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

[Petr Tesarik <ptesarik@suse.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.  The Linux kernel with kASLR is one such example.

gdb/ChangeLog:
2018-04-27  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:
2018-04-27  Petr Tesarik  <ptesarik@suse.com>

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

gdb/testsuite/ChangeLog:
2018-04-27  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                       | 28 +++++++++++++++++++++-------
 gdb/testsuite/ChangeLog             |  4 ++++
 gdb/testsuite/gdb.base/relocate.exp | 33 +++++++++++++++++++++++++++++++++
 6 files changed, 74 insertions(+), 8 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cd86be7fb3..56423e7044 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2018-04-27  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.
+
 2018-04-26  Andrzej Kaczmarek  <andrzej.kaczmarek@codecoup.pl>
 
 	PR remote/9665
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 83d48781f9..7a67b80cda 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2018-04-27  Petr Tesarik  <ptesarik@suse.com>
+
+	* gdb.texinfo (Files): Document "symbol-file -o offset".
+
 2018-04-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
 	* gdb.texinfo (Symbols): Mention the fact that "info
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 28f083f96e..56a36d8225 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -18819,11 +18819,16 @@ 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 1e5297ee29..41788f0a67 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 offset);
 
 static const struct sym_fns *find_sym_fns (bfd *);
 
@@ -1222,16 +1222,20 @@ 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 offset)
 {
+  struct objfile *objfile;
+
   add_flags |= current_inferior ()->symfile_flags | SYMFILE_MAINLINE;
 
-  symbol_file_add (args, add_flags, NULL, flags);
+  objfile = symbol_file_add (args, add_flags, NULL, flags);
+  if (offset != 0)
+    objfile_rebase (objfile, offset);
 
   /* Getting new symbols may change our opinion about
      what is frameless.  */
@@ -1548,6 +1552,8 @@ symbol_file_command (const char *args, int from_tty)
       symfile_add_flags add_flags = 0;
       char *name = NULL;
       bool stop_processing_options = false;
+      bool expecting_offset = false;
+      CORE_ADDR offset = 0;
       int idx;
       char *arg;
 
@@ -1559,7 +1565,12 @@ symbol_file_command (const char *args, int from_tty)
 	{
 	  if (stop_processing_options || *arg != '-')
 	    {
-	      if (name == NULL)
+	      if (expecting_offset)
+		{
+		  offset = parse_and_eval_address (arg);
+		  expecting_offset = false;
+		}
+	      else if (name == NULL)
 		name = arg;
 	      else
 		error (_("Unrecognized argument \"%s\""), arg);
@@ -1568,6 +1579,8 @@ 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)
+	    expecting_offset = true;
 	  else if (strcmp (arg, "--") == 0)
 	    stop_processing_options = true;
 	  else
@@ -1579,7 +1592,7 @@ 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);
     }
 }
 
@@ -3772,7 +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 34da102c62..68431cb035 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2018-04-27  Petr Tesarik  <ptesarik@suse.com>
+
+	* gdb.base/relocate.exp: Add test for "symbol-file -o ".
+
 2018-04-26  Pedro Alves  <palves@redhat.com>
 
 	* gdb.base/gnu-ifunc.exp (set-break): Test that GDB resolves
diff --git a/gdb/testsuite/gdb.base/relocate.exp b/gdb/testsuite/gdb.base/relocate.exp
index 89f2fffcd9..4383e79cb2 100644
--- a/gdb/testsuite/gdb.base/relocate.exp
+++ b/gdb/testsuite/gdb.base/relocate.exp
@@ -196,6 +196,39 @@ 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 ${binfile}\.\.\.done\." \
+    "symbol-file with offset"
+
+# Make sure the address of a static variable is moved by offset.
+set new_static_foo_addr [get_var_address static_foo]
+if { "${new_static_foo_addr}" == "${static_foo_addr}" + $offset } {
+  pass "static variable foo is moved by offset"
+} else {
+  fail "static variable foo is moved by offset"
+}
+
+# Make sure the address of a global variable is moved by offset.
+set new_global_foo_addr [get_var_address global_foo]
+if { "${new_global_foo_addr}" == "${global_foo_addr}" + $offset } {
+  pass "global variable foo is moved by offset"
+} else {
+  fail "global variable foo is moved by offset"
+}
+
+# Make sure the address of a functaion is moved by offset.
+set new_function_foo_addr [get_var_address function_foo]
+if { "${new_function_foo_addr}" == "${function_foo_addr}" + $offset } {
+  pass "function foo is moved by offset"
+} else {
+  fail "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