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

[Aaron Merey <amerey@redhat.com>]

Hi Simon,

I've fixed the issues you pointed out.  The revised patch is below.

Thanks,
Aaron

From 357ffcc705057b4ed324cc39c2f5159693491fbe Mon Sep 17 00:00:00 2001
From: Aaron Merey <amerey@redhat.com>
Date: Tue, 16 Nov 2021 19:45:44 -0500
Subject: [PATCH 3/3] PR gdb/27570: missing support for debuginfod in
 core_target::build_file_mappings

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

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-ids found in the
core file.  If there is a mismatch, attempt to query debuginfod
for the correct build and print a warning if unsuccessful:

  warning: Build-id of /lib64/libc.so.6 does not match core file.

Also unset the DEBUGINFOD_URLS environment variable in gcore.in
to disable debuginfod when gcore invokes gdb.  Debuginfo is not
needed for core file generation so debuginfod queries will slow
down gcore unnecessarily.
---
 gdb/corelow.c                                 | 27 ++++++++++++
 gdb/debuginfod-support.c                      | 44 +++++++++++++++++++
 gdb/debuginfod-support.h                      | 17 +++++++
 gdb/gcore.in                                  |  3 ++
 gdb/solib.c                                   | 34 ++++++++++++++
 .../gdb.debuginfod/fetch_src_and_symbols.exp  | 22 ++++++++++
 6 files changed, 147 insertions(+)

diff --git a/gdb/corelow.c b/gdb/corelow.c
index d1256a9e99b..8141f815e39 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);
@@ -410,6 +417,26 @@ locate_exec_from_corefile_build_id (bfd *abfd, int from_tty)
   gdb_bfd_ref_ptr execbfd
     = build_id_to_exec_bfd (build_id->size, build_id->data);
 
+  if (execbfd == nullptr)
+    {
+      /* Attempt to query debuginfod for the executable.  */
+      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);
+	}
+    }
+
   if (execbfd != nullptr)
     {
       exec_file_attach (bfd_get_filename (execbfd.get ()), from_tty);
diff --git a/gdb/debuginfod-support.c b/gdb/debuginfod-support.c
index 2e1837da949..c4c593148b6 100644
--- a/gdb/debuginfod-support.c
+++ b/gdb/debuginfod-support.c
@@ -68,6 +68,15 @@ 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);
+}
+
 #define NO_IMPL _("Support for debuginfod is not compiled into GDB.")
 
 #else
@@ -256,6 +265,41 @@ 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)
+{
+  if (!debuginfod_is_enabled ())
+    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 (debuginfod_verbose > 0 && 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
 
 /* Set callback for "set debuginfod enabled".  */
diff --git a/gdb/debuginfod-support.h b/gdb/debuginfod-support.h
index 5e5aab56e74..7815a2f6ede 100644
--- a/gdb/debuginfod-support.h
+++ b/gdb/debuginfod-support.h
@@ -61,4 +61,21 @@ 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 c0beea19d7b..87a3fc0c462 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"
 
@@ -539,6 +541,38 @@ 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 know the build-id of this solib from a core file,
+     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 != nullptr)
+    {
+      bool mismatch = false;
+
+      if (abfd != nullptr && abfd->build_id != nullptr)
+	{
+	  std::string build_id = build_id_to_string (abfd->build_id);
+
+	  if (build_id != build_id_hexstr)
+	    mismatch = true;
+	}
+
+      if (abfd == nullptr || 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 ());
+	  else if (mismatch)
+	    warning (_("Build-id of %ps does not match core file."),
+		     styled_string (file_name_style.style (), 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 757bd201b17..cfe2ae7f7da 100644
--- a/gdb/testsuite/gdb.debuginfod/fetch_src_and_symbols.exp
+++ b/gdb/testsuite/gdb.debuginfod/fetch_src_and_symbols.exp
@@ -63,6 +63,11 @@ 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} {
@@ -114,6 +119,8 @@ proc write_dwarf_file {filename buildid {value 99}} {
     }
 }
 
+set corefile [standard_output_file "corefile"]
+
 proc no_url { } {
     global binfile outputdir debugdir
 
@@ -167,6 +174,16 @@ 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 [file tail $::corefile] gen"
+    file rename -force ${binfile}2 $debugdir
+
+    clean_restart
+    gdb_test "core $::corefile" ".*in ?? ().*" "file [file tail $::corefile]"
 }
 
 proc local_url { } {
@@ -234,6 +251,11 @@ proc local_url { } {
     gdb_test "br main" "Breakpoint 1 at.*file.*"
     gdb_test "l" ".*This program is distributed in the hope.*"
 
+    # gdb should now find the executable file
+    clean_restart
+    gdb_test "core $::corefile" ".*return 0.*" "file [file tail $::corefile]" \
+	"Enable debuginfod?.*" "y"
+
     # gdb should now find the debugaltlink file
     clean_restart
     gdb_test "file ${binfile}_alt.o" \
-- 
2.31.1