Does printf require additional stack space on the x86-64?
assembly, printf, x86, x86-64
Solution
The stack must be 16-byte aligned, according to the www.x86-64.org/documentation/abi.pdf and also Microsoft's http://msdn.microsoft.com/en-us/library/ms235286(v=vs.80).aspx
Problem
While I know it is best to use compiler intrinsics, and for that matter, `printf_chk`, and also to put data in `.rodata` sections, I'm looking at gaining a deeper understanding of assembly language and am interested in compact code. There is something about `printf` I don't understand. I know where to put the parameters, and I know how to use `%al` for varargs, but it appears to be requiring additional stack space that I cannot account for. This short program ``` .text .globl main main: movsd value(%rip), %xmm0 # value to print movl $format, %edi # format string movl $1, %eax # one floating-point arg call printf movl $0, %eax # return 0 from main ret .align 8 value: .double 74.321 format: .asciz "%g\n" ``` gives a segfault. However, when I add additional stack space to the frame, it works fine: ``` .text .globl main main: subq $8, %rsp # ADD SOME STACK SPACE TO FRAME (WHY?) movsd value(%rip), %xmm0 # value to print movl $format, %edi # format string movl $1, %eax # one floating-point arg call printf movl $0, %eax # return 0 from main addq $8, %rsp # REMOVE ADDED STACK SPACE ret .align 8 value: .double 74.321 format: .asciz "%g\n" ``` Could it be an alignment issue? (I get the same problem when `value` and `format` are in an `.rodata` section.)