commit 91c2e6c3db44297bf4cb3a2e3c40236c5b6a0b23

Author: Florian Weimer <fweimer@redhat.com>

Date:   Fri Apr 29 17:00:53 2022 +0200

    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>

    (cherry picked from commit d056c212130280c0a54d9a4f72170ec621b70ce5)

diff --git a/dlfcn/Makefile b/dlfcn/Makefile

index 6bbfbb8344da05cb..d3965427dabed898 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

+

 ifneq (,$(CXX))

 modules-names += bug-atexit3-lib

 else

diff --git a/dlfcn/dlfcn.h b/dlfcn/dlfcn.h

index 4a3b870a487ea789..24388cfedae4dd67 100644

--- a/dlfcn/dlfcn.h

+++ b/dlfcn/dlfcn.h

@@ -162,7 +162,12 @@ 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

   };

diff --git a/dlfcn/dlinfo.c b/dlfcn/dlinfo.c

index 47d2daa96fa5986f..1842925fb7c594dd 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;

 };

 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

diff --git a/dlfcn/tst-dlinfo-phdr.c b/dlfcn/tst-dlinfo-phdr.c

new file mode 100644

index 0000000000000000..a15a7d48ebd3b976

--- /dev/null

+++ b/dlfcn/tst-dlinfo-phdr.c

@@ -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>

diff --git a/manual/dynlink.texi b/manual/dynlink.texi

index dbf3de11769d8e57..7dcac64889e389fd 100644

--- a/manual/dynlink.texi

+++ b/manual/dynlink.texi

@@ -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.