dlfcn: Implement the RTLD_DI_PHDR request type for dlinfo

The information is theoretically available via dl_iterate_phdr as
well, but that approach is very slow if there are many shared
objects.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@rehdat.com>
This commit is contained in:
Florian Weimer 2022-04-29 17:00:53 +02:00
parent 93804a1ee0
commit d056c21213
5 changed files with 159 additions and 5 deletions

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@ -73,6 +73,10 @@ tststatic3-ENV = $(tststatic-ENV)
tststatic4-ENV = $(tststatic-ENV)
tststatic5-ENV = $(tststatic-ENV)
tests-internal += \
tst-dlinfo-phdr \
# tests-internal
ifneq (,$(CXX))
modules-names += bug-atexit3-lib
else

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@ -164,7 +164,12 @@ enum
segment, or if the calling thread has not allocated a block for it. */
RTLD_DI_TLS_DATA = 10,
RTLD_DI_MAX = 10
/* Treat ARG as const ElfW(Phdr) **, and store the address of the
program header array at that location. The dlinfo call returns
the number of program headers in the array. */
RTLD_DI_PHDR = 11,
RTLD_DI_MAX = 11
};

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@ -28,6 +28,10 @@ struct dlinfo_args
void *handle;
int request;
void *arg;
/* This is the value that is returned from dlinfo if no error is
signaled. */
int result;
};
static void
@ -40,6 +44,7 @@ dlinfo_doit (void *argsblock)
{
case RTLD_DI_CONFIGADDR:
default:
args->result = -1;
_dl_signal_error (0, NULL, NULL, N_("unsupported dlinfo request"));
break;
@ -75,6 +80,11 @@ dlinfo_doit (void *argsblock)
*(void **) args->arg = data;
break;
}
case RTLD_DI_PHDR:
*(const ElfW(Phdr) **) args->arg = l->l_phdr;
args->result = l->l_phnum;
break;
}
}
@ -82,7 +92,8 @@ static int
dlinfo_implementation (void *handle, int request, void *arg)
{
struct dlinfo_args args = { handle, request, arg };
return _dlerror_run (&dlinfo_doit, &args) ? -1 : 0;
_dlerror_run (&dlinfo_doit, &args);
return args.result;
}
#ifdef SHARED

125
dlfcn/tst-dlinfo-phdr.c Normal file
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@ -0,0 +1,125 @@
/* Test for dlinfo (RTLD_DI_PHDR).
Copyright (C) 2022 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 <dlfcn.h>
#include <link.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <sys/auxv.h>
#include <support/check.h>
#include <support/xdlfcn.h>
/* Used to verify that the program header array appears as expected
among the dl_iterate_phdr callback invocations. */
struct dlip_callback_args
{
struct link_map *l; /* l->l_addr is used to find the object. */
const ElfW(Phdr) *phdr; /* Expected program header pointed. */
int phnum; /* Expected program header count. */
bool found; /* True if l->l_addr has been found. */
};
static int
dlip_callback (struct dl_phdr_info *dlpi, size_t size, void *closure)
{
TEST_COMPARE (sizeof (*dlpi), size);
struct dlip_callback_args *args = closure;
if (dlpi->dlpi_addr == args->l->l_addr)
{
TEST_VERIFY (!args->found);
args->found = true;
TEST_VERIFY (args->phdr == dlpi->dlpi_phdr);
TEST_COMPARE (args->phnum, dlpi->dlpi_phnum);
}
return 0;
}
static int
do_test (void)
{
/* Avoid a copy relocation. */
struct r_debug *debug = xdlsym (RTLD_DEFAULT, "_r_debug");
struct link_map *l = (struct link_map *) debug->r_map;
TEST_VERIFY_EXIT (l != NULL);
do
{
printf ("info: checking link map %p (%p) for \"%s\"\n",
l, l->l_phdr, l->l_name);
/* Cause dlerror () to return an error message. */
dlsym (RTLD_DEFAULT, "does-not-exist");
/* Use the extension that link maps are valid dlopen handles. */
const ElfW(Phdr) *phdr;
int phnum = dlinfo (l, RTLD_DI_PHDR, &phdr);
TEST_VERIFY (phnum >= 0);
/* Verify that the error message has been cleared. */
TEST_COMPARE_STRING (dlerror (), NULL);
TEST_VERIFY (phdr == l->l_phdr);
TEST_COMPARE (phnum, l->l_phnum);
/* Check that we can find PT_DYNAMIC among the array. */
{
bool dynamic_found = false;
for (int i = 0; i < phnum; ++i)
if (phdr[i].p_type == PT_DYNAMIC)
{
dynamic_found = true;
TEST_COMPARE ((ElfW(Addr)) l->l_ld, l->l_addr + phdr[i].p_vaddr);
}
TEST_VERIFY (dynamic_found);
}
/* Check that dl_iterate_phdr finds the link map with the same
program headers. */
{
struct dlip_callback_args args =
{
.l = l,
.phdr = phdr,
.phnum = phnum,
.found = false,
};
TEST_COMPARE (dl_iterate_phdr (dlip_callback, &args), 0);
TEST_VERIFY (args.found);
}
if (l->l_prev == NULL)
{
/* This is the executable, so the information is also
available via getauxval. */
TEST_COMPARE_STRING (l->l_name, "");
TEST_VERIFY (phdr == (const ElfW(Phdr) *) getauxval (AT_PHDR));
TEST_COMPARE (phnum, getauxval (AT_PHNUM));
}
l = l->l_next;
}
while (l != NULL);
return 0;
}
#include <support/test-driver.c>

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@ -30,9 +30,9 @@ location @var{arg}, based on @var{request}. The @var{handle} argument
must be a pointer returned by @code{dlopen} or @code{dlmopen}; it must
not have been closed by @code{dlclose}.
On success, @code{dlinfo} returns 0. If there is an error, the function
returns @math{-1}, and @code{dlerror} can be used to obtain a
corresponding error message.
On success, @code{dlinfo} returns 0 for most request types; exceptions
are noted below. If there is an error, the function returns @math{-1},
and @code{dlerror} can be used to obtain a corresponding error message.
The following operations are defined for use with @var{request}:
@ -84,6 +84,15 @@ This request writes the TLS module ID for the shared object @var{handle}
to @code{*@var{arg}}. The argument @var{arg} must be the address of an
object of type @code{size_t}. The module ID is zero if the object
does not have an associated TLS block.
@item RTLD_DI_PHDR
This request writes the address of the program header array to
@code{*@var{arg}}. The argument @var{arg} must be the address of an
object of type @code{const ElfW(Phdr) *} (that is,
@code{const Elf32_Phdr *} or @code{const Elf64_Phdr *}, as appropriate
for the current architecture). For this request, the value returned by
@code{dlinfo} is the number of program headers in the program header
array.
@end vtable
The @code{dlinfo} function is a GNU extension.