[PATCH 3/3] PR gdb/27570: missing support for debuginfod in core_target::build_file_mappings

[Aaron Merey <amerey@redhat.com>]

Add debuginfod support to core_target::build_file_mappings and
locate_exec_from_corefile_build_id to enable the downloading of
missing core file executables and shared libraries.

Also add debuginfod support to solib_map_sections so that previously
downloaded shared libraries can be retrieved from the debuginfod
cache.

When core file shared libraries are found locally, verify
that their build-ids match the corresponding build-id found in
the core file.  If there is a mismatch, print a warning and attempt
to query debuginfod for the correct build of the shared library:

warning: Build-id of /lib64/libc.so.6 does not match core file.
Downloading XY.Z MB executable for /lib64/libc.so.6
---
 gdb/corelow.c                                 | 33 +++++++++++++
 gdb/debuginfod-support.c                      | 46 +++++++++++++++++++
 gdb/debuginfod-support.h                      | 16 +++++++
 gdb/gcore.in                                  |  3 ++
 gdb/solib.c                                   | 35 ++++++++++++++
 .../gdb.debuginfod/fetch_src_and_symbols.exp  | 25 +++++++++-
 6 files changed, 156 insertions(+), 2 deletions(-)

diff --git a/gdb/corelow.c b/gdb/corelow.c
index 97eadceed84..2c9ea1044b7 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -46,6 +46,8 @@
 #include "gdbsupport/filestuff.h"
 #include "build-id.h"
 #include "gdbsupport/pathstuff.h"
+#include "gdbsupport/scoped_fd.h"
+#include "debuginfod-support.h"
 #include <unordered_map>
 #include <unordered_set>
 #include "gdbcmd.h"
@@ -229,6 +231,11 @@ core_target::build_file_mappings ()
 	       canonical) pathname will be provided.  */
 	    gdb::unique_xmalloc_ptr<char> expanded_fname
 	      = exec_file_find (filename, NULL);
+
+	    if (expanded_fname == nullptr && build_id != nullptr)
+	      debuginfod_exec_query (build_id->data, build_id->size,
+				     filename, &expanded_fname);
+
 	    if (expanded_fname == nullptr)
 	      {
 		m_core_unavailable_mappings.emplace_back (start, end - start);
@@ -416,6 +423,32 @@ locate_exec_from_corefile_build_id (bfd *abfd, int from_tty)
       symbol_file_add_main (bfd_get_filename (execbfd.get ()),
 			    symfile_add_flag (from_tty ? SYMFILE_VERBOSE : 0));
     }
+  else
+    {
+      gdb::unique_xmalloc_ptr<char> execpath;
+      scoped_fd fd = debuginfod_exec_query (build_id->data, build_id->size,
+					    abfd->filename, &execpath);
+
+      if (fd.get () >= 0)
+	{
+	  execbfd = gdb_bfd_open (execpath.get (), gnutarget);
+
+	  if (execbfd == nullptr)
+	    warning (_("File \"%s\" from debuginfod cannot be opened as bfd"),
+		     execpath.get ());
+	  else if (!build_id_verify (execbfd.get (), build_id->size,
+				     build_id->data))
+	    execbfd.reset (nullptr);
+	  else
+	    {
+	      /* Successful download */
+	      exec_file_attach (execpath.get (), from_tty);
+	      symbol_file_add_main (execpath.get (),
+				    symfile_add_flag (from_tty ?
+						      SYMFILE_VERBOSE : 0));
+	    }
+	}
+    }
 }
 
 /* See gdbcore.h.  */
diff --git a/gdb/debuginfod-support.c b/gdb/debuginfod-support.c
index 2d626e335a0..04b39b57f6f 100644
--- a/gdb/debuginfod-support.c
+++ b/gdb/debuginfod-support.c
@@ -41,6 +41,16 @@ debuginfod_debuginfo_query (const unsigned char *build_id,
 {
   return scoped_fd (-ENOSYS);
 }
+
+scoped_fd
+debuginfod_exec_query (const unsigned char *build_id,
+		       int build_id_len,
+		       const char *filename,
+		       gdb::unique_xmalloc_ptr<char> *destname)
+{
+  return scoped_fd (-ENOSYS);
+}
+
 #else
 #include <elfutils/debuginfod.h>
 
@@ -194,4 +204,40 @@ debuginfod_debuginfo_query (const unsigned char *build_id,
 
   return fd;
 }
+
+/* See debuginfod-support.h  */
+
+scoped_fd
+debuginfod_exec_query (const unsigned char *build_id,
+		       int build_id_len,
+		       const char *filename,
+		       gdb::unique_xmalloc_ptr<char> *destname)
+{
+  const char *urls_env_var = getenv (DEBUGINFOD_URLS_ENV_VAR);
+  if (urls_env_var == NULL || urls_env_var[0] == '\0')
+    return scoped_fd (-ENOSYS);
+
+  debuginfod_client *c = get_debuginfod_client ();
+
+  if (c == nullptr)
+    return scoped_fd (-ENOMEM);
+
+  char *dname = nullptr;
+  user_data data ("executable for", filename);
+
+  debuginfod_set_user_data (c, &data);
+  scoped_fd fd (debuginfod_find_executable (c, build_id, build_id_len, &dname));
+  debuginfod_set_user_data (c, nullptr);
+
+  if (fd.get () < 0 && fd.get () != -ENOENT)
+    printf_filtered (_("Download failed: %s. " \
+		       "Continuing without executable for %ps.\n"),
+		     safe_strerror (-fd.get ()),
+		     styled_string (file_name_style.style (),  filename));
+
+  if (fd.get () >= 0)
+    destname->reset (dname);
+
+  return fd;
+}
 #endif
diff --git a/gdb/debuginfod-support.h b/gdb/debuginfod-support.h
index 5e5aab56e74..c29a07d2abe 100644
--- a/gdb/debuginfod-support.h
+++ b/gdb/debuginfod-support.h
@@ -61,4 +61,20 @@ debuginfod_debuginfo_query (const unsigned char *build_id,
 			    const char *filename,
 			    gdb::unique_xmalloc_ptr<char> *destname);
 
+/* Query debuginfod servers for an executable file with BUILD_ID.
+   BUILD_ID can be given as a binary blob or a null-terminated string.
+   If given as a binary blob, BUILD_ID_LEN should be the number of bytes.
+   If given as a null-terminated string, BUILD_ID_LEN should be 0.
+
+   FILENAME should be the name or path associated with the executable.
+   It is used for printing messages to the user.
+
+   If the file is successfully retrieved, its path on the local machine
+   is stored in DESTNAME.  If GDB is not built with debuginfod, this
+   function returns -ENOSYS.  */
+
+extern scoped_fd debuginfod_exec_query (const unsigned char *build_id,
+					int build_id_len,
+					const char *filename,
+					gdb::unique_xmalloc_ptr<char> *destname);
 #endif /* DEBUGINFOD_SUPPORT_H */
diff --git a/gdb/gcore.in b/gdb/gcore.in
index 24354a79e27..25b24c3cd3d 100644
--- a/gdb/gcore.in
+++ b/gdb/gcore.in
@@ -89,6 +89,9 @@ if [ ! -f "$binary_path/@GDB_TRANSFORM_NAME@" ]; then
   exit 1
 fi
 
+# Prevent unnecessary debuginfod queries during core file generation.
+unset DEBUGINFOD_URLS
+
 # Initialise return code.
 rc=0
 
diff --git a/gdb/solib.c b/gdb/solib.c
index 8b92cf7db53..3a7bf59e64a 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -49,6 +49,8 @@
 #include "filesystem.h"
 #include "gdb_bfd.h"
 #include "gdbsupport/filestuff.h"
+#include "gdbsupport/scoped_fd.h"
+#include "debuginfod-support.h"
 #include "source.h"
 #include "cli/cli-style.h"
 
@@ -538,6 +540,39 @@ solib_map_sections (struct so_list *so)
 
   gdb::unique_xmalloc_ptr<char> filename (tilde_expand (so->so_name));
   gdb_bfd_ref_ptr abfd (ops->bfd_open (filename.get ()));
+  const char *build_id_hexstr =
+    current_program_space->get_cbfd_soname_build_id (so->so_name);
+
+  /* If we already have core file build-id information for this solib,
+     verify it matches abfd's build-id.  If there is a mismatch or
+     the solib wasn't found, attempt to query debuginfod for
+     the correct solib.  */
+  if (build_id_hexstr != NULL)
+    {
+      bool mismatch = false;
+
+      if (abfd != NULL && abfd->build_id != NULL)
+	{
+	  std::string build_id = build_id_to_string (abfd->build_id);
+	  if (build_id != build_id_hexstr)
+	    {
+	      warning (_("Build-id of %ps does not match core file."),
+		       styled_string (file_name_style.style (),
+				      filename.get ()));
+	      mismatch = true;
+	    }
+	}
+
+      if (abfd == NULL || mismatch)
+	{
+	  scoped_fd fd = debuginfod_exec_query ((const unsigned char*)
+						build_id_hexstr,
+						0, so->so_name, &filename);
+
+	  if (fd.get () >= 0)
+	    abfd = ops->bfd_open (filename.get ());
+	}
+    }
 
   if (abfd == NULL)
     return 0;
diff --git a/gdb/testsuite/gdb.debuginfod/fetch_src_and_symbols.exp b/gdb/testsuite/gdb.debuginfod/fetch_src_and_symbols.exp
index 81d4791eb6d..79ec4e6f853 100644
--- a/gdb/testsuite/gdb.debuginfod/fetch_src_and_symbols.exp
+++ b/gdb/testsuite/gdb.debuginfod/fetch_src_and_symbols.exp
@@ -58,6 +58,11 @@ if { [gdb_compile "$sourcetmp" "$binfile" executable {debug}] != "" } {
     return -1
 }
 
+if { [gdb_compile "$sourcetmp" "${binfile}2" executable {debug}] != "" } {
+    fail "compile"
+    return -1
+}
+
 # Write some assembly that just has a .gnu_debugaltlink section.
 # Copied from testsuite/gdb.dwarf2/dwzbuildid.exp.
 proc write_just_debugaltlink {filename dwzname buildid} {
@@ -109,8 +114,10 @@ proc write_dwarf_file {filename buildid {value 99}} {
     }
 }
 
+set corefile "corefile"
+
 proc no_url { } {
-    global binfile outputdir debugdir
+    global binfile corefile outputdir debugdir
 
     setenv DEBUGINFOD_URLS ""
 
@@ -162,10 +169,20 @@ proc no_url { } {
     gdb_test "file ${binfile}_alt.o" \
 	".*could not find '.gnu_debugaltlink'.*" \
 	"file [file tail ${binfile}_alt.o]"
+
+    # Generate a core file and test that gdb cannot find the executable
+    clean_restart ${binfile}2
+    gdb_test "start" "Temporary breakpoint.*"
+    gdb_test "generate-core-file $corefile" \
+	"Saved corefile $corefile"
+    file rename -force ${binfile}2 $debugdir
+
+    clean_restart
+    gdb_test "core $corefile" ".*in ?? ().*"
 }
 
 proc local_url { } {
-    global binfile outputdir db debugdir
+    global binfile corefile outputdir db debugdir
 
     # Find an unused port
     set port 7999
@@ -228,6 +245,10 @@ proc local_url { } {
     gdb_test "file ${binfile}_alt.o" \
 	".*Reading symbols from ${binfile}_alt.o\.\.\.*" \
 	"file [file tail ${binfile}_alt.o]"
+
+    # gdb should now find the executable file
+    clean_restart
+    gdb_test "core $corefile" ".*return 0.*"
 }
 
 set envlist \
-- 
2.31.1