On 10.06.21 05:40, Ni, Ray wrote:
Without the ParseStatus field, callee cannot know whether ParseElfImage()
is called.
It can by function contracts, the caller guarantees it. I.e. with the PE
library I linked, no other function must be called before the init function.
Your "ParseElfImage" function is very similar. The context is
initialized by it, i.e. it is trash if it is not called, i.e. it must be
called before other functions.
If it is called, which we know, the caller has the return status. For
PE, it means the caller must not proceed with any further PE processing
and abort immediately.
Is there any scenario where this does not work for ELF? Sorry if I
missed something.
Caller might call LoadElfImage() without firstly calling ParseElfImage() by
mistake.
ParseStatus is added to catch such mistake.
If ParseElfImage() is not called, nothing will initialize ParseStatus
and the load function will read random data. If AllocateZeroPool was
used for the context, a common pattern throughout the codebase to harden
against memory initialization bugs, it would even report success at all
times anyway. Sorry, but I think this is dead code.
Maybe for some context, my main issue at first was that the checks are
all proper runtime checks with no ASSERTs at all, so I got confused how
this situation could happen in a realistic scenario. I needed to trace
the ParseStatus data flow to understand the idea is basically the same
as in the PE library. Code in a way is self-documenting, and this
personally gave me a hard time understanding why it is written this way.
But thanks for clarifying your intention! :)
Best regards,
Marvin
I don't trust the caller would follow the contracts properly😊.
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