#; Demonstration of using GAS CFI directives. #; Michal Ludvig <michal@logix.cz> #; http://www.logix.cz/michal/devel/gas-cfi #; $ as -o test.o gas-cfi-test.s && gcc -nostdlib -o test test.o .text #; func_locvars #; - function with a space on the stack #; allocated for local variables .type func_locvars,@function func_locvars: .cfi_startproc #; alocate space for local vars sub $0x1234,%rsp .cfi_adjust_cfa_offset 0x1234 #; dummy body movl $1,%eax #; release space of local vars and return add $0x1234,%rsp .cfi_adjust_cfa_offset -0x1234 ret .cfi_endproc #; func_prologue #; - functions that begins with standard #; prologue: "pushq %rbp; movq %rsp,%rbp" .type func_prologue,@function func_prologue: .cfi_startproc #; prologue, CFI is valid after #; each instruction. pushq %rbp .cfi_def_cfa_offset 16 .cfi_offset rbp,-16 movq %rsp, %rbp .cfi_def_cfa_register rbp #; function body call func_locvars addl $3, %eax #; epilogue with a valid CFI #; (we're better than gcc :-) leaveq .cfi_def_cfa rsp,8 ret .cfi_endproc #; func_otherreg #; - function that moves frame pointer to #; another register (r12) and then allocates #; a space for local variables .type func_otherreg,@function func_otherreg: .cfi_startproc #; save frame pointer to r12 movq %rsp,%r12 .cfi_def_cfa_register r12 #; alocate space for local vars #; (no .cfi_{def,adjust}_cfa_offset here, #; because CFA is computed from r12!) sub $100,%rsp #; function body call func_prologue addl $2, %eax #; restore frame pointer from r12 movq %r12,%rsp .cfi_def_cfa_register rsp ret .cfi_endproc #; main #; - typical function .type main,@function main: .cfi_startproc #; only function body that doesn't #; touch the stack at all. call func_otherreg #; return ret .cfi_endproc #; _start #; - standard entry point .type _start,@function .globl _start _start: .cfi_startproc call main movq %rax,%rdi movq $0x3c,%rax syscall hlt .cfi_endproc