Potential memory leak on some platforms

[dlroweht]

Hi,
There is a potential memory leak in latest version of Lua (5.4.7) and probably the other versions also. It is regarding the `va_start` that might never be ended by calling `va_end`. This can happen when calling `luaO_pushfstring` and passing it invalid format specifier, this way error gets invoked in default case of `luaO_pushvfstring` and `va_end` is never called. This "leak" might be totally irrelevant as `va_start` is a no-op on many platforms. Would calling `va_end` just before calling `luaG_runerror` be okay in this case?

[Sainan]

This is assuming there's a platform where va_* uses heap memory, because typically this would be handled via registers and the stack alone, and a Lua error being raised would either longjump or throw out of there, discarding those registers and that stack space.

-- Sainan

[Roberto Ierusalimschy]

Many thanks for the feedback. Indeed, the standard states that "Each
invocation of the va_start and va_copy macros shall be matched by a
corresponding invocation of the va_end macro in the same function."

Note the "in the same function". Currently, the call to luaG_runerror
is in another function. Moreover, it may occurr memory-allocation
errors too. So, the fix needs some care.

-- Roberto

[google.c...@passinbox.com]

Ah I see it is more complicated than what it seems especially as `luaO_pushvfstring` is used in `lua_pushvfstring` core API function. There is a cursed solution, and that is making the `luaO_pushvfstring` inline (defining it as a macro) haha, although this wouldn't prevent possible memory allocation errors to occur in case implementation uses heap to manage variable argument list, but I don't see any way to catch those kinds of errors as `va_*` functions/macros are defined to not have a return value.

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