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------------------------------------------------------------------------------ -- -- -- 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) 2004-2011, 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 3, or (at your option) any later ver- -- -- sion. GNAT 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. -- -- -- -- As a special exception under Section 7 of GPL version 3, you are granted -- -- additional permissions described in the GCC Runtime Library Exception, -- -- version 3.1, as published by the Free Software Foundation. -- -- -- -- You should have received a copy of the GNU General Public License and -- -- a copy of the GCC Runtime Library Exception along with this program; -- -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- -- <http://www.gnu.org/licenses/>. -- -- -- -- 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; with Interfaces; package System.Stack_Usage is pragma Preelaborate; package SSE renames System.Storage_Elements; subtype Stack_Address is SSE.Integer_Address; -- Address on the stack function To_Stack_Address (Value : System.Address) return Stack_Address renames System.Storage_Elements.To_Integer; Task_Name_Length : constant := 32; -- The maximum length of task name displayed. -- ??? Consider merging this variable with Max_Task_Image_Length. type Task_Result is record Task_Name : String (1 .. Task_Name_Length); Value : Natural; -- Amount of stack used. The value is calculated on the basis of the -- mechanism used by GNAT to allocate it, and it is NOT a precise value. Stack_Size : Natural; -- Size of the stack end record; type Result_Array_Type is array (Positive range <>) of Task_Result; 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, -- 0, -- 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. The impact -- is very minor unless the stack used is very small, but in this case -- you aren't very interested by the figure. -- 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 -- 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 negligible. -- Pattern zone overflow: -- Description: The stack grows outer than the topmost bound of the -- pattern zone. In that case, the topmost 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 -- topmost memory region modified in the pattern zone and the -- topmost 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 -- topmost 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 topmost 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 frames to | Memory filled with Analyzer.Pattern | -- | Fill_Stack | | -- ^ | ^ -- Analyzer.Stack_Base | Analyzer.Pattern_Limit -- ^ -- Analyzer.Pattern_Limit +/- Analyzer.Pattern_Size -- procedure Initialize_Analyzer (Analyzer : in out Stack_Analyzer; Task_Name : String; Stack_Size : Natural; Stack_Base : Stack_Address; Pattern_Size : Natural; Pattern : Interfaces.Unsigned_32 := 16#DEAD_BEEF#); -- Should be called before any use of a Stack_Analyzer, to initialize it. -- Max_Pattern_Size is the size of the pattern zone, might be smaller than -- the full stack size Stack_Size in order to take into account e.g. the -- secondary stack and a guard against overflow. The actual size taken -- will be readjusted with data already used at the time the stack is -- actually filled. Is_Enabled : Boolean := False; -- When this flag is true, then stack analysis is enabled procedure Compute_Result (Analyzer : in out Stack_Analyzer); -- Read the pattern 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 Unsigned_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 frames | Array of | used | Memory | -- | to Compute_Result | Analyzer.Probe | during | filled | -- | | elements | the | with | -- | | | execution | pattern | -- | | | -- |<----------------------------------------------------> | -- Stack used ^ -- Pattern_Limit 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_Result 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 package Unsigned_32_Addr is new System.Address_To_Access_Conversions (Interfaces.Unsigned_32); subtype Pattern_Type is Interfaces.Unsigned_32; Bytes_Per_Pattern : constant := Pattern_Type'Object_Size / Storage_Unit; type Stack_Analyzer is record Task_Name : String (1 .. Task_Name_Length); -- Name of the task Stack_Base : Stack_Address; -- Address of the base of the stack, as given by the caller of -- Initialize_Analyzer. Stack_Size : Natural; -- Entire size of the analyzed stack Pattern_Size : Natural; -- Size of the pattern zone Pattern : Pattern_Type; -- Pattern used to recognize untouched memory Pattern_Limit : Stack_Address; -- Bound of the pattern area farthest to the base Topmost_Touched_Mark : Stack_Address; -- Topmost 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 topmost value of the stack pointer during -- the execution. Pattern_Overlay_Address : System.Address; -- Address of the stack abstraction object we overlay over a -- task's real stack, typically a pattern-initialized array. 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 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 delimited 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;
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