Posted in
6449
12:25 pm, December 12, 2021
Hello world in C and seeing what it is actually doing
One of the most simple C applications, how to compile it and how to objdump it.
C
#include
int main()
{
int i;
for(i=0;i < 10; i++)
{
puts("Hello Mac\n");
}
return 0;
}
This will return the string Hello Mac
10 times.
lets compile and run it
gcc firstprog.c
ls -l
./a.out
now see what its really doing
objdump -D a.out | grep -A20 main.:
Random Fact about 32 vs 64 bit processors.
32-bit processors have 232 (or 4,294,967,296) possible addresses
64-bit ones have 264 (1.84467441 x 1019) possible addresses
Each byte is shown in hexadecimal notation which is a base 16 numbering system, rather than the normal system we are used to which is base-10. Hex uses 0 - 9 and also A - F for 10 - 15.
Show what it would look like with intel formatting
objdump -M intel -D a.out | grep -A20 main.:
Note this will throw an error on arm based mac's, for obvious reasons.
objdump: error: 'a.out': Unrecognized disassembler option: intel
.
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