------------------------------------------------------------------------------ -- -- -- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS -- -- -- -- S Y S T E M - S T A C K _ U S A G E -- -- -- -- S p e c -- -- -- -- Copyright (C) 2004-2005, Free Software Foundation, Inc. -- -- -- -- GNARL is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 2, or (at your option) any later ver- -- -- sion. GNARL is distributed in the hope that it will be useful, but WITH- -- -- OUT 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 distributed with GNARL; see file COPYING. If not, write -- -- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, -- -- Boston, MA 02110-1301, USA. -- -- -- -- As a special exception, if other files instantiate generics from this -- -- unit, or you link this unit with other files to produce an executable, -- -- this unit does not by itself cause the resulting executable to be -- -- covered by the GNU General Public License. This exception does not -- -- however invalidate any other reasons why the executable file might be -- -- covered by the GNU Public License. -- -- -- -- GNARL was developed by the GNARL team at Florida State University. -- -- Extensive contributions were provided by Ada Core Technologies, Inc. -- -- -- ------------------------------------------------------------------------------ with System; with System.Storage_Elements; with System.Address_To_Access_Conversions; package System.Stack_Usage is pragma Preelaborate; package SSE renames System.Storage_Elements; Byte_Size : constant := 8; Word_32_Size : constant := 4 * Byte_Size; type Word_32 is mod 2 ** Word_32_Size; for Word_32'Alignment use 4; subtype Stack_Address is SSE.Integer_Address; -- Address on the stack -- -- Note: in this package, when comparing two addresses on the stack, the -- comments use the terms "outer", "inner", "outermost" and "innermost" -- instead of the ambigous "higher", "lower", "highest" and "lowest". -- "inner" means "closer to the bottom of stack" and is the contrary of -- "outer". "innermost" means "closest address to the bottom of stack". The -- stack is growing from the inner to the outer. -- Top/Bottom would be much better than inner and outer ??? function To_Stack_Address (Value : System.Address) return Stack_Address renames System.Storage_Elements.To_Integer; type Stack_Analyzer is private; -- Type of the stack analyzer tool. It is used to fill a portion of -- the stack with Pattern, and to compute the stack used after some -- execution. -- Usage: -- A typical use of the package is something like: -- A : Stack_Analyzer; -- task T is -- pragma Storage_Size (A_Storage_Size); -- end T; -- [...] -- Bottom_Of_Stack : aliased Integer; -- -- Bottom_Of_Stack'Address will be used as an approximation of -- -- the bottom of stack. A good practise is to avoid allocating -- -- other local variables on this stack, as it would degrade -- -- the quality of this approximation. -- begin -- Initialize_Analyzer (A, -- "Task t", -- A_Storage_Size - A_Guard, -- To_Stack_Address (Bottom_Of_Stack'Address)); -- Fill_Stack (A); -- Some_User_Code; -- Compute_Result (A); -- Report_Result (A); -- end T; -- Errors: -- -- We are instrumenting the code to measure the stack used by the user -- code. This method has a number of systematic errors, but several -- methods can be used to evaluate or reduce those errors. Here are -- those errors and the strategy that we use to deal with them: -- Bottom offset: -- Description: The procedure used to fill the stack with a given -- pattern will itself have a stack frame. The value of the stack -- pointer in this procedure is, therefore, different from the value -- before the call to the instrumentation procedure. -- Strategy: The user of this package should measure the bottom of stack -- before the call to Fill_Stack and pass it in parameter. -- Instrumentation threshold at writing: -- Description: The procedure used to fill the stack with a given -- pattern will itself have a stack frame. Therefore, it will -- fill the stack after this stack frame. This part of the stack will -- appear as used in the final measure. -- Strategy: As the user passes the value of the bottom of stack to -- the instrumentation to deal with the bottom offset error, and as as -- the instrumentation procedure knows where the pattern filling start -- on the stack, the difference between the two values is the minimum -- stack usage that the method can measure. If, when the results are -- computed, the pattern zone has been left untouched, we conclude -- that the stack usage is inferior to this minimum stack usage. -- Instrumentation threshold at reading: -- Description: The procedure used to read the stack at the end of the -- execution clobbers the stack by allocating its stack frame. If this -- stack frame is bigger than the total stack used by the user code at -- this point, it will increase the measured stack size. -- Strategy: We could augment this stack frame and see if it changes the -- measure. However, this error should be negligeable. -- Pattern zone overflow: -- Description: The stack grows outer than the outermost bound of the -- pattern zone. In that case, the outermost region modified in the -- pattern is not the maximum value of the stack pointer during the -- execution. -- Strategy: At the end of the execution, the difference between the -- outermost memory region modified in the pattern zone and the -- outermost bound of the pattern zone can be understood as the -- biggest allocation that the method could have detect, provided -- that there is no "Untouched allocated zone" error and no "Pattern -- usage in user code" error. If no object in the user code is likely -- to have this size, this is not likely to happen. -- Pattern usage in user code: -- Description: The pattern can be found in the object of the user code. -- Therefore, the address space where this object has been allocated -- will appear as untouched. -- Strategy: Choose a pattern that is uncommon. 16#0000_0000# is the -- worst choice; 16#DEAD_BEEF# can be a good one. A good choice is an -- address which is not a multiple of 2, and which is not in the -- target address space. You can also change the pattern to see if it -- changes the measure. Note that this error *very* rarely influence -- the measure of the total stack usage: to have some influence, the -- pattern has to be used in the object that has been allocated on the -- outermost address of the used stack. -- Stack overflow: -- Description: The pattern zone does not fit on the stack. This may -- lead to an erroneous execution. -- Strategy: Specify a storage size that is bigger than the size of the -- pattern. 2 times bigger should be enough. -- Augmentation of the user stack frames: -- Description: The use of instrumentation object or procedure may -- augment the stack frame of the caller. -- Strategy: Do *not* inline the instrumentation procedures. Do *not* -- allocate the Stack_Analyzer object on the stack. -- Untouched allocated zone: -- Description: The user code may allocate objects that it will never -- touch. In that case, the pattern will not be changed. -- Strategy: There are no way to detect this error. Fortunately, this -- error is really rare, and it is most probably a bug in the user -- code, e.g. some uninitialized variable. It is (most of the time) -- harmless: it influences the measure only if the untouched allocated -- zone happens to be located at the outermost value of the stack -- pointer for the whole execution. procedure Initialize (Buffer_Size : Natural); pragma Export (C, Initialize, "__gnat_stack_usage_initialize"); -- Initializes the size of the buffer that stores the results. Only the -- first Buffer_Size results are stored. Any results that do not fit in -- this buffer will be displayed on the fly. procedure Fill_Stack (Analyzer : in out Stack_Analyzer); -- Fill an area of the stack with the pattern Analyzer.Pattern. The size -- of this area is Analyzer.Size. After the call to this procedure, -- the memory will look like that: -- -- Stack growing -- -----------------------------------------------------------------------> -- |<---------------------->|<----------------------------------->| -- | Stack frame | Memory filled with Analyzer.Pattern | -- | of Fill_Stack | | -- | (deallocated at | | -- | the end of the call) | | -- ^ | | -- Analyzer.Bottom_Of_Stack ^ | -- Analyzer.Inner_Pattern_Mark ^ -- Analyzer.Outer_Pattern_Mark procedure Initialize_Analyzer (Analyzer : in out Stack_Analyzer; Task_Name : String; Size : Natural; Bottom : Stack_Address; Pattern : Word_32 := 16#DEAD_BEEF#); -- Should be called before any use of a Stack_Analyzer, to initialize it. -- Size is the size of the pattern zone. Bottom should be a close -- approximation of the caller base frame address. Is_Enabled : Boolean := False; -- When this flag is true, then stack analysis is enabled procedure Compute_Result (Analyzer : in out Stack_Analyzer); -- Read the patern zone and deduce the stack usage. It should be called -- from the same frame as Fill_Stack. If Analyzer.Probe is not null, an -- array of Word_32 with Analyzer.Probe elements is allocated on -- Compute_Result's stack frame. Probe can be used to detect the error: -- "instrumentation threshold at reading". See above. After the call -- to this procedure, the memory will look like: -- -- Stack growing -- -----------------------------------------------------------------------> -- |<---------------------->|<-------------->|<--------->|<--------->| -- | Stack frame | Array of | used | Memory | -- | of Compute_Result | Analyzer.Probe | during | filled | -- | (deallocated at | elements | the | with | -- | the end of the call) | | execution | pattern | -- | ^ | | | -- | Inner_Pattern_Mark | | | -- | | | -- |<----------------------------------------------------> | -- Stack used ^ -- Outer_Pattern_Mark procedure Report_Result (Analyzer : Stack_Analyzer); -- Store the results of the computation in memory, at the address -- corresponding to the symbol __gnat_stack_usage_results. This is not -- done inside Compute_Resuls in order to use as less stack as possible -- within a task. procedure Output_Results; -- Print the results computed so far on the standard output. Should be -- called when all tasks are dead. pragma Export (C, Output_Results, "__gnat_stack_usage_output_results"); private Task_Name_Length : constant := 32; package Word_32_Addr is new System.Address_To_Access_Conversions (Word_32); type Stack_Analyzer is record Task_Name : String (1 .. Task_Name_Length); -- Name of the task Size : Natural; -- Size of the pattern zone Pattern : Word_32; -- Pattern used to recognize untouched memory Inner_Pattern_Mark : Stack_Address; -- Innermost bound of the pattern area on the stack Outer_Pattern_Mark : Stack_Address; -- Outermost bound of the pattern area on the stack Outermost_Touched_Mark : Stack_Address; -- Outermost address of the pattern area whose value it is pointing -- at has been modified during execution. If the systematic error are -- compensated, it is the outermost value of the stack pointer during -- the execution. Bottom_Of_Stack : Stack_Address; -- Address of the bottom of the stack, as given by the caller of -- Initialize_Analyzer. Array_Address : System.Address; -- Address of the array of Word_32 that represents the pattern zone First_Is_Outermost : Boolean; -- Set to true if the first element of the array of Word_32 that -- represents the pattern zone is at the outermost address of the -- pattern zone; false if it is the innermost address. Result_Id : Positive; -- Id of the result. If less than value given to gnatbind -u corresponds -- to the location in the result array of result for the current task. end record; Environment_Task_Analyzer : Stack_Analyzer; Compute_Environment_Task : Boolean; type Task_Result is record Task_Name : String (1 .. Task_Name_Length); Measure : Natural; Max_Size : Natural; end record; type Result_Array_Type is array (Positive range <>) of Task_Result; type Result_Array_Ptr is access all Result_Array_Type; Result_Array : Result_Array_Ptr; pragma Export (C, Result_Array, "__gnat_stack_usage_results"); -- Exported in order to have an easy accessible symbol in when debugging Next_Id : Positive := 1; -- Id of the next stack analyzer function Stack_Size (SP_Low : Stack_Address; SP_High : Stack_Address) return Natural; pragma Inline (Stack_Size); -- Return the size of a portion of stack delimeted by SP_High and SP_Low -- (), i.e. the difference between SP_High and SP_Low. The storage element -- pointed by SP_Low is not included in the size. Inlined to reduce the -- size of the stack used by the instrumentation code. end System.Stack_Usage;