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[binutils-gdb] set varsize-limit: New GDB setting for maximum dynamic object size


https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=3fcded8f30b6b0c1930d4f82914476315027aa2e

commit 3fcded8f30b6b0c1930d4f82914476315027aa2e
Author: Joel Brobecker <brobecker@adacore.com>
Date:   Tue Mar 27 09:17:45 2018 -0500

    set varsize-limit: New GDB setting for maximum dynamic object size
    
    This is a command we somehow forgot to contribute at the time the Ada
    language was first contributed to the FSF. This command allows
    the user to change the maximum size we allow when reading memory
    from dynamic objects (the default is 65536 bytes).
    
    At the moment, this limit is only used by Ada, and so the implementation
    is kept inside ada-lang.c. However, it is conceivable that other language
    might want to use it also to handle the same kind of issues; for instance,
    this might be useful when handling dynamic types in C. So the name
    of the setting was made language-neutral, to allow for this.
    
    Note that an alias for "set var" needs to be introduced as well.
    We are not adding a test for that, since this is a feature that is
    already exercized by numerous existing tests.
    
    gdb/ChangeLog
    
            * NEWS: Add entry describing new "set|show varsize-limit" command.
            * ada-lang.c (_initialize_ada_language): Add "set/show varsize-limit"
            command.
            * printcmd.c (_initialize_printcmd): Add "set var" alias of
            "set variable".
    
    gdb/doc/ChangeLog:
    
            * gdb.texinfo (Ada Settings): New subsubsection.
    
    gdb/testsuite/ChangeLog:
    
            * gdb.ada/varsize_limit: New testcase.
    
    Tested on x86_64-linux.

Diff:
---
 gdb/ChangeLog                                    |  8 +++++
 gdb/NEWS                                         |  5 ++++
 gdb/ada-lang.c                                   |  7 +++++
 gdb/doc/ChangeLog                                |  4 +++
 gdb/doc/gdb.texinfo                              | 32 ++++++++++++++++++++
 gdb/printcmd.c                                   |  1 +
 gdb/testsuite/ChangeLog                          |  4 +++
 gdb/testsuite/gdb.ada/varsize_limit.exp          | 38 ++++++++++++++++++++++++
 gdb/testsuite/gdb.ada/varsize_limit/pck.adb      | 25 ++++++++++++++++
 gdb/testsuite/gdb.ada/varsize_limit/pck.ads      | 20 +++++++++++++
 gdb/testsuite/gdb.ada/varsize_limit/vsizelim.adb | 23 ++++++++++++++
 11 files changed, 167 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index e78bfcb..79c981d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2018-03-27  Joel Brobecker  <brobecker@adacore.com>
+
+	* NEWS: Add entry describing new "set|show varsize-limit" command.
+	* ada-lang.c (_initialize_ada_language): Add "set/show varsize-limit"
+	command.
+	* printcmd.c (_initialize_printcmd): Add "set var" alias of
+	"set variable".
+
 2018-03-27  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* Makefile.in (COMMON_SFILES): Add dwarf-index-common.c and
diff --git a/gdb/NEWS b/gdb/NEWS
index 3679090..ef0313d 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -12,6 +12,11 @@ set debug fbsd-nat
 show debug fbsd-nat
   Control display of debugging info regarding the FreeBSD native target.
 
+set|show varsize-limit
+  This new setting allows the user to control the maximum size of Ada
+  objects being printed when those objects have a variable type,
+  instead of that maximum size being hardcoded to 65536 bytes.
+
 * New targets
 
 RiscV ELF			riscv*-*-elf
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 191b7e4..505d059 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -14689,6 +14689,13 @@ With an argument, catch only exceptions with the given name."),
 		     CATCH_TEMPORARY);
 
   varsize_limit = 65536;
+  add_setshow_uinteger_cmd ("varsize-limit", class_support,
+			    &varsize_limit, _("\
+Set the maximum number of bytes allowed in a variable-size object."), _("\
+Show the maximum number of bytes allowed in a variable-size object."), _("\
+Attempts to access an object whose size is not a compile-time constant\n\
+and exceeds this limit will cause an error."),
+			    NULL, NULL, &setlist, &showlist);
 
   add_info ("exceptions", info_exceptions_command,
 	    _("\
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 4da77de..f11fa0c 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,7 @@
+2018-03-27  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.texinfo (Ada Settings): New subsubsection.
+
 2018-03-26  Tom Tromey  <tom@tromey.com>
 
 	PR backtrace/15582:
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d37b107..bd20b39 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -16272,6 +16272,7 @@ to be difficult.
 * Ada Tasks and Core Files::    Tasking Support when Debugging Core Files
 * Ravenscar Profile::           Tasking Support when using the Ravenscar
                                    Profile
+* Ada Settings::                New settable GDB parameters for Ada.
 * Ada Glitches::                Known peculiarities of Ada mode.
 @end menu
 
@@ -16927,6 +16928,37 @@ using the Ravenscar Profile.
 
 @end table
 
+@node Ada Settings
+@subsubsection Ada Settings
+@cindex Ada settings
+
+@table @code
+@kindex set varsize-limit
+@item set varsize-limit @var{size}
+Prevent @value{GDBN} from attempting to evaluate objects whose size
+is above the given limit (@var{size}) when those sizes are computed
+from run-time quantities.  This is typically the case when the object
+has a variable size, such as an array whose bounds are not known at
+compile time for example.  Setting @var{size} to @code{unlimited}
+removes the size limitation.  By default, the limit is about 65KB.
+
+The purpose of having such a limit is to prevent @value{GDBN} from
+trying to grab enormous chunks of virtual memory when asked to evaluate
+a quantity whose bounds have been corrupted or have not yet been fully
+initialized.  The limit applies to the results of some subexpressions
+as well as to complete expressions.  For example, an expression denoting
+a simple integer component, such as @code{x.y.z}, may fail if the size of
+@code{x.y} is variable and exceeds @code{size}.  On the other hand,
+@value{GDBN} is sometimes clever; the expression @code{A(i)}, where
+@code{A} is an array variable with non-constant size, will generally
+succeed regardless of the bounds on @code{A}, as long as the component
+size is less than @var{size}.
+
+@kindex show varsize-limit
+@item show varsize-limit
+Show the limit on types whose size is determined by run-time quantities.
+@end table
+
 @node Ada Glitches
 @subsubsection Known Peculiarities of Ada Mode
 @cindex Ada, problems
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index dd81d8f..58bdac6 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -2737,6 +2737,7 @@ with $), a register (a few standard names starting with $), or an actual\n\
 variable in the program being debugged.  EXP is any valid expression.\n\
 This may usually be abbreviated to simply \"set\"."),
 	   &setlist);
+  add_alias_cmd ("var", "variable", class_vars, 0, &setlist);
 
   c = add_com ("print", class_vars, print_command, _("\
 Print value of expression EXP.\n\
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 8dffab5..806744d 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,9 @@
 2018-03-27  Joel Brobecker  <brobecker@adacore.com>
 
+	* gdb.ada/varsize_limit: New testcase.
+
+2018-03-27  Joel Brobecker  <brobecker@adacore.com>
+
 	* gdb.ada/maint_with_ada.exp: Remove PR gdb/22670 setup_kfail.
 
 	* gdb.ada/notcplusplus: New testcase.
diff --git a/gdb/testsuite/gdb.ada/varsize_limit.exp b/gdb/testsuite/gdb.ada/varsize_limit.exp
new file mode 100644
index 0000000..b201755
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/varsize_limit.exp
@@ -0,0 +1,38 @@
+# Copyright 2018 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib "ada.exp"
+
+standard_ada_testfile vsizelim
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug ]] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "STOP" ${testdir}/vsizelim.adb]
+if ![runto "vsizelim.adb:$bp_location" ] then {
+  perror "Couldn't run ${testfile}"
+  return
+}
+
+gdb_test_no_output "set varsize-limit 16"
+
+gdb_test "print small" " = \"1234567890\""
+
+gdb_test "print larger" "object size is larger than varsize-limit.*"
+
+
diff --git a/gdb/testsuite/gdb.ada/varsize_limit/pck.adb b/gdb/testsuite/gdb.ada/varsize_limit/pck.adb
new file mode 100644
index 0000000..d4acf86
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/varsize_limit/pck.adb
@@ -0,0 +1,25 @@
+--  Copyright 2018 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package body Pck is
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+   function Ident (S : String) return String is
+   begin
+      return S;
+   end Ident;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/varsize_limit/pck.ads b/gdb/testsuite/gdb.ada/varsize_limit/pck.ads
new file mode 100644
index 0000000..b0043fa
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/varsize_limit/pck.ads
@@ -0,0 +1,20 @@
+--  Copyright 2018 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+with System;
+package Pck is
+   procedure Do_Nothing (A : System.Address);
+   function Ident (S : String) return String;
+end Pck;
diff --git a/gdb/testsuite/gdb.ada/varsize_limit/vsizelim.adb b/gdb/testsuite/gdb.ada/varsize_limit/vsizelim.adb
new file mode 100644
index 0000000..e65ebfd
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/varsize_limit/vsizelim.adb
@@ -0,0 +1,23 @@
+--  Copyright 2018 Free Software Foundation, Inc.
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 3 of the License, or
+--  (at your option) any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+with Pck; use Pck;
+procedure VsizeLim is
+   Small : String := Ident ("1234567890");
+   Larger : String := Ident ("1234567890|1234567890|1234567890");
+begin
+   Do_Nothing (Small'Address); -- STOP
+   Do_Nothing (Larger'Address);
+end VsizeLim;


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