Glibc, SVN and Qt

SUSE:

QT4: http://www.linuxfromscratch.org/blfs/view/svn/x/qt4.html

Installation Guidelines: http://doc.trolltech.com/4.4/install-x11.html

SVN:

• libapr-1: http://www.rpmfind.net/linux/rpm2html/search.php?query=libapr-1.so.0
• libaprutil: http://software.opensuse.org/search?baseproject=ALL&p=1&q=subversion
• SVN: http://software.opensuse.org/search?baseproject=ALL&p=1&q=subversion

REDHAT and FEDORA

GLIBC-3.4.9 (64-bit): http://rpm.pbone.net/index.php3/stat/4/idpl/12189689/com/libstdc++-4.4.0-0.20.x86_64.rpm.html

GLIBC-3.4.9(32 bit): http://rpm.pbone.net/index.php3?stat=26&dist=32&size=321482&name=libstdc%2B%2B-4.4.0-0.20.i586.rpm

unresolved external symbol

unresolved external symbol __imp___CrtDbgReportW:

1. When u get this error, go to visual studio project settings -> C/C++ ->
Code Generation -> RunTime Library has the "debug" enabled (ex: Multi Threaded Debug DLL).
If not enabled, enable it and rebuild again.

2. Also check if Linker->Debugging->Generate Debug Info is on or not

Good Quotes

1. “It’s supposed to be hard; if it wasn’t hard everyone would do it. The hard is what makes it great.” -- Tom Hanks
2. "Being in the right place at the right time won’t make you a success – unless you’re ready. The important question is: Are you ready?” -- Johnny Carson
3. If at first you dont' succeed, cal it version 1.0
4. If you are willing to admit faults, you have one less fault to admit

Mentioning Library path for .lib (s)

If you have dependency on some .libs, you cannot specify this path of .libs in "Include" path of your project. In order to specify the path, you need to specify the path of .libs in "Linker" as shown, in "Additional Library Directories" of General Category.

Changing the user name while inserting comment

1. Go to Review Tab.

2. Select the "Track Changes" combo

3. Select "Change User Name"

4. In the "Popular" page, at the bottom you wud find "Initials". Enter your initials there.

Data Execution Prevention (DEP)

DEP is a security feature included in modern Microsoft Windows OS that is intended to prevent an application or service from executing code from a non-executable memory region.

It is a system-level memory protection feature that is built into OS starting with Windows XP and Windows Server 2003.

DEP enables the system to mark one or more pages of memory as non-executable. Marking memory regions as non-executable means that code cannot be run from that region of memory, which makes it harder for the exploitation of buffer overruns (buffer overflow). It is a set of hardware and software technologies that perform additional checks on memory to help protect against malicious code exploits.

• This level of pagin has been introduced with AMD64 (the ability to indicate that code should not be executed from a page or a set of pages by setting NX bit = 1; this is 63rd bit in 64-bit entry in the page table)
• This feature is enabled if NO execute bit in Enable Feature Extended Register (EFER.NXE) and the PAE in CR4 are set, regardless of operating mode (this is because x86's original 32-bit page table format obviously has no bit 63)

Modes of Enforcement

1. Hardware Enforcement: Achieving this DEP using NX bit (bit number 63) of a 64-bit Page Translation Entry. It marks all memory locations in a process as non-executable unless the location explicitly contains executable code. There is a class of attacks that attempt to insert and execute code from non-executable memory locations. DEP helps prevent these attacks by intercepting them and raising an exception.
2. Software Enforcement: System software (kernel) can mark pages used for program stacks and data sections as non-executable.

Processor-corresponding features

1. AMD: Enhanced Virus Protection (EVP in AMD64)
2. Intel: Execute Disable (XD in EM64T)

Page State

Any page in VAS (PAS) of a process can be in one of the three states.

1. Committed: A page state of a page which is mapped to a page frame in physical memory (or to a page-sized entry in a file on disk)
2. Reserved: A page state of a page which been set aside for future use so that it cannot be re-used for any other purpose within the process, but has no associated physical page storage
3. Free: A page state of a page which is available to be reserved

Copy-On-Write

Copy-On-Write (COW)

1. optimization strategy used in computer systems
2. Idea is that if multiple callers ask for resources, they can all be given pointers to the same resource. Now, all "callers" (processes) will be in assumption that "I m holding this X resource; and I can do whatever I want". But, when this "caller" tries to modify its so - called "My resource X", a true private copy is created actually, to prevent the changes becoming visible to other "callers".
3. Hence, the primary advandage is that if a caller never makes any modifications, *NO PRIVATE COPY IS CREATED*.

In Virtual Memory:

• COW finds its main-use in virtual memory OS; when a process creates a copy of itself (fork), the pages in memory that might be modified by either the process or its copy, are marked "Copy-On-Write".
• When one process modifies the memory, the OS kernel intercepts the operation and copies the memory so that changes in one process's memory are not visible to other

COW and MMU

• COW can be implemented by telling MMU that certain pages in the process's address space are read only.
• When data is written to these pages, MMU raises an exception which is handled by kernel, which allocates new space in physical memory and makes the page being written to correspond to that new location in physical memory

Basics of Memory Management

Memory Manager:

Implements virtual memory, provides a core set of services such as memory mapped files, copy-on-write memory, large memory support and underlying support for the cache manager.

(For details on Copy-on-Write http://spot-myblog.blogspot.com/2009/07/copy-on-write.html)

Each process on a 32-bit Windows OS has a virtual address space (PAS) of 4GB (It is 8TB for a process in 64-bit Windows). Threads cannot access memory that belongs to another process, which protects a process from being corrupted by another process.

VAS (PAS):

• VAS for a process is the set of virtual memory addresses that it can use. The address space of a process P1, cannot be accessed by other process(es) P2, *unless it is shared*.
• This PAS does not represent the actual physical location in memory; instead the system maintains a Page Table for each process (an internal data structure used to translate VA to PA). Each time a thread references an address, the system translates the VA to PA.
• VAS for 32-bit (Windows) process is divided into two partitions; one for process itself and the other for kernel. Default partition will be 2GB:2GB (0x00000000 - 0x7FFFFFFF: 0x80000000 - 0xFFFFFFFF). If 4GT (4GB Tuning) is enabled, then it will be 3GB:1GB (0x00000000 - 0xBFFFFFFF: 0xC0000000 - 0xFFFFFFFF).
• After 4GT, the process that has IMAGE_FILE_LARGE_ADDRESS_AWARE flag set in its image header will have access to the additional 1GB of memory above the low 2GB.

IMPORTANT NOTE:

We can adjust the VAS of 32-bit process, using the following command, which sets a boot entry option that configures the size of the partition that is available for use by the process to a value between 2048 MB (2GB) and 3072 MB(3GB).

BCDEdit /set increaseuserva <XYZ Megabytes>

after which, partition would be like (0x00000000 - XYZ: XYZ+1 - 0xFFFFFFFF).

Working Set:

• The subset of VAS of a process that resides in physical memory is known as "Working Set"
• If the thread of a process attemt to use more physical memory than is currently available, the kernel, "pages" (swaps) some of the memory contents to disk (the total amount of VAS available to a process is limited by physical memory and the free space on disk available for the paging file)
• Physical storage and the VAS of each process are organized into "pages", units of memory, whose size depends on the host computer (usually 4 KB for x86 computers - Use GetSystemInfo API to get the page size)
• When a thread needs space in RAM, the kernel moves the "least recently used" pages in RAM to paging file in disk.
• When a thread references a page that is not a part of Working Set (means not present in main memory, a "page fault"(called Page Exception) occurs, on which Kernel's Page Fault Handler attempts to resolve the page fault (by "Demand Paging") and if it succeeds, the page is added to the working set.
• Hard Page Fault: Occurs when the demanded page is not on Main Memory
• Soft Page Fault: Occurs when the demanded page is on Main memory but in the working set of some other process or if it is demanded for the first time (called "Demand-Zero" fault)
• Process can reduce or empty its working set by calling "SetProcessWorkingSetSize" or "EmptyWorkingSet" functions

PS: The details on the page state at http://spot-myblog.blogspot.com/2009/07/page-state.html

DLL - Programming basics

Points to be noted:

1. __declspec() : Declares the following class or function to be exported/imported (mainly). For example, __declspec(dllexport) void func() {} implies, func() is exported for applications use
2. Wondering, when my app could not able to get the handle of exported APIs when the .h file of DLL had the definitions. When i moved the definitions to .cpp file of DLL project, my app could get the handle successfully
3. If using visual studio, you can use "Pre-Build Event" (under Build Events) to copy the DLL to the app folder
4. When using LoadLibrary call, due to UNICODE probs, the dll may not get loaded. Hence use _T casting like hHandle = LoadLibrary( _T ( "mydll.dll" ) );
5. To check the "sections" contained in the DLL, open the Visual Studio command prompt (not the normal windows prompt) and go to the directory which has the dll file, and type dumpbin /exports mydll.dll

===============================

DLL CODE

===============================

/*

* This is .h file of a DLL

*/

#include <windows.h>

/* If we try to export all the APIs to the app by preceding each API with __declspec(dllexport)

* then the corresponding API will always be exported even when app does not require it.

* For this very reason, DLL developer tries to export it from his project, where as the

* app developer, will try to import it in his code. */

#if defined EXPORT_DIR

#define DECLAPI __declspec( dllexport )

#else

#define DECLAPI __declspec( dllimport )

#endif

/* Tell the compiler that its OK to use these APIs in either C or C++ */

extern "C"

{

DECLAPI int addition( int a, int b );

DECLAPI int multiply( int a, int b );

}

/*

* This is .cpp file of DLL project

*/

#include "mydll.h"

/* [Important]: Define this macro to try to export the APIs (even though not catched by apps) */

#define EXPORT_DIR

extern "C"

{

DECLAPI int addition ( int a, int b ) { return a + b; }

DECLAPI int multiply ( int a, int b ) { return a * b; }

}

================================

APP Code

================================

/*

* This is the application which uses the DLLs

*/

#include <iostream>

#include <windows.h>

typedef int ( *Addition ) ( int, int );

typedef int ( *Multiply ) ( int, int );

int main()

{

HINSTANCE hInstance;

Addition additionPtr;

Multiply multiplyPtr;

hInstance = LoadLibrary( _T ( "mydll.dll" ) );

if( hInstance )

{

additionPtr = ( Addition ) GetProcAddress ( hInstance, "addition" );

multiplyPtr = ( Multiply ) GetProcAddress ( hInstance, "multiply" );

if( additionPtr )

printf( "DLL addition called and sum: %d.\n", additionPtr( 10, 5 ) );

if( multiplyPtr )

printf( "DLL multiply called and sum: %d.\n", multiplyPtr( 10, 5 ) );

FreeLibrary( hInstance );

}

else

{

printf( "Failed to load mydll.dll!!!!..\n" );

}

return 0;

}