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riscv: Remove support for variable page sizes

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_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.
This commit is contained in:
Florian Weimer 2019-10-07 19:03:50 +02:00
parent 0caab6638e
commit 921abe4729
4 changed files with 8 additions and 120 deletions
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8
ChangeLog
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@ -1,3 +1,11 @@
2019-10-07 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.
2019-10-07 Florian Weimer <fweimer@redhat.com>
nptl: Move pthread_attr_getschedparam implementation into libc.

4
sysdeps/unix/sysv/linux/riscv/Makefile
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@ -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)

84
sysdeps/unix/sysv/linux/riscv/dl-static.c
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@ -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

32
sysdeps/unix/sysv/linux/riscv/ldsodefs.h
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@ -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 */