How do you recognize sscanf input parsing in assembly?

Look for several lea offset(%rsp), %reg instructions (the output pointers), a format-string address in %esi, then call <sscanf> and a check on the return count.

* Several lea offset(%rsp),%reg build output pointers, %esi holds the format string (read with x/s), then call and a cmp on %eax (items parsed). Slot offsets reveal each field's size. *

lea  0x8(%rsp), %r8
lea  0x7(%rsp), %rcx
lea  0xc(%rsp), %rdx
mov  $0x4024de, %esi
mov  %rbx, %rdi
mov  $0x0, %eax
call <sscanf>
cmp  $0x2, %eax
jg   ok_label

How to read it:

1. %rdi = input string (1st argument)
2. %esi = format string address (2nd argument) — examine with x/s
3. %rdx, %rcx, %r8, ... = pointers to where parsed values are stored
4. Return value in %eax = number of items successfully parsed
5. The cmp after checks if enough items were parsed

Examine the format string:

(gdb) x/s 0x4024de
"%d %c %d"

Stack layout tip: The lea offsets tell you where each value lives on the stack and its size (1 byte for %c, 4 bytes for %d).

Go deeper:

• C stdio — scanf/sscanf family (Wikipedia) — Documents the sscanf format specifiers and the return value (count of items parsed) that the cmp checks.
• Stack frame layout on x86-64 (Eli Bendersky) — Explains the argument registers (%rdi,%rsi,%rdx,%rcx,%r8) and stack-slot addressing behind the lea output pointers.