GNU Arm Embedded Toolchain

execute only region of v8m

Asked by chiche ma

Hi,

I want to compile code for execute only region of v8m and I notice there is a GCC option "-mpure-code".
But the gcc manual of "6.2 2016q4" said this option is only available when generating non-pic code for ARMv7-M targets,
that means I can't use this option for v8m? if so, do you have any plan to support that on v8m?

Sincerely,
Terry

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Prakhar Bahuguna
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Prakhar Bahuguna (prakhar-deactivatedaccount) said : 		#1

Hi Terry,

-mpure-code is currently supported on ARMv7-M and ARMv8-M Mainline targets. It is not yet supported for ARMv8-M Baseline targets in the current release, though this may change in future.

Regards, Prakhar

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chiche ma (ccma1120180) said : 		#2

Hi Parkhar,

Thanks for your reply,
I notice there is another -mslow-flash-data have the effect of using MOV/MOVT instead of literal pools.
Though the document said "it minimized literal load for slow flash performance", I wonder is it actually 0% literal load.
Thus I could use this option as an alternative for execute-only code of V8M baseline.

Sincerely,
Terry

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Best Prakhar Bahuguna (prakhar-deactivatedaccount) said : 		#3

Hi Terry,

The purpose of -mslow-flash-data is to minimize the occurrence of literals being loaded from a slow flash memory device, but unlike -mpure-code it does not guarantee that all literal loads from a text section will be completely eliminated, and thus you cannot necessarily rely on this if you wish to place your code in execute-only memory on your target. In any case, this will not work as an alternative as -mslow-flash-data is not yet supported on ARMv8-M Baseline targets either.

Hope this helps,

Prakhar

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chiche ma (ccma1120180) said : 		#4

Thanks Prakhar Bahuguna, that solved my question.