Port 59NL server patches to 59NJ (pt. 1)

2026-05-06 08:56:22 -07:00
parent b8e7d81a22
commit a57cca6c12
6 changed files with 353 additions and 3 deletions
@@ -0,0 +1,76 @@
+# This file defines the following function:
+#   write_call_to_code(
+#     const void* patch_code,
+#     size_t patch_code_size,
+#     void* call_opcode_address,
+#     ssize_t call_opcode_bytes);
+# This function allocates memory for patch_code, copies patch_code to that
+# memory, then writes a call or jmp opcode to call_opcode_address that calls
+# the code in the allocated memory region. The allocated memory is never freed.
+# call_opcode_bytes specifies how many bytes at the callsite should be
+# overwritten. This value must be at least 5; the first 5 bytes are overwritten
+# with the call/jmp opcode itself; the rest are overwritten with nop opcodes.
+# If call_opcode_bytes is positive, a call opcode is written; if it's negative,
+# a jmp opcode is written.
+# This function pops its arguments off the stack before returning.
+
+write_call_to_code:
+  # [esp + 0x04] = code ptr
+  # [esp + 0x08] = code size
+  # [esp + 0x0C] = jump callsite
+  # [esp + 0x10] = callsite size (if zero, write the address instead of a call)
+
+  # Allocate memory for the copied code
+  mov       ecx, [0x00AA8F84]
+  push      dword [esp + 0x08]
+  mov       eax, 0x007A984C
+  call      eax  # malloc7
+  test      eax, eax
+  je        done
+
+  # Copy the code to the newly-allocated memory
+  # eax = dest pointer (from malloc7 call above)
+  mov       edx, [esp + 0x04]  # edx = source pointer
+  mov       ecx, [esp + 0x08]  # ecx = source size
+  push      ebx
+memcpy_again:
+  dec       ecx
+  mov       bl, [edx + ecx]  # Copy one byte from source to dest
+  mov       [eax + ecx], bl
+  test      ecx, ecx
+  jne       memcpy_again
+  pop       ebx
+
+  mov       edx, [esp + 0x0C]  # edx = jump callsite
+
+  # If the callsite size is zero, just write the address directly
+  cmp       dword [esp + 0x10], 0
+  jne       write_call_or_jmp
+  mov       [edx], eax
+  jmp       done
+
+  # Write the call or jmp opcode
+write_call_or_jmp:
+  lea       ecx, [eax - 5]
+  sub       ecx, edx  # ecx = (dest code addr) - (jump callsite) - 5
+  cmp       dword [esp + 0x10], 0
+  setl      al
+  or        al, 0xE8
+  mov       [edx], al  # Write E8 (call), or E9 (jmp) if size was negative
+  mov       [edx + 1], ecx  # Write delta
+
+  # Write as many nops after the call opcode as necessary
+  mov       ecx, 5
+  mov       eax, [esp + 0x10]
+  cmp       eax, 0
+  jge       write_nop_again
+  neg       eax
+write_nop_again:
+  cmp       ecx, eax
+  jge       done
+  mov       byte [edx + ecx], 0x90
+  inc       ecx
+  jmp       write_nop_again
+
+done:
+  ret       0x10