifive dot com>, Jim Wilson <jimw at sifive dot com>, DJ Delorie <dj at redhat dot com>, andrew at sifive dot com, krste at berkeley dot edu, binutils at sourceware dot org, gcc at gcc dot gnu dot org
- Date: Mon, 07 Oct 2019 18:21:12 +0200
- Subject: RISC-V maintainer review of glibc patch needed (was: Re: [PATCH] riscv: Remove support for variable page sizes)
- References: <87r23y2br3.fsf@oldenburg2.str.redhat.com>
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 */