[PATCH 1/4] Add an optional offset option to the "symbol-file" command

[Petr Tesarik <ptesarik@suse.cz>]

From: Petr Tesarik <petr@tesarici.cz>

If the main file is relocated at runtime, all symbols are offset by
a fixed amount.  Let the user specify this offset when loading a
symbol file.

gdb/ChangeLog:
2018-06-08  Petr Tesarik  <ptesarik@suse.com>

	* symfile.c (symbol_file_command, symbol_file_add_main_1)
	(_initialize_symfile): Add option "-o" to symbol-file to add an
	offset to each section of the symbol file.

gdb/doc/ChangeLog:
2018-06-08  Petr Tesarik  <ptesarik@suse.com>

	* gdb.texinfo (Files): Document "symbol-file -o offset".

gdb/testsuite/ChangeLog:
2018-06-08  Petr Tesarik  <ptesarik@suse.com>

	* gdb.base/relocate.exp: Add test for "symbol-file -o ".
---
 gdb/ChangeLog                       |  6 ++++++
 gdb/doc/ChangeLog                   |  4 ++++
 gdb/doc/gdb.texinfo                 |  7 ++++++-
 gdb/symfile.c                       | 24 ++++++++++++++++++------
 gdb/testsuite/ChangeLog             |  4 ++++
 gdb/testsuite/gdb.base/relocate.exp | 24 ++++++++++++++++++++++++
 6 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index f0b6b95f7e..27c6ed0a7c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2018-06-08  Petr Tesarik  <ptesarik@suse.com>
+
+	* symfile.c (symbol_file_command, symbol_file_add_main_1)
+	(_initialize_symfile): Add option "-o" to symbol-file to add an
+	offset to each section of the symbol file.
+
 2018-06-07  Pedro Alves  <palves@redhat.com>
 
 	* target.h (target_ops) <beneath>: Now a method.  All references
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 6191e84cc0..319d06a25f 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2018-06-08  Petr Tesarik  <ptesarik@suse.com>
+
+	* gdb.texinfo (Files): Document "symbol-file -o offset".
+
 2018-06-05  Tom Tromey	<tom@tromey.com>
 
 	PR cli/12326:
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4968b374af..9d1c29612b 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -18822,11 +18822,16 @@ if necessary to locate your program.  Omitting @var{filename} means to
 discard information on the executable file.
 
 @kindex symbol-file
-@item symbol-file @r{[} @var{filename} @r{]}
+@item symbol-file @r{[} -o @var{offset} @r{]} @r{[} @var{filename} @r{]}
 Read symbol table information from file @var{filename}.  @code{PATH} is
 searched when necessary.  Use the @code{file} command to get both symbol
 table and program to run from the same file.
 
+If an optional @var{offset} is specified, it is added to the start
+address of each section in the symbol file.  This is useful if the
+program is relocated at runtime, such as the Linux kernel with kASLR
+enabled.
+
 @code{symbol-file} with no argument clears out @value{GDBN} information on your
 program's symbol table.
 
diff --git a/gdb/symfile.c b/gdb/symfile.c
index f8177ea8b1..09344f83d2 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -87,7 +87,7 @@ int readnever_symbol_files;	/* Never read full symbols.  */
 /* Functions this file defines.  */
 
 static void symbol_file_add_main_1 (const char *args, symfile_add_flags add_flags,
-				    objfile_flags flags);
+				    objfile_flags flags, CORE_ADDR reloff);
 
 static const struct sym_fns *find_sym_fns (bfd *);
 
@@ -1225,16 +1225,18 @@ symbol_file_add (const char *name, symfile_add_flags add_flags,
 void
 symbol_file_add_main (const char *args, symfile_add_flags add_flags)
 {
-  symbol_file_add_main_1 (args, add_flags, 0);
+  symbol_file_add_main_1 (args, add_flags, 0, 0);
 }
 
 static void
 symbol_file_add_main_1 (const char *args, symfile_add_flags add_flags,
-			objfile_flags flags)
+			objfile_flags flags, CORE_ADDR reloff)
 {
   add_flags |= current_inferior ()->symfile_flags | SYMFILE_MAINLINE;
 
-  symbol_file_add (args, add_flags, NULL, flags);
+  struct objfile *objfile = symbol_file_add (args, add_flags, NULL, flags);
+  if (reloff != 0)
+    objfile_rebase (objfile, reloff);
 
   /* Getting new symbols may change our opinion about
      what is frameless.  */
@@ -1551,6 +1553,7 @@ symbol_file_command (const char *args, int from_tty)
       symfile_add_flags add_flags = 0;
       char *name = NULL;
       bool stop_processing_options = false;
+      CORE_ADDR offset = 0;
       int idx;
       char *arg;
 
@@ -1571,6 +1574,14 @@ symbol_file_command (const char *args, int from_tty)
 	    flags |= OBJF_READNOW;
 	  else if (strcmp (arg, "-readnever") == 0)
 	    flags |= OBJF_READNEVER;
+	  else if (strcmp (arg, "-o") == 0)
+	    {
+	      arg = built_argv[++idx];
+	      if (arg == NULL)
+		error (_("Missing argument to -o"));
+
+	      offset = parse_and_eval_address (arg);
+	    }
 	  else if (strcmp (arg, "--") == 0)
 	    stop_processing_options = true;
 	  else
@@ -1582,7 +1593,7 @@ symbol_file_command (const char *args, int from_tty)
 
       validate_readnow_readnever (flags);
 
-      symbol_file_add_main_1 (name, add_flags, flags);
+      symbol_file_add_main_1 (name, add_flags, flags, offset);
     }
 }
 
@@ -3774,7 +3785,8 @@ symbolic debug information."
 
   c = add_cmd ("symbol-file", class_files, symbol_file_command, _("\
 Load symbol table from executable file FILE.\n\
-Usage: symbol-file [-readnow | -readnever] FILE\n\
+Usage: symbol-file [-readnow | -readnever] [-o <OFF>] FILE\n\
+OFF is an optional offset which is added to each section address.\n\
 The `file' command can also load symbol tables, as well as setting the file\n\
 to execute.\n" READNOW_READNEVER_HELP), &cmdlist);
   set_cmd_completer (c, filename_completer);
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index eea782f05e..a9e0ec09ff 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2018-06-08  Petr Tesarik  <ptesarik@suse.com>
+
+	* gdb.base/relocate.exp: Add test for "symbol-file -o ".
+
 2018-06-05  Tom Tromey  <tom@tromey.com>
 
 	* gdb.base/default.exp: Update expected "show version" output.
diff --git a/gdb/testsuite/gdb.base/relocate.exp b/gdb/testsuite/gdb.base/relocate.exp
index 89f2fffcd9..77f6a88159 100644
--- a/gdb/testsuite/gdb.base/relocate.exp
+++ b/gdb/testsuite/gdb.base/relocate.exp
@@ -196,6 +196,30 @@ if { "${function_foo_addr}" == "${new_function_foo_addr}" } {
   pass "function foo has a different address"
 }
 
+# Load the object using symbol-file with an offset and check that
+# all addresses are moved by that offset.
+
+set offset 0x10000
+clean_restart
+gdb_test "symbol-file -o $offset $binfile" \
+    "Reading symbols from ${binfile}\.\.\.done\." \
+    "symbol-file with offset"
+
+# Make sure the address of a static variable is moved by offset.
+set new_static_foo_addr [get_var_address static_foo]
+gdb_assert {${new_static_foo_addr} == ${static_foo_addr} + $offset} \
+    "static variable foo is moved by offset"
+
+# Make sure the address of a global variable is moved by offset.
+set new_global_foo_addr [get_var_address global_foo]
+gdb_assert {${new_global_foo_addr} == ${global_foo_addr} + $offset} \
+    "global variable foo is moved by offset"
+
+# Make sure the address of a function is moved by offset.
+set new_function_foo_addr [get_var_address function_foo]
+gdb_assert {${new_function_foo_addr} == ${function_foo_addr} + $offset} \
+    "function foo is moved by offset"
+
 # Now try loading the object as an exec-file; we should be able to print
 # the values of variables after we do this.
 
-- 
2.13.6