dlfcn: Implement the RTLD_DI_PHDR request type for dlinfo
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Commit Message
The information is theoretically available via dl_iterate_phdr as
well, but that approach is very slow if there are many shared
objects.
Tested on i686-linux-gnu and x86_64-linux-gnu. Built with
build-many-glibcs.py.
This patch depends on the previous dlinfo documentation patch.
---
dlfcn/Makefile | 4 ++
dlfcn/dlfcn.h | 7 ++-
dlfcn/dlinfo.c | 13 ++++-
dlfcn/tst-dlinfo-phdr.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++
manual/dynlink.texi | 15 ++++--
5 files changed, 159 insertions(+), 5 deletions(-)
Comments
On 4/20/22 14:53, Florian Weimer via Libc-alpha wrote:
> The information is theoretically available via dl_iterate_phdr as
> well, but that approach is very slow if there are many shared
> objects.
>
> Tested on i686-linux-gnu and x86_64-linux-gnu. Built with
> build-many-glibcs.py.
>
> This patch depends on the previous dlinfo documentation patch.
Pending the manual v3 and commit.
LGTM.
I agree that a dlinfo API for this is useful, and I saw that this helps
resolve a real user request:
https://sourceware.org/pipermail/libc-alpha/2022-March/137096.html
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@rehdat.com>
> ---
> dlfcn/Makefile | 4 ++
> dlfcn/dlfcn.h | 7 ++-
> dlfcn/dlinfo.c | 13 ++++-
> dlfcn/tst-dlinfo-phdr.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++
> manual/dynlink.texi | 15 ++++--
> 5 files changed, 159 insertions(+), 5 deletions(-)
>
> diff --git a/dlfcn/Makefile b/dlfcn/Makefile
> index 6e0a014d99..3255ba02c5 100644
> --- a/dlfcn/Makefile
> +++ b/dlfcn/Makefile
> @@ -73,6 +73,10 @@ tststatic3-ENV = $(tststatic-ENV)
> tststatic4-ENV = $(tststatic-ENV)
> tststatic5-ENV = $(tststatic-ENV)
>
> +tests-internal += \
> + tst-dlinfo-phdr \
> + # tests-internal
OK.
> +
> ifneq (,$(CXX))
> modules-names += bug-atexit3-lib
> else
> diff --git a/dlfcn/dlfcn.h b/dlfcn/dlfcn.h
> index b5cd5c5238..a3af6051d4 100644
> --- a/dlfcn/dlfcn.h
> +++ b/dlfcn/dlfcn.h
> @@ -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
OK. I like that the return is the number of program headers in the array.
> };
>
>
> diff --git a/dlfcn/dlinfo.c b/dlfcn/dlinfo.c
> index fc63c02681..f64ecf59cb 100644
> --- a/dlfcn/dlinfo.c
> +++ b/dlfcn/dlinfo.c
> @@ -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;
OK.
> };
>
> static void
> @@ -40,6 +44,7 @@ dlinfo_doit (void *argsblock)
> {
> case RTLD_DI_CONFIGADDR:
> default:
> + args->result = -1;
OK.
> _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;
OK. Straight forward copy of data we already have.
> + 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;
OK. We need this because result is now returned which is not just -1 or 0.
> }
>
> #ifdef SHARED
> diff --git a/dlfcn/tst-dlinfo-phdr.c b/dlfcn/tst-dlinfo-phdr.c
> new file mode 100644
> index 0000000000..a15a7d48eb
> --- /dev/null
> +++ b/dlfcn/tst-dlinfo-phdr.c
> @@ -0,0 +1,125 @@
> +/* Test for dlinfo (RTLD_DI_PHDR).
OK.
> + 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;
OK. Using tests-internal view of struct link_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);
OK. Call dlinfo with new request.
> + 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);
OK. Compare.
> +
> + /* 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);
OK. Compare.
> + }
> + 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);
OK. Run comparison now with dl_iterate_phdr (after comparison via raw _r_debug values).
> + 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));
OK. Compare now via getauxval.
> + }
> +
> + l = l->l_next;
> + }
> + while (l != NULL);
> +
> + return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/manual/dynlink.texi b/manual/dynlink.texi
> index 6d74fbe2ef..18f78ee002 100644
> --- a/manual/dynlink.texi
> +++ b/manual/dynlink.texi
> @@ -28,9 +28,9 @@ 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.
OK.
>
> The following operations are defined for use with @var{request}:
>
> @@ -82,6 +82,15 @@ 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.
OK.
> @end vtable
> @end deftypefun
>
>
@@ -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
@@ -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
};
@@ -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
new file mode 100644
@@ -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>
@@ -28,9 +28,9 @@ 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}:
@@ -82,6 +82,15 @@ 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
@end deftypefun