Why does this give me a segfault

[StackMasher]

I'm learning amd64 assembly (gas syntax) and I'm trying to write a hello world program based on this, but when I run it I get a segmentation fault. Here's the code:

.data
   str:
     .ascii "Hello World!\n"
.text
   .globl main
   .extern printf
   main:
     movq str,%rdi
     call printf
     ret

 

[Maq47]

Does gas syntax even recognize regex? If not, you should replace '\n' with '\12'. If you are running the code as a .s file, the 3rd line would need to read as follows:

     .ascii "Hello World!\12\0"

This is because ASCII strings in a C routine need to be null terminated, hence the '\0'. Apply this fix, then tell me if it works.

 

[StackMasher]

Does gas syntax even recognize regex? If not, you should replace '\n' with '\12'. If you are running the code as a .s file, the 3rd line would need to read as follows:

     .ascii "Hello World!\12\0"

This is because ASCII strings in a C routine need to be null terminated, hence the '\0'. Apply this fix, then tell me if it works.

I explicitly null terminated it like you said and the segfault is still there

.data
   str:
     .ascii "Hello World!\12\0"
.text
   .globl main
   .extern printf
   main:
     movq str,%rdi
     call printf
     ret

 

[sarkwalvein]

Just checking, but are you using Linux or Windows?

 

[StackMasher]

Just checking, but are you using Linux or Windows?

Linux

 

[memcpy]

Try with lea (change movq), printf takes an address to string. Because you don't pass variable args list you need to zero rax.