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glibc/elf/dl-sysdep.c
Chung-Lin Tang 15a0c5730d elf: Fix slow DSO sorting behavior in dynamic loader (BZ #17645) 
This second patch contains the actual implementation of a new sorting algorithm
for shared objects in the dynamic loader, which solves the slow behavior that
the current "old" algorithm falls into when the DSO set contains circular
dependencies.

The new algorithm implemented here is simply depth-first search (DFS) to obtain
the Reverse-Post Order (RPO) sequence, a topological sort. A new l_visited:1
bitfield is added to struct link_map to more elegantly facilitate such a search.

The DFS algorithm is applied to the input maps[nmap-1] backwards towards
maps[0]. This has the effect of a more "shallow" recursion depth in general
since the input is in BFS. Also, when combined with the natural order of
processing l_initfini[] at each node, this creates a resulting output sorting
closer to the intuitive "left-to-right" order in most cases.

Another notable implementation adjustment related to this _dl_sort_maps change
is the removing of two char arrays 'used' and 'done' in _dl_close_worker to
represent two per-map attributes. This has been changed to simply use two new
bit-fields l_map_used:1, l_map_done:1 added to struct link_map. This also allows
discarding the clunky 'used' array sorting that _dl_sort_maps had to sometimes
do along the way.

Tunable support for switching between different sorting algorithms at runtime is
also added. A new tunable 'glibc.rtld.dynamic_sort' with current valid values 1
(old algorithm) and 2 (new DFS algorithm) has been added. At time of commit
of this patch, the default setting is 1 (old algorithm).

Signed-off-by: Chung-Lin Tang  <cltang@codesourcery.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
2021-10-21 11:23:53 -03:00

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/* Operating system support for run-time dynamic linker. Generic Unix version.
Copyright (C) 1995-2021 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/>. */
/* We conditionalize the whole of this file rather than simply eliding it
from the static build, because other sysdeps/ versions of this file
might define things needed by a static build. */
#ifdef SHARED
#include <assert.h>
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <libintl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <ldsodefs.h>
#include <_itoa.h>
#include <fpu_control.h>
#include <entry.h>
#include <dl-machine.h>
#include <dl-procinfo.h>
#include <dl-osinfo.h>
#include <libc-internal.h>
#include <tls.h>
#include <dl-tunables.h>
#include <dl-auxv.h>
#include <dl-hwcap-check.h>
extern char **_environ attribute_hidden;
extern char _end[] attribute_hidden;
/* Protect SUID program against misuse of file descriptors. */
extern void __libc_check_standard_fds (void);
#ifdef NEED_DL_BASE_ADDR
ElfW(Addr) _dl_base_addr;
#endif
int __libc_enable_secure attribute_relro = 0;
rtld_hidden_data_def (__libc_enable_secure)
/* This variable contains the lowest stack address ever used. */
void *__libc_stack_end attribute_relro = NULL;
rtld_hidden_data_def(__libc_stack_end)
void *_dl_random attribute_relro = NULL;
#ifndef DL_FIND_ARG_COMPONENTS
# define DL_FIND_ARG_COMPONENTS(cookie, argc, argv, envp, auxp) \
do { \
void **_tmp; \
(argc) = *(long int *) cookie; \
(argv) = (char **) ((long int *) cookie + 1); \
(envp) = (argv) + (argc) + 1; \
for (_tmp = (void **) (envp); *_tmp; ++_tmp) \
continue; \
(auxp) = (void *) ++_tmp; \
} while (0)
#endif
#ifndef DL_STACK_END
# define DL_STACK_END(cookie) ((void *) (cookie))
#endif
ElfW(Addr)
_dl_sysdep_start (void **start_argptr,
void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
{
const ElfW(Phdr) *phdr = NULL;
ElfW(Word) phnum = 0;
ElfW(Addr) user_entry;
ElfW(auxv_t) *av;
#ifdef HAVE_AUX_SECURE
# define set_seen(tag) (tag) /* Evaluate for the side effects. */
# define set_seen_secure() ((void) 0)
#else
uid_t uid = 0;
gid_t gid = 0;
unsigned int seen = 0;
# define set_seen_secure() (seen = -1)
# ifdef HAVE_AUX_XID
# define set_seen(tag) (tag) /* Evaluate for the side effects. */
# else
# define M(type) (1 << (type))
# define set_seen(tag) seen |= M ((tag)->a_type)
# endif
#endif
#ifdef NEED_DL_SYSINFO
uintptr_t new_sysinfo = 0;
#endif
__libc_stack_end = DL_STACK_END (start_argptr);
DL_FIND_ARG_COMPONENTS (start_argptr, _dl_argc, _dl_argv, _environ,
GLRO(dl_auxv));
user_entry = (ElfW(Addr)) ENTRY_POINT;
GLRO(dl_platform) = NULL; /* Default to nothing known about the platform. */
/* NB: Default to a constant CONSTANT_MINSIGSTKSZ. */
_Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
"CONSTANT_MINSIGSTKSZ is constant");
GLRO(dl_minsigstacksize) = CONSTANT_MINSIGSTKSZ;
for (av = GLRO(dl_auxv); av->a_type != AT_NULL; set_seen (av++))
switch (av->a_type)
{
case AT_PHDR:
phdr = (void *) av->a_un.a_val;
break;
case AT_PHNUM:
phnum = av->a_un.a_val;
break;
case AT_PAGESZ:
GLRO(dl_pagesize) = av->a_un.a_val;
break;
case AT_ENTRY:
user_entry = av->a_un.a_val;
break;
#ifdef NEED_DL_BASE_ADDR
case AT_BASE:
_dl_base_addr = av->a_un.a_val;
break;
#endif
#ifndef HAVE_AUX_SECURE
case AT_UID:
case AT_EUID:
uid ^= av->a_un.a_val;
break;
case AT_GID:
case AT_EGID:
gid ^= av->a_un.a_val;
break;
#endif
case AT_SECURE:
#ifndef HAVE_AUX_SECURE
seen = -1;
#endif
__libc_enable_secure = av->a_un.a_val;
break;
case AT_PLATFORM:
GLRO(dl_platform) = (void *) av->a_un.a_val;
break;
case AT_HWCAP:
GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
break;
case AT_HWCAP2:
GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
break;
case AT_CLKTCK:
GLRO(dl_clktck) = av->a_un.a_val;
break;
case AT_FPUCW:
GLRO(dl_fpu_control) = av->a_un.a_val;
break;
#ifdef NEED_DL_SYSINFO
case AT_SYSINFO:
new_sysinfo = av->a_un.a_val;
break;
#endif
#ifdef NEED_DL_SYSINFO_DSO
case AT_SYSINFO_EHDR:
GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
break;
#endif
case AT_RANDOM:
_dl_random = (void *) av->a_un.a_val;
break;
case AT_MINSIGSTKSZ:
GLRO(dl_minsigstacksize) = av->a_un.a_val;
break;
DL_PLATFORM_AUXV
}
dl_hwcap_check ();
#ifndef HAVE_AUX_SECURE
if (seen != -1)
{
/* Fill in the values we have not gotten from the kernel through the
auxiliary vector. */
# ifndef HAVE_AUX_XID
# define SEE(UID, var, uid) \
if ((seen & M (AT_##UID)) == 0) var ^= __get##uid ()
SEE (UID, uid, uid);
SEE (EUID, uid, euid);
SEE (GID, gid, gid);
SEE (EGID, gid, egid);
# endif
/* If one of the two pairs of IDs does not match this is a setuid
or setgid run. */
__libc_enable_secure = uid | gid;
}
#endif
#ifndef HAVE_AUX_PAGESIZE
if (GLRO(dl_pagesize) == 0)
GLRO(dl_pagesize) = __getpagesize ();
#endif
#ifdef NEED_DL_SYSINFO
if (new_sysinfo != 0)
{
# ifdef NEED_DL_SYSINFO_DSO
/* Only set the sysinfo value if we also have the vsyscall DSO. */
if (GLRO(dl_sysinfo_dso) != 0)
# endif
GLRO(dl_sysinfo) = new_sysinfo;
}
#endif
__tunables_init (_environ);
/* Initialize DSO sorting algorithm after tunables. */
_dl_sort_maps_init ();
#ifdef DL_SYSDEP_INIT
DL_SYSDEP_INIT;
#endif
#ifdef DL_PLATFORM_INIT
DL_PLATFORM_INIT;
#endif
/* Determine the length of the platform name. */
if (GLRO(dl_platform) != NULL)
GLRO(dl_platformlen) = strlen (GLRO(dl_platform));
if (__sbrk (0) == _end)
/* The dynamic linker was run as a program, and so the initial break
starts just after our bss, at &_end. The malloc in dl-minimal.c
will consume the rest of this page, so tell the kernel to move the
break up that far. When the user program examines its break, it
will see this new value and not clobber our data. */
__sbrk (GLRO(dl_pagesize)
- ((_end - (char *) 0) & (GLRO(dl_pagesize) - 1)));
/* If this is a SUID program we make sure that FDs 0, 1, and 2 are
allocated. If necessary we are doing it ourself. If it is not
possible we stop the program. */
if (__builtin_expect (__libc_enable_secure, 0))
__libc_check_standard_fds ();
(*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
return user_entry;
}
void
_dl_sysdep_start_cleanup (void)
{
}
void
_dl_show_auxv (void)
{
char buf[64];
ElfW(auxv_t) *av;
/* Terminate string. */
buf[63] = '\0';
/* The following code assumes that the AT_* values are encoded
starting from 0 with AT_NULL, 1 for AT_IGNORE, and all other values
close by (otherwise the array will be too large). In case we have
to support a platform where these requirements are not fulfilled
some alternative implementation has to be used. */
for (av = GLRO(dl_auxv); av->a_type != AT_NULL; ++av)
{
static const struct
{
const char label[22];
enum { unknown = 0, dec, hex, str, ignore } form : 8;
} auxvars[] =
{
[AT_EXECFD - 2] = { "EXECFD: ", dec },
[AT_EXECFN - 2] = { "EXECFN: ", str },
[AT_PHDR - 2] = { "PHDR: 0x", hex },
[AT_PHENT - 2] = { "PHENT: ", dec },
[AT_PHNUM - 2] = { "PHNUM: ", dec },
[AT_PAGESZ - 2] = { "PAGESZ: ", dec },
[AT_BASE - 2] = { "BASE: 0x", hex },
[AT_FLAGS - 2] = { "FLAGS: 0x", hex },
[AT_ENTRY - 2] = { "ENTRY: 0x", hex },
[AT_NOTELF - 2] = { "NOTELF: ", hex },
[AT_UID - 2] = { "UID: ", dec },
[AT_EUID - 2] = { "EUID: ", dec },
[AT_GID - 2] = { "GID: ", dec },
[AT_EGID - 2] = { "EGID: ", dec },
[AT_PLATFORM - 2] = { "PLATFORM: ", str },
[AT_HWCAP - 2] = { "HWCAP: ", hex },
[AT_CLKTCK - 2] = { "CLKTCK: ", dec },
[AT_FPUCW - 2] = { "FPUCW: ", hex },
[AT_DCACHEBSIZE - 2] = { "DCACHEBSIZE: 0x", hex },
[AT_ICACHEBSIZE - 2] = { "ICACHEBSIZE: 0x", hex },
[AT_UCACHEBSIZE - 2] = { "UCACHEBSIZE: 0x", hex },
[AT_IGNOREPPC - 2] = { "IGNOREPPC", ignore },
[AT_SECURE - 2] = { "SECURE: ", dec },
[AT_BASE_PLATFORM - 2] = { "BASE_PLATFORM: ", str },
[AT_SYSINFO - 2] = { "SYSINFO: 0x", hex },
[AT_SYSINFO_EHDR - 2] = { "SYSINFO_EHDR: 0x", hex },
[AT_RANDOM - 2] = { "RANDOM: 0x", hex },
[AT_HWCAP2 - 2] = { "HWCAP2: 0x", hex },
[AT_MINSIGSTKSZ - 2] = { "MINSIGSTKSZ: ", dec },
[AT_L1I_CACHESIZE - 2] = { "L1I_CACHESIZE: ", dec },
[AT_L1I_CACHEGEOMETRY - 2] = { "L1I_CACHEGEOMETRY: 0x", hex },
[AT_L1D_CACHESIZE - 2] = { "L1D_CACHESIZE: ", dec },
[AT_L1D_CACHEGEOMETRY - 2] = { "L1D_CACHEGEOMETRY: 0x", hex },
[AT_L2_CACHESIZE - 2] = { "L2_CACHESIZE: ", dec },
[AT_L2_CACHEGEOMETRY - 2] = { "L2_CACHEGEOMETRY: 0x", hex },
[AT_L3_CACHESIZE - 2] = { "L3_CACHESIZE: ", dec },
[AT_L3_CACHEGEOMETRY - 2] = { "L3_CACHEGEOMETRY: 0x", hex },
};
unsigned int idx = (unsigned int) (av->a_type - 2);
if ((unsigned int) av->a_type < 2u
|| (idx < sizeof (auxvars) / sizeof (auxvars[0])
&& auxvars[idx].form == ignore))
continue;
assert (AT_NULL == 0);
assert (AT_IGNORE == 1);
/* Some entries are handled in a special way per platform. */
if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
continue;
if (idx < sizeof (auxvars) / sizeof (auxvars[0])
&& auxvars[idx].form != unknown)
{
const char *val = (char *) av->a_un.a_val;
if (__builtin_expect (auxvars[idx].form, dec) == dec)
val = _itoa ((unsigned long int) av->a_un.a_val,
buf + sizeof buf - 1, 10, 0);
else if (__builtin_expect (auxvars[idx].form, hex) == hex)
val = _itoa ((unsigned long int) av->a_un.a_val,
buf + sizeof buf - 1, 16, 0);
_dl_printf ("AT_%s%s\n", auxvars[idx].label, val);
continue;
}
/* Unknown value: print a generic line. */
char buf2[17];
buf2[sizeof (buf2) - 1] = '\0';
const char *val2 = _itoa ((unsigned long int) av->a_un.a_val,
buf2 + sizeof buf2 - 1, 16, 0);
const char *val = _itoa ((unsigned long int) av->a_type,
buf + sizeof buf - 1, 16, 0);
_dl_printf ("AT_??? (0x%s): 0x%s\n", val, val2);
}
}
#endif
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