Add macro to check if pointer points into array

src/check_bounds.asm

@@ -0,0 +1,46 @@
+_check_bounds:
+    ; check_bounds [rax] [rdi] [rsi] [rdx]
+    ;  rax = pointer to check
+    ;  rdi = array
+    ;  rsi = element size (in bytes)
+    ;  rdx = array size (in elements)
+    push_registers
+
+    ; rcx size of array in bytes
+    mov rcx, rdx
+    imul rcx, rsi
+    ; rbx is end of array
+    mov rbx, rdi
+    add rbx, rcx
+
+._check_bounds_check_oob_left:
+    cmp rax, rdi
+    jl ._check_bounds_oob_left
+
+._check_bounds_check_oob_right:
+    ; todo: is this jg or jge?
+    cmp rax, rbx
+    jg ._check_bounds_oob_right
+
+
+._check_bounds_check_element_align:
+
+    jmp ._check_bounds_end
+._check_bounds_oob_left:
+    puts  "[error] array pointer out of bounds. (pointer too low)"
+    jmp ._check_bounds_error
+
+._check_bounds_oob_right:
+    puts  "[error] array pointer out of bounds. (pointer too high)"
+    jmp ._check_bounds_error
+
+._check_bounds_error:
+    printlnf "         pointer: %p", rax
+    printlnf "     array start: %p", rdi
+    printlnf "       array end: %p", rbx
+    exit 1
+
+._check_bounds_end:
+    pop_registers
+    ret
+

src/macros.asm

@@ -1,3 +1,27 @@
+%macro check_bounds 4
+    ; check_bounds [ptr into array] [array] [element size in bytes] [array size in elements]
+    push rbp
+
+    mov rbp, rsp
+    sub rsp, 32
+
+
+    mov qword [rbp-32], %1
+    mov qword [rbp-24], %2
+    mov qword [rbp-16], %3
+    mov qword [rbp-8], %4
+
+    mov rax, [rbp-32]
+    mov rdi, [rbp-24]
+    mov rsi, [rbp-16]
+    mov rdx, [rbp-8]
+    call _check_bounds
+
+    mov rsp, rbp
+
+    pop rbp
+%endmacro check_bounds
+
 %macro str_to_stack 1
     ; str_to_stack [fixed str]
     ; returns into rax a pointer to the stack

src/teeworlds_asmr.asm

@@ -124,6 +124,7 @@ section .text
 %include "src/printf.asm"
 %include "src/logger.asm"
 %include "src/hex.asm"
+%include "src/check_bounds.asm"
 %include "src/terminal.asm"
 %include "src/udp.asm"
 %include "src/packer.asm"

tests/array_oob_test.asm

@@ -0,0 +1,9 @@
+%include "tests/assert.asm"
+
+_start:
+    ; rax is pointer to 2nd element in the array
+    mov rax, huff_nodes
+    add rax, HUFF_CNODE_SIZE
+    check_bounds rax, huff_nodes, HUFF_CNODE_SIZE, HUFFMAN_MAX_NODES
+    exit 0
+

tests/assert.asm

@@ -47,6 +47,7 @@ section .text
 %include "src/printf.asm"
 %include "src/logger.asm"
 %include "src/hex.asm"
+%include "src/check_bounds.asm"
 %include "src/udp.asm"
 %include "src/packer.asm"
 %include "src/packet.asm"