debuginfod: add client context

Add a mandatory debuginfod_begin()/_end() call pair to manage a client
object that represents persistent but non-global state.  From libdwfl,
dlopen the debuginfod.so client library early on.  This hopefully
makes sure that the code (and the libcurl.so dependency) is loaded
before the program goes into multi-threaded mode.

Signed-off-by: Mark Wielaard <mark@klomp.org>

6 files changed, 160 insertions, 53 deletions

diff --git a/libdwfl/Makefile.am b/libdwfl/Makefile.am
index 29046e9e..47bd62a5 100644
--- a/libdwfl/Makefile.am
+++ b/libdwfl/Makefile.am
@@ -70,7 +70,7 @@ libdwfl_a_SOURCES = dwfl_begin.c dwfl_end.c dwfl_error.c dwfl_version.c \
 		    link_map.c core-file.c open.c image-header.c \
 		    dwfl_frame.c frame_unwind.c dwfl_frame_pc.c \
 		    linux-pid-attach.c linux-core-attach.c dwfl_frame_regs.c \
-		    gzip.c
+		    gzip.c debuginfod-client.c
 
 if BZLIB
 libdwfl_a_SOURCES += bzip2.c
diff --git a/libdwfl/debuginfod-client.c b/libdwfl/debuginfod-client.c
new file mode 100644
index 00000000..ee604ad9
--- /dev/null
+++ b/libdwfl/debuginfod-client.c
@@ -0,0 +1,131 @@
+/* Try to get an ELF or debug file through the debuginfod.
+   Copyright (C) 2019 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils 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
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "libdwflP.h"
+#include <dlfcn.h>
+
+static __typeof__ (debuginfod_begin) *fp_debuginfod_begin;
+static __typeof__ (debuginfod_find_executable) *fp_debuginfod_find_executable;
+static __typeof__ (debuginfod_find_debuginfo) *fp_debuginfod_find_debuginfo;
+static __typeof__ (debuginfod_end) *fp_debuginfod_end;
+
+/* NB: this is slightly thread-unsafe */
+
+static debuginfod_client *
+get_client (Dwfl *dwfl)
+{
+  if (dwfl->debuginfod != NULL)
+    return dwfl->debuginfod;
+
+  if (fp_debuginfod_begin != NULL)
+    {
+      dwfl->debuginfod = (*fp_debuginfod_begin) ();
+      return dwfl->debuginfod;
+    }
+
+  return NULL;
+}
+
+int
+__libdwfl_debuginfod_find_executable (Dwfl *dwfl,
+				      const unsigned char *build_id_bits,
+				      size_t build_id_len)
+{
+  int fd = -1;
+  if (build_id_len > 0)
+    {
+      debuginfod_client *c = get_client (dwfl);
+      if (c != NULL)
+	fd = (*fp_debuginfod_find_executable) (c, build_id_bits,
+					       build_id_len, NULL);
+    }
+
+  return fd;
+}
+
+int
+__libdwfl_debuginfod_find_debuginfo (Dwfl *dwfl,
+				     const unsigned char *build_id_bits,
+				     size_t build_id_len)
+{
+  int fd = -1;
+  if (build_id_len > 0)
+    {
+      debuginfod_client *c = get_client (dwfl);
+      if (c != NULL)
+	fd = (*fp_debuginfod_find_debuginfo) (c, build_id_bits,
+					      build_id_len, NULL);
+    }
+
+  return fd;
+}
+
+void
+__libdwfl_debuginfod_end (debuginfod_client *c)
+{
+  if (c != NULL)
+    (*fp_debuginfod_end) (c);
+}
+
+/* Try to get the libdebuginfod library functions to make sure
+   everything is initialized early.  */
+void __attribute__ ((constructor))
+__libdwfl_debuginfod_init (void)
+{
+  void *debuginfod_so = dlopen("libdebuginfod-" VERSION ".so", RTLD_LAZY);
+
+  if (debuginfod_so == NULL)
+    debuginfod_so = dlopen("libdebuginfod.so", RTLD_LAZY);
+
+  if (debuginfod_so != NULL)
+    {
+      fp_debuginfod_begin = dlsym (debuginfod_so, "debuginfod_begin");
+      fp_debuginfod_find_executable = dlsym (debuginfod_so,
+					     "debuginfod_find_executable");
+      fp_debuginfod_find_debuginfo = dlsym (debuginfod_so,
+					    "debuginfod_find_debuginfo");
+      fp_debuginfod_end = dlsym (debuginfod_so, "debuginfod_end");
+
+      /* We either get them all, or we get none.  */
+      if (fp_debuginfod_begin == NULL
+	  || fp_debuginfod_find_executable == NULL
+	  || fp_debuginfod_find_debuginfo == NULL
+	  || fp_debuginfod_end == NULL)
+	{
+	  fp_debuginfod_begin = NULL;
+	  fp_debuginfod_find_executable = NULL;
+	  fp_debuginfod_find_debuginfo = NULL;
+	  fp_debuginfod_end = NULL;
+	  dlclose (debuginfod_so);
+	}
+    }
+}
diff --git a/libdwfl/dwfl_build_id_find_elf.c b/libdwfl/dwfl_build_id_find_elf.c
index b775f50a..4e56143f 100644
--- a/libdwfl/dwfl_build_id_find_elf.c
+++ b/libdwfl/dwfl_build_id_find_elf.c
@@ -34,9 +34,7 @@
 #include <inttypes.h>
 #include <fcntl.h>
 #include <unistd.h>
-#include <dlfcn.h>
 #include "system.h"
-#include "debuginfod.h"
 
 
 int
@@ -189,31 +187,15 @@ dwfl_build_id_find_elf (Dwfl_Module *mod,
       free (*file_name);
       *file_name = NULL;
     }
-  else {
-    /* NB: this is slightly thread-unsafe */
-    static __typeof__ (debuginfod_find_executable) *fp_debuginfod_find_executable;
-
-    if (fp_debuginfod_find_executable == NULL)
-      {
-        void *debuginfod_so = dlopen("libdebuginfod-" VERSION ".so", RTLD_LAZY);
-        if (debuginfod_so == NULL)
-          debuginfod_so = dlopen("libdebuginfod.so", RTLD_LAZY);
-        if (debuginfod_so != NULL)
-          fp_debuginfod_find_executable = dlsym (debuginfod_so, "debuginfod_find_executable");
-        if (fp_debuginfod_find_executable == NULL)
-          fp_debuginfod_find_executable = (void *) -1; /* never try again */
-      }
-
-    if (fp_debuginfod_find_executable != NULL && fp_debuginfod_find_executable != (void *) -1)
-      {
-        /* If all else fails and a build-id is available, query the
-           debuginfo-server if enabled.  */
-        if (fd < 0 && mod->build_id_len > 0)
-          fd = (*fp_debuginfod_find_executable) (mod->build_id_bits,
-                                                mod->build_id_len,
-                                                NULL);
-      }
-  }
+  else
+    {
+      /* If all else fails and a build-id is available, query the
+	 debuginfo-server if enabled.  */
+      if (fd < 0 && mod->build_id_len > 0)
+	fd = __libdwfl_debuginfod_find_executable (mod->dwfl,
+						   mod->build_id_bits,
+						   mod->build_id_len);
+    }
 
   if (fd < 0 && errno == 0 && mod->build_id_len > 0)
     /* Setting this with no file yet loaded is a marker that
diff --git a/libdwfl/dwfl_end.c b/libdwfl/dwfl_end.c
index 74ee9e07..4f6c722a 100644
--- a/libdwfl/dwfl_end.c
+++ b/libdwfl/dwfl_end.c
@@ -39,6 +39,8 @@ dwfl_end (Dwfl *dwfl)
   if (dwfl == NULL)
     return;
 
+  __libdwfl_debuginfod_end (dwfl->debuginfod);
+
   if (dwfl->process)
     __libdwfl_process_free (dwfl->process);
 
diff --git a/libdwfl/find-debuginfo.c b/libdwfl/find-debuginfo.c
index ffc07f92..40857645 100644
--- a/libdwfl/find-debuginfo.c
+++ b/libdwfl/find-debuginfo.c
@@ -31,11 +31,9 @@
 #endif
 
 #include "libdwflP.h"
-#include "debuginfod.h"
 #include <stdio.h>
 #include <fcntl.h>
 #include <unistd.h>
-#include <dlfcn.h>
 #include <sys/stat.h>
 #include "system.h"
 
@@ -400,29 +398,8 @@ dwfl_standard_find_debuginfo (Dwfl_Module *mod,
       free (canon);
     }
 
-  {
-    /* NB: this is slightly thread-unsafe */
-    static __typeof__ (debuginfod_find_debuginfo) *fp_debuginfod_find_debuginfo;
-
-    if (fp_debuginfod_find_debuginfo == NULL)
-      {
-        void *debuginfod_so = dlopen("libdebuginfod-" VERSION ".so", RTLD_LAZY);
-        if (debuginfod_so == NULL)
-          debuginfod_so = dlopen("libdebuginfod.so", RTLD_LAZY);
-        if (debuginfod_so != NULL)
-          fp_debuginfod_find_debuginfo = dlsym (debuginfod_so, "debuginfod_find_debuginfo");
-        if (fp_debuginfod_find_debuginfo == NULL)
-          fp_debuginfod_find_debuginfo = (void *) -1; /* never try again */
-      }
-
-    if (fp_debuginfod_find_debuginfo != NULL && fp_debuginfod_find_debuginfo != (void *) -1)
-      {
-        /* If all else fails and a build-id is available, query the
-           debuginfo-server if enabled.  */
-        if (fd < 0 && bits_len > 0)
-          fd = (*fp_debuginfod_find_debuginfo) (bits, bits_len, NULL);
-      }
-  }
+  if (fd < 0 && bits_len > 0)
+    fd = __libdwfl_debuginfod_find_debuginfo (mod->dwfl, bits, bits_len);
 
   return fd;
 }
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 6b2d4867..f631f946 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -40,6 +40,7 @@
 
 #include "../libdw/libdwP.h"	/* We need its INTDECLs.  */
 #include "../libdwelf/libdwelfP.h"
+#include "../debuginfod/debuginfod.h"
 
 typedef struct Dwfl_Process Dwfl_Process;
 
@@ -114,6 +115,7 @@ struct Dwfl_User_Core
 struct Dwfl
 {
   const Dwfl_Callbacks *callbacks;
+  debuginfod_client *debuginfod;
 
   Dwfl_Module *modulelist;    /* List in order used by full traversals.  */
 
@@ -634,6 +636,19 @@ extern Dwfl_Error __libdw_open_elf (int fd, Elf **elfp) internal_function;
 extern bool __libdwfl_dynamic_vaddr_get (Elf *elf, GElf_Addr *vaddrp)
   internal_function;
 
+/* Internal interface to libdebuginfod (if installed).  */
+int
+__libdwfl_debuginfod_find_executable (Dwfl *dwfl,
+				      const unsigned char *build_id_bits,
+				      size_t build_id_len);
+int
+__libdwfl_debuginfod_find_debuginfo (Dwfl *dwfl,
+				     const unsigned char *build_id_bits,
+				     size_t build_id_len);
+void
+__libdwfl_debuginfod_end (debuginfod_client *c);
+
+
 /* These are working nicely for --core, but are not ready to be
    exported interfaces quite yet.  */