debuginfod 1/2: client side

Introduce the debuginfod/ subdirectory, containing the client for a
new debuginfo-over-http service, in shared-library and command-line
forms.  Two functions in libdwfl make calls into the client library to
fetch elf/dwarf files by buildid, as a fallback.  Instead of normal
dynamic linking (thus pulling in a variety of curl dependencies),
the libdwfl hooks use dlopen/dlsym.  Server & tests coming in patch 2.

Signed-off-by: Aaron Merey <amerey@redhat.com>
Signed-off-by: Frank Ch. Eigler <fche@redhat.com>

4 files changed, 67 insertions, 5 deletions

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 07a1e8df..b8222189 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,9 @@
+2019-10-28  Aaron Merey  <amerey@redhat.com>
+
+	* dwfl_build_id_find_elf.c (dwfl_build_id_find_elf): Call debuginfod
+	client functions via dlopen to look for elf/dwarf files as fallback.
+	* find-debuginfo.c (dwfl_standard_find_debuginfo): Ditto.
+
 2019-10-07  Omar Sandoval  <osandov@fb.com>
 
 	* dwfl_frame.c (dwfl_getthreads): Get rid of unnecessary
diff --git a/libdwfl/Makefile.am b/libdwfl/Makefile.am
index 89ca92ed..29046e9e 100644
--- a/libdwfl/Makefile.am
+++ b/libdwfl/Makefile.am
@@ -31,7 +31,7 @@
 ##
 include $(top_srcdir)/config/eu.am
 AM_CPPFLAGS += -I$(srcdir) -I$(srcdir)/../libelf -I$(srcdir)/../libebl \
-	   -I$(srcdir)/../libdw -I$(srcdir)/../libdwelf
+	   -I$(srcdir)/../libdw -I$(srcdir)/../libdwelf -I$(srcdir)/../debuginfod
 VERSION = 1
 
 noinst_LIBRARIES = libdwfl.a
@@ -39,6 +39,7 @@ noinst_LIBRARIES += libdwfl_pic.a
 
 pkginclude_HEADERS = libdwfl.h
 
+
 libdwfl_a_SOURCES = dwfl_begin.c dwfl_end.c dwfl_error.c dwfl_version.c \
 		    dwfl_module.c dwfl_report_elf.c relocate.c \
 		    dwfl_module_build_id.c dwfl_module_report_build_id.c \
diff --git a/libdwfl/dwfl_build_id_find_elf.c b/libdwfl/dwfl_build_id_find_elf.c
index cc6c3f62..b775f50a 100644
--- a/libdwfl/dwfl_build_id_find_elf.c
+++ b/libdwfl/dwfl_build_id_find_elf.c
@@ -1,5 +1,5 @@
 /* Find an ELF file for a module from its build ID.
-   Copyright (C) 2007-2010, 2014, 2015 Red Hat, Inc.
+   Copyright (C) 2007-2010, 2014, 2015, 2019 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -34,7 +34,9 @@
 #include <inttypes.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <dlfcn.h>
 #include "system.h"
+#include "debuginfod.h"
 
 
 int
@@ -187,7 +189,33 @@ dwfl_build_id_find_elf (Dwfl_Module *mod,
       free (*file_name);
       *file_name = NULL;
     }
-  else if (errno == 0 && mod->build_id_len > 0)
+  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);
+      }
+  }
+
+  if (fd < 0 && errno == 0 && mod->build_id_len > 0)
     /* Setting this with no file yet loaded is a marker that
        the build ID is authoritative even if we also know a
        putative *FILE_NAME.  */
diff --git a/libdwfl/find-debuginfo.c b/libdwfl/find-debuginfo.c
index 9267788d..ffc07f92 100644
--- a/libdwfl/find-debuginfo.c
+++ b/libdwfl/find-debuginfo.c
@@ -1,5 +1,5 @@
 /* Standard find_debuginfo callback for libdwfl.
-   Copyright (C) 2005-2010, 2014, 2015 Red Hat, Inc.
+   Copyright (C) 2005-2010, 2014, 2015, 2019 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -31,9 +31,11 @@
 #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"
 
@@ -359,7 +361,8 @@ dwfl_standard_find_debuginfo (Dwfl_Module *mod,
      other than just by finding nothing, that's all we do.  */
   const unsigned char *bits;
   GElf_Addr vaddr;
-  if (INTUSE(dwfl_module_build_id) (mod, &bits, &vaddr) > 0)
+  int bits_len;
+  if ((bits_len = INTUSE(dwfl_module_build_id) (mod, &bits, &vaddr)) > 0)
     {
       /* Dropping most arguments means we cannot rely on them in
 	 dwfl_build_id_find_debuginfo.  But leave it that way since
@@ -397,6 +400,30 @@ 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);
+      }
+  }
+
   return fd;
 }
 INTDEF (dwfl_standard_find_debuginfo)