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hurd: Rework sbrk

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Making the brk start exactly at the end of the main application binary was
requiring to get it through the _end symbol, which does not work any more
with recent toolchains, and actually produces in libc.so a confusing
external _end symbol that produces odd results, see
https://sourceware.org/bugzilla/show_bug.cgi?id=23499

Trying to do so is quite outdated anyway with the tendency for address
randomization.

Using _end was also allowing to include the main binary data within
the RLIMIT_DATA, but this also seems outdated with dynamic library
loading, and nowadays' memory consumption via malloc and mmap rather than
statically-allocated data.

This adds a BRK_START macro in <vm_param.h> that just tells where we
want to start the brk, and thus removes the _end symbol.

* sysdeps/mach/hurd/i386/vm_param.h: New file.
* sysdeps/mach/hurd/brk.c: Use BRK_START as brk start instead of _end.
Also ignore __data_start.
* hurd/Versions: Remove _end symbol.
* sysdeps/mach/hurd/i386/libc.abilist: Remove _end symbol.
This commit is contained in:
Samuel Thibault 2020-08-05 23:48:58 +02:00
parent ce62504488
commit 8c6beab4e1
4 changed files with 32 additions and 12 deletions
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3
hurd/Versions
View file

@ -1,8 +1,5 @@
libc {
GLIBC_2.0 {
# necessary for the Hurd brk implementation
_end;
# variables used in macros & inline functions
__hurd_threadvar_stack_mask; __hurd_threadvar_stack_offset;

16
sysdeps/mach/hurd/brk.c
View file

@ -19,6 +19,7 @@
#include <hurd.h>
#include <hurd/resource.h>
#include <cthreads.h> /* For `struct mutex'. */
#include <vm_param.h>
/* Initial maximum size of the data segment (this is arbitrary). */
@ -39,9 +40,7 @@ weak_alias (_hurd_brk, ___brk_addr)
struct mutex _hurd_brk_lock;
extern int __data_start, _end;
weak_extern (__data_start)
static vm_address_t static_data_start;
static vm_address_t brk_start;
/* Set the end of the process's data space to INADDR.
@ -91,7 +90,7 @@ _hurd_set_brk (vm_address_t addr)
rlimit = _hurd_rlimits[RLIMIT_DATA].rlim_cur;
__mutex_unlock (&_hurd_rlimit_lock);
if (addr - static_data_start > rlimit)
if (addr - brk_start > rlimit)
{
/* Need to increase the resource limit. */
errno = ENOMEM;
@ -138,17 +137,18 @@ init_brk (void)
__mutex_init (&_hurd_brk_lock);
static_data_start = (vm_address_t) (&__data_start ?: &_end);
brk_start = (vm_address_t) BRK_START;
/* If _hurd_brk is already set, don't change it. The assumption is that
it was set in a previous run before something like Emacs's unexec was
called and dumped all the data up to the break at that point. */
if (_hurd_brk == 0)
_hurd_brk = (vm_address_t) &_end;
if (_hurd_brk == 0) {
_hurd_brk = (vm_address_t) BRK_START;
}
pagend = round_page (_hurd_brk);
_hurd_data_end = round_page (static_data_start + DATA_SIZE);
_hurd_data_end = round_page (brk_start + DATA_SIZE);
if (pagend < _hurd_data_end)
{

1
sysdeps/mach/hurd/i386/libc.abilist
View file

@ -554,7 +554,6 @@ GLIBC_2.2.6 __xstat64 F
GLIBC_2.2.6 _authenticate F
GLIBC_2.2.6 _dl_mcount_wrapper F
GLIBC_2.2.6 _dl_mcount_wrapper_check F
GLIBC_2.2.6 _end D 0x0
GLIBC_2.2.6 _environ D 0x4
GLIBC_2.2.6 _exit F
GLIBC_2.2.6 _flushlbf F

24
sysdeps/mach/hurd/i386/vm_param.h Normal file
View file

@ -0,0 +1,24 @@
/* Copyright (C) 2020 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 _I386_VM_PARAM_H
#define _I386_VM_PARAM_H
/* Arbitrary start of the brk. This is after usual binary and library mappings. */
#define BRK_START 0x10000000
#endif /* i386/vm_param.h */