push instruction.. push %rbx

| push instruction | (gdb) disass Dump of assembler code for function _IO_default_uflow: 0x00007f7c1e9964d0 : mov 0xd8(%rdi),%rax => 0x00007f7c1e9964d7 : push %rbx 0x00007f7c1e9964d8 : mov %rdi,%rbx 0x00007f7c1e9964db : callq *0x20(%rax) 0x00007f7c1e9964de : cmp $0xffffffffffffffff,%eax 0x00007f7c1e9964e1 : je 0x7f7c1e9964f2 0x00007f7c1e9964e3 : mov 0x8(%rbx),%rdx 0x00007f7c1e9964e7 : movzbl (%rdx),%eax 0x00007f7c1e9964ea : add $0x1,%rdx 0x00007f7c1e9964ee : mov %rdx,0x8(%rbx) 0x00007f7c1e9964f2 …