Where do your variables stored - Revision history

Proj user12 at 02:46, 24 April 2017

2017-04-24T02:46:53Z

Proj user12: /* BSS and Data Segments */

2017-04-24T02:43:01Z

‎BSS and Data Segments

Proj user12: /* BSS and Data Segments */

2017-04-24T02:41:33Z

‎BSS and Data Segments

Proj user16: /* BSS and Data Segments */

2016-12-19T02:28:57Z

‎BSS and Data Segments

Proj user16: /* BSS and Data Segments */

2016-12-19T02:09:00Z

‎BSS and Data Segments

Proj user16: /* BSS and Data Segments */

2016-12-17T09:42:35Z

‎BSS and Data Segments

Proj user16: /* BSS and Data Segments */

2016-12-17T09:30:00Z

‎BSS and Data Segments

Proj user16: /* BSS and Data Segments */

2016-12-17T09:24:19Z

‎BSS and Data Segments

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Proj user16: Created page with "=== BSS and Data Segments ===

 What are text,.bss and data sections in an Embedded C program?  Where do your program recide?Obviously memory,but how is it organized? In..."

2016-12-10T21:11:35Z

Created page with "=== BSS and Data Segments === <pre> What are text,.bss and data sections in an Embedded C program? Where do your program recide?Obviously memory,but how is it organized? In..."

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=== BSS and Data Segments ===

<pre>
What are text,.bss and data sections in an Embedded C program?

Where do your program recide?Obviously memory,but how is it organized?
In embedded systems ,which are RAM-memory constrained ,memory map is divided into segments
called text,data and bss.

Text segment:Contains code and constants of the program.Text section is allocated on flash.
Eg1: a.out :executable code
Eg2:const uint8_t i=8 :contant
Eg3:

#include <stdio.h>
const int global_var=20;
int data_variable = 500;
static int static_var=10;
void foo(){
const int local_constant=100;
int local;
local = 3;
int un_initialized;
int another_initialized=0;
static int local_static=9;
local_static++;
printf("local varaible is %d\n", local);
}

In the above example, executable code of the program is stored in flash and const variable global_var=20 and local_constant=100 are stored in flash.

Data segment:Initialized variables are stored in this section.
Initially values are stored in flash and copied into RAM during execution
through copy down process.

Eg: uint8_t j=10; initialized variable

In the code given above int data_variable = 500,static int static_var=10,local = 3, and local_static=9 are stored in data segment of flash.

.bss segment:Uninitialized variables are stored in bss section.

In embedded software, the bss segment is mapped into memory that is initialized to zero by the C run-time system before main() is entered.
(wiki :https://en.wikipedia.org/wiki/.bss#BSS_in_C)

Eg:int newvar;

In the above code un_initialized(after initializing it to zero) and another_initialized are stored in bss section ;

Simple example:

#include <stdio.h>
int main(void)
{
return 0;
}
Memory occupied by the above program:

$ gcc -o just_main just_main.c
$ size just_main.exe
text data bss dec hex filename
3153 1976 448 5577 15c9 just_main.exe
After modifying the above program with one global variable:

#include <stdio.h>
int global_var;
int main(void)
{
return 0;
}

$ gcc -o just_main just_main.c
$ size just_main.exe
text data bss dec hex filename
3153 1976 464 5593 15d9 just_main.exe
bss section is increased by 2 bytes;

Modify the above program with global variable initialized to zero;

#include <stdio.h>
int global_var=0;
int main(void)
{
return 0;
}

$ gcc -o just_main just_main.c
$ size just_main.exe
text data bss dec hex filename
3153 1976 480 5609 15e9 just_main.exe
bss segment is increased by 32 bits(4 bytes)

Modify the above program with global variable initialized to non-zero;

#include <stdio.h>
int global_var=8;
int main(void)
{
return 0;
}
$ gcc -o just_main just_main
$ size just_main.exe
text data bss dec hex filename
3153 1976 448 5577 15c9 just_main.exe
bss section is not modified.

FAQ:
What is the size of bss segment?
bss does not take any space in the object file and stores the count of variables that can be given initial values.Hence occupy 4 or 8 bytes
depending on the implementation.

What is the amount of RAM being used?
Memory occupied by bss and data segments added together.

</pre>

@@ Line 1: / Line 1: @@
 === BSS and Data Segments ===
 What are text,.bss and data sections in an Embedded C program?
-Where does your program reside? Obviously memory,but how is it organized?
+Where does your program reside? Obviously memory, but how is it organized?
-In embedded systems ,which are RAM-memory constrained ,memory map is divided into segments
+In embedded systems, which are RAM-memory constrained, memory map is divided into segments
-called text,data and bss.
+called text, data and bss.
 '''Text segment:'''
@@ Line 55: / Line 56: @@
 Initialized variables are stored in this section.
-Initially values are stored in flash and copied into RAM during execution
+Initially, values are stored in flash and copied into RAM during execution
 through copy down process.

@@ Line 59: / Line 59: @@
 Eg: uint8_t j=10; --------initialized variable
-In the code given above int data_variable = 500,static int static_var=10,local = 3, and local_static=9 are stored in data segment of flash.
+In the code given above int data_variable = 500,static int static_var=10,local = 3, and local_static=9 are stored in data segment.
 '''.bss segment:'''

@@ Line 15: / Line 15: @@
 	Eg1: a.out :executable code
-	Eg2:const uint8_t i=8 :contant
+	Eg2: const uint8_t i=8 :contant
 	Eg3:

@@ Line 17: / Line 17: @@
 	Eg3:
-	<pre>
+<syntaxhighlight lang="C">
 	#include <stdio.h>
@@ Line 29: / Line 29: @@
 	void foo()
+         {
-	   const int local_constant=100;
+          const int local_constant=100;
-           int local;
+          int local;
-           local = 3;
+          local = 3;
-           int un-initialized;
+          int un-initialized;
-	   int another-initialized=0;
+          local_static++;
 In the above example, executable code of the program is stored in flash and const variable global_var=20
@@ Line 75: / Line 76: @@
 	'''Simple example:'''
-        <pre>
+<syntaxhighlight lang="C">
-	#include <stdio.h>
+    #include <stdio.h>
 	int main(void)
@@ Line 83: / Line 84: @@
 		return 0;
+	}
-        </pre>
 Memory occupied by the above program:
-−
-        <pre>
+<syntaxhighlight lang="C">
 	$ gcc -o just_main just_main.c
@@ Line 95: / Line 99: @@
     1976     448    5577    15c9 just_main.exe
-        </pre>
+</syntaxhighlight>
 After modifying the above program with one global variable:
-        <pre>
+<syntaxhighlight lang="C">
-	#include <stdio.h>
+     #include <stdio.h>
 	int global_var;
@@ Line 110: / Line 114: @@
+	}
-        </pre>
+</syntaxhighlight>
 Memory map of the above program looks like:
-        <pre>
+      $ gcc -o just_main just_main.c
 	$ size just_main.exe
@@ Line 123: / Line 128: @@
     1976     464    5593    15d9 just_main.exe
-         </pre>
 bss section is increased by 2 bytes;
@@ Line 129: / Line 135: @@
 Modify the above program with global variable initialized to zero;
-        <pre>
+<syntaxhighlight lang="C">
-	#include <stdio.h>
+     #include <stdio.h>
 	int global_var=0;
@@ Line 140: / Line 146: @@
+	}
-        </pre>
+</syntaxhighlight>
 Data and bss segments occupy the RAM area as below.
-         <pre>
+         <syntaxhighlight lang="C">
 	$ gcc -o just_main just_main.c
@@ Line 153: / Line 159: @@
     1976     480    5609    15e9 just_main.exe
-         </pre>
+         </syntaxhighlight>
 bss segment is increased by 32 bits(4 bytes)
@@ Line 159: / Line 165: @@
 Modify the above program with global variable initialized to non-zero;
-        <pre>
+<syntaxhighlight lang="C">
-	#include <stdio.h>
+      #include <stdio.h>
 	int global_var=8;
@@ Line 170: / Line 176: @@
+	}
-        </pre>
+</syntaxhighlight>
 RAM memory is occupied by bss and data as below
-        <pre>
+<syntaxhighlight lang="C">
 	$ gcc -o just_main just_main
@@ Line 183: / Line 189: @@
     1976     448    5577    15c9 just_main.exe
-        </pre>
 bss section is not modified.