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flat assembler > Windows > local varialbles - stack vs .data section

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int0x50



Joined: 19 Jul 2019
Posts: 13
how do you manage variables within a function? you keep everything in one .data section or you manage through altering esp?
Post 07 Aug 2019, 08:56
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bitRAKE



Joined: 21 Jul 2003
Posts: 2795
Location: dank orb
Re-entrant code requires keeping the data local, or allocating space: recursion, multi-threaded, etc. Code re-use can benefit from keeping the data local (feels more encapsulated, just copying the code into any project and use it).

Global data is needed for visibility throughout the program, and for persistence throughout execution.

Most software needs a combination of the two approaches.

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Post 07 Aug 2019, 10:29
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DimonSoft



Joined: 03 Mar 2010
Posts: 572
Location: Belarus
int0x50 wrote:
how do you manage variables within a function? you keep everything in one .data section or you manage through altering esp?

There’re such words as prologue and epilogue, and the idea behind them is so widely used that it even got into a standard set of procedure macros shipped with FASM. EBP is also there for a reason.
Post 07 Aug 2019, 16:56
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ProMiNick



Joined: 24 Mar 2012
Posts: 356
Location: Russian Federation, Sochi
Until thou got stack overload error thou could keep variables anywhere. In case of growing functional of thour program (stack use) thou will have to start to economy stack resources.
In multythreading app thou will need to economy stack on needs not relative to current thread. Because stack is place for threadvars.
Post 07 Aug 2019, 17:33
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 16782
Location: In your JS exploiting you and your system
When deciding between global vs local variables I like to think of global variables the same way as files on a disk. If the data makes sense to be stored in a file then it can also make sense to make it global. Otherwise store it locally.

But locally doesn't always have to be on the stack. If you have a large local data set then you can also allocate memory and store it there. And remember to free it before returning to the caller.
Post 07 Aug 2019, 17:39
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guignol



Joined: 06 Dec 2008
Posts: 620
Location: I mean good, I know better, only us will do best
ok
Post 07 Aug 2019, 17:40
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