340 lines
15 KiB
Ada
340 lines
15 KiB
Ada
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------------------------------------------------------------------------------
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-- --
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-- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
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-- --
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-- S Y S T E M - S T A C K _ U S A G E --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 2004-2011, Free Software Foundation, Inc. --
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-- --
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-- GNARL is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNARL was developed by the GNARL team at Florida State University. --
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-- Extensive contributions were provided by Ada Core Technologies, Inc. --
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-- --
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------------------------------------------------------------------------------
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with System;
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with System.Storage_Elements;
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with System.Address_To_Access_Conversions;
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with Interfaces;
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package System.Stack_Usage is
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pragma Preelaborate;
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package SSE renames System.Storage_Elements;
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subtype Stack_Address is SSE.Integer_Address;
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-- Address on the stack
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function To_Stack_Address
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(Value : System.Address) return Stack_Address
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renames System.Storage_Elements.To_Integer;
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Task_Name_Length : constant := 32;
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-- The maximum length of task name displayed.
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-- ??? Consider merging this variable with Max_Task_Image_Length.
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type Task_Result is record
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Task_Name : String (1 .. Task_Name_Length);
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Value : Natural;
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-- Amount of stack used. The value is calculated on the basis of the
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-- mechanism used by GNAT to allocate it, and it is NOT a precise value.
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Stack_Size : Natural;
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-- Size of the stack
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end record;
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type Result_Array_Type is array (Positive range <>) of Task_Result;
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type Stack_Analyzer is private;
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-- Type of the stack analyzer tool. It is used to fill a portion of the
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-- stack with Pattern, and to compute the stack used after some execution.
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-- Usage:
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-- A typical use of the package is something like:
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-- A : Stack_Analyzer;
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-- task T is
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-- pragma Storage_Size (A_Storage_Size);
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-- end T;
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-- [...]
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-- Bottom_Of_Stack : aliased Integer;
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-- -- Bottom_Of_Stack'Address will be used as an approximation of
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-- -- the bottom of stack. A good practise is to avoid allocating
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-- -- other local variables on this stack, as it would degrade
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-- -- the quality of this approximation.
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-- begin
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-- Initialize_Analyzer (A,
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-- "Task t",
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-- A_Storage_Size,
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-- 0,
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-- A_Storage_Size - A_Guard,
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-- To_Stack_Address (Bottom_Of_Stack'Address));
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-- Fill_Stack (A);
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-- Some_User_Code;
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-- Compute_Result (A);
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-- Report_Result (A);
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-- end T;
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-- Errors:
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--
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-- We are instrumenting the code to measure the stack used by the user
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-- code. This method has a number of systematic errors, but several methods
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-- can be used to evaluate or reduce those errors. Here are those errors
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-- and the strategy that we use to deal with them:
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-- Bottom offset:
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-- Description: The procedure used to fill the stack with a given
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-- pattern will itself have a stack frame. The value of the stack
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-- pointer in this procedure is, therefore, different from the value
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-- before the call to the instrumentation procedure.
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-- Strategy: The user of this package should measure the bottom of stack
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-- before the call to Fill_Stack and pass it in parameter. The impact
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-- is very minor unless the stack used is very small, but in this case
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-- you aren't very interested by the figure.
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-- Instrumentation threshold at writing:
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-- Description: The procedure used to fill the stack with a given
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-- pattern will itself have a stack frame. Therefore, it will
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-- fill the stack after this stack frame. This part of the stack will
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-- appear as used in the final measure.
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-- Strategy: As the user passes the value of the bottom of stack to
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-- the instrumentation to deal with the bottom offset error, and as
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-- the instrumentation procedure knows where the pattern filling start
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-- on the stack, the difference between the two values is the minimum
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-- stack usage that the method can measure. If, when the results are
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-- computed, the pattern zone has been left untouched, we conclude
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-- that the stack usage is inferior to this minimum stack usage.
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-- Instrumentation threshold at reading:
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-- Description: The procedure used to read the stack at the end of the
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-- execution clobbers the stack by allocating its stack frame. If this
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-- stack frame is bigger than the total stack used by the user code at
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-- this point, it will increase the measured stack size.
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-- Strategy: We could augment this stack frame and see if it changes the
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-- measure. However, this error should be negligible.
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-- Pattern zone overflow:
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-- Description: The stack grows outer than the topmost bound of the
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-- pattern zone. In that case, the topmost region modified in the
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-- pattern is not the maximum value of the stack pointer during the
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-- execution.
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-- Strategy: At the end of the execution, the difference between the
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-- topmost memory region modified in the pattern zone and the
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-- topmost bound of the pattern zone can be understood as the
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-- biggest allocation that the method could have detect, provided
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-- that there is no "Untouched allocated zone" error and no "Pattern
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-- usage in user code" error. If no object in the user code is likely
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-- to have this size, this is not likely to happen.
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-- Pattern usage in user code:
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-- Description: The pattern can be found in the object of the user code.
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-- Therefore, the address space where this object has been allocated
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-- will appear as untouched.
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-- Strategy: Choose a pattern that is uncommon. 16#0000_0000# is the
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-- worst choice; 16#DEAD_BEEF# can be a good one. A good choice is an
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-- address which is not a multiple of 2, and which is not in the
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-- target address space. You can also change the pattern to see if it
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-- changes the measure. Note that this error *very* rarely influence
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-- the measure of the total stack usage: to have some influence, the
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-- pattern has to be used in the object that has been allocated on the
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-- topmost address of the used stack.
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-- Stack overflow:
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-- Description: The pattern zone does not fit on the stack. This may
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-- lead to an erroneous execution.
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-- Strategy: Specify a storage size that is bigger than the size of the
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-- pattern. 2 times bigger should be enough.
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-- Augmentation of the user stack frames:
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-- Description: The use of instrumentation object or procedure may
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-- augment the stack frame of the caller.
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-- Strategy: Do *not* inline the instrumentation procedures. Do *not*
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-- allocate the Stack_Analyzer object on the stack.
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-- Untouched allocated zone:
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-- Description: The user code may allocate objects that it will never
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-- touch. In that case, the pattern will not be changed.
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-- Strategy: There are no way to detect this error. Fortunately, this
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-- error is really rare, and it is most probably a bug in the user
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-- code, e.g. some uninitialized variable. It is (most of the time)
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-- harmless: it influences the measure only if the untouched allocated
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-- zone happens to be located at the topmost value of the stack
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-- pointer for the whole execution.
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procedure Initialize (Buffer_Size : Natural);
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pragma Export (C, Initialize, "__gnat_stack_usage_initialize");
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-- Initializes the size of the buffer that stores the results. Only the
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-- first Buffer_Size results are stored. Any results that do not fit in
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-- this buffer will be displayed on the fly.
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procedure Fill_Stack (Analyzer : in out Stack_Analyzer);
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-- Fill an area of the stack with the pattern Analyzer.Pattern. The size
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-- of this area is Analyzer.Size. After the call to this procedure,
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-- the memory will look like that:
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--
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-- Stack growing
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-- ---------------------------------------------------------------------->
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-- |<--------------------->|<----------------------------------->|
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-- | Stack frames to | Memory filled with Analyzer.Pattern |
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-- | Fill_Stack | |
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-- ^ | ^
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-- Analyzer.Stack_Base | Analyzer.Pattern_Limit
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-- ^
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-- Analyzer.Pattern_Limit +/- Analyzer.Pattern_Size
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--
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procedure Initialize_Analyzer
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(Analyzer : in out Stack_Analyzer;
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Task_Name : String;
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Stack_Size : Natural;
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Stack_Base : Stack_Address;
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Pattern_Size : Natural;
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Pattern : Interfaces.Unsigned_32 := 16#DEAD_BEEF#);
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-- Should be called before any use of a Stack_Analyzer, to initialize it.
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-- Max_Pattern_Size is the size of the pattern zone, might be smaller than
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-- the full stack size Stack_Size in order to take into account e.g. the
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-- secondary stack and a guard against overflow. The actual size taken
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-- will be readjusted with data already used at the time the stack is
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-- actually filled.
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Is_Enabled : Boolean := False;
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-- When this flag is true, then stack analysis is enabled
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procedure Compute_Result (Analyzer : in out Stack_Analyzer);
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-- Read the pattern zone and deduce the stack usage. It should be called
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-- from the same frame as Fill_Stack. If Analyzer.Probe is not null, an
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-- array of Unsigned_32 with Analyzer.Probe elements is allocated on
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-- Compute_Result's stack frame. Probe can be used to detect the error:
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-- "instrumentation threshold at reading". See above. After the call
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-- to this procedure, the memory will look like:
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--
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-- Stack growing
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-- ----------------------------------------------------------------------->
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-- |<---------------------->|<-------------->|<--------->|<--------->|
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-- | Stack frames | Array of | used | Memory |
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-- | to Compute_Result | Analyzer.Probe | during | filled |
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-- | | elements | the | with |
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-- | | | execution | pattern |
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-- | | |
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-- |<----------------------------------------------------> |
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-- Stack used ^
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-- Pattern_Limit
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procedure Report_Result (Analyzer : Stack_Analyzer);
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-- Store the results of the computation in memory, at the address
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-- corresponding to the symbol __gnat_stack_usage_results. This is not
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-- done inside Compute_Result in order to use as less stack as possible
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-- within a task.
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procedure Output_Results;
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-- Print the results computed so far on the standard output. Should be
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-- called when all tasks are dead.
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pragma Export (C, Output_Results, "__gnat_stack_usage_output_results");
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private
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package Unsigned_32_Addr is
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new System.Address_To_Access_Conversions (Interfaces.Unsigned_32);
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subtype Pattern_Type is Interfaces.Unsigned_32;
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Bytes_Per_Pattern : constant := Pattern_Type'Object_Size / Storage_Unit;
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type Stack_Analyzer is record
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Task_Name : String (1 .. Task_Name_Length);
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-- Name of the task
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Stack_Base : Stack_Address;
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-- Address of the base of the stack, as given by the caller of
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-- Initialize_Analyzer.
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Stack_Size : Natural;
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-- Entire size of the analyzed stack
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Pattern_Size : Natural;
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-- Size of the pattern zone
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Pattern : Pattern_Type;
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-- Pattern used to recognize untouched memory
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Pattern_Limit : Stack_Address;
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-- Bound of the pattern area farthest to the base
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Topmost_Touched_Mark : Stack_Address;
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-- Topmost address of the pattern area whose value it is pointing
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-- at has been modified during execution. If the systematic error are
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-- compensated, it is the topmost value of the stack pointer during
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-- the execution.
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Pattern_Overlay_Address : System.Address;
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-- Address of the stack abstraction object we overlay over a
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-- task's real stack, typically a pattern-initialized array.
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Result_Id : Positive;
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-- Id of the result. If less than value given to gnatbind -u corresponds
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-- to the location in the result array of result for the current task.
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end record;
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Environment_Task_Analyzer : Stack_Analyzer;
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Compute_Environment_Task : Boolean;
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type Result_Array_Ptr is access all Result_Array_Type;
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Result_Array : Result_Array_Ptr;
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pragma Export (C, Result_Array, "__gnat_stack_usage_results");
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-- Exported in order to have an easy accessible symbol in when debugging
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Next_Id : Positive := 1;
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-- Id of the next stack analyzer
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function Stack_Size
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(SP_Low : Stack_Address;
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SP_High : Stack_Address) return Natural;
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pragma Inline (Stack_Size);
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-- Return the size of a portion of stack delimited by SP_High and SP_Low
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-- (), i.e. the difference between SP_High and SP_Low. The storage element
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-- pointed by SP_Low is not included in the size. Inlined to reduce the
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-- size of the stack used by the instrumentation code.
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end System.Stack_Usage;
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