在x86汇编中使用标志寄存器作为布尔返回值是否属于不良实践？

Great question—this is one of those classic assembly style tradeoffs that hinges on context, so let’s break down the pros, cons, and when each approach makes sense.

First, let’s clarify: using the Zero Flag (ZF) to signal a boolean result isn’t inherently a bad practice. In fact, it’s a common, efficient pattern in many low-level x86 codebases:

• Efficiency: Most x86 instructions that check conditions (like cmp, test) already set ZF as a side effect. If your function’s core logic is a comparison or test, returning via ZF avoids extra instructions to move a 0/1 into AX. For example, your is_value_correct routine could look like this and be perfectly clean:

  is_value_correct:
      cmp ecx, [expected_value]  ; Check if input matches expected
      ret                        ; ZF is set based on the comparison result
  

  No redundant mov operations—just straight-up leveraging the flag that’s already being set anyway.
• Legacy/System Code Compatibility: A lot of older BIOS routines, kernel-level code, and even some standard library assembly implementations use flags to return status. If you’re working in that ecosystem, following this pattern keeps your code consistent with existing conventions.

That said, the coding standard recommendation to use AX for simple values isn’t arbitrary either—there are good reasons to prefer it in many cases:

• Consistency & Maintainability: In larger teams or projects, having a single convention (like "all functions return scalar values in AX/EAX") eliminates cognitive overhead. No one has to memorize which functions use flags vs. registers, which reduces bugs from misremembering calling semantics.
• Interoperability with High-Level Languages: If your assembly needs to interface with C/C++ code, standard calling conventions (like cdecl, stdcall) specify that integer/boolean return values go in EAX. Using ZF would require extra glue code to translate the flag into a register value, which adds complexity.
• Flexibility: If your function might need to return more than a simple boolean later (e.g., an error code with multiple states), using AX gives you room to expand without rewriting the calling logic. Flags have limited bits to work with, so they’re less adaptable to future changes.

So, Should You Use ZF or AX? #

It depends:

• Use ZF if: You’re writing performance-critical code, working in a legacy/system context where flag-based returns are standard, or building small, self-contained routines where efficiency trumps cross-compatibility.
• Use AX if: You’re following a team coding standard, need to interface with high-level languages, or want your code to be easily maintainable and extensible.

Neither approach is "bad"—it’s all about matching the style to your project’s needs.

内容的提问来源于stack exchange，提问作者Trap