Log whether a global variable has been read or written - c

Question

Requirement:
Given a C program I have to identify whether the functions accessing global variables are reading them or writing them.
Example code:
#include <stdio.h>
/* global variable declaration */
int g = 20;
int main()
{
/* writing the global variable */
g = 10;
/* reading the global variable */
printf ("value of g = %d\n", g);
return 0;
}
Executing the above code I want to generate a log file in the below format:
1- Global variable a written in function main() "TIME_STAMP"
2- Global variable a read in function main() "TIME_STAMP"
Research:
I am cetainly able to acheive this by doing a static analysis of source code as per below logic:
Go through the c code and identify the statements where the global
variable is read.
Then analysis the c code statement to identify if
it is a read or write statement.(Checking if ++ or -- operator is
used with global variable or any assignemnt has been made to the
global variable)
Add a log statement above the identified statement which will execute
along with this statement execution.
This is not a proper implementation.
Some studies:
I have gone through how debuggers are able to capture information.
Some links in the internet:
How to catch a memory write and call function with address of write

Answer 1

Not completely answering your question, but to just log access you could do:
#include <stdio.h>
int g = 0;
#define g (*(fprintf(stderr, "accessing g from %s. g = %d\n", __FUNCTION__, g), &g))
void foo(void)
{
g = 2;
printf("g=%d\n", g);
}
void bar(void)
{
g = 3;
printf("g=%d\n", g);
}
int main(void)
{
printf("g=%d\n", g);
g = 1;
foo();
bar();
printf("g=%d\n", g);
}
Which would print:
accessing g from main. g = 0
g=0
accessing g from main. g = 0
accessing g from foo. g = 1
accessing g from foo. g = 2
g=2
accessing g from bar. g = 2
accessing g from bar. g = 3
g=3
accessing g from main. g = 3
g=3

Answer 2

Below is the way i solved this problem:
I created a utility(In java) which works as below(C program source file is the input to my utility):
Parse the file line by line identifying the variables and functions.
It stores global variables in a separate container and look for lines using them.
For every line which access the global variable i am analyzing them identifying whether it is a read operation or write operation(ex: ==, +=, -+
etc are write operation).
For every such operation i am instrumenting the code as suggested by #alk(https://stackoverflow.com/a/41158928/6160431) and that in turn will generate the log file when i execute the modified source file.
I am certainly able to achieve what i want but still looking for better implementation if anyone have.
For further discussion if anybody want we can have have a chat.
I refer the source code and algos from the below tools:
http://www.dyninst.org/
https://software.intel.com/en-us/articles/pin-a-dynamic-binary-instrumentation-tool