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-mcmse
Enables the generation of code for the Secure state of the ARMv8-M Security Extensions. This option is required when creating a Secure image.
Note
ARMv8-M Security Extensions are not supported when building Read-Only Position-Independent (ROPI) and Read-Write Position-Independent (RWPI) images.Usage
Specifying -mcmse targets the Secure
state of the ARMv8-M Security Extensions. The following are available:
- The Test Target,
TT, instruction. TTinstruction intrinsics.- Non-secure function pointer intrinsics.
__attribute__((cmse_nonsecure_call))and__attribute__((cmse_nonsecure_entry))function attributes.
Note
- The value of the
__ARM_FEATURE_CMSEpredefined macro indicates what ARMv8-M Security Extension features are supported. - Compile
Secure code with the maximum capabilities for the target. For
example, if you compile with no FPU then the Secure functions do not
clear floating-point registers when returning from functions
declared as
__attribute__((cmse_nonsecure_entry)). Therefore, the functions could potentially leak sensitive data. - Structs with undefined bits caused by padding and half float are currently unsupported as arguments and return values for Secure functions. Using such structs might leak sensitive information. Structs that are large enough to be passed by pointer are also unsupported and produce an error.
-
The following cases are not supported when compiling with
-mcmseand give an error:- Variadic entry functions.
- Entry functions with arguments that do not fit in registers, because there are either many arguments or the arguments have large values.
- Non-secure function calls with arguments that do not fit in registers, because there are either many arguments or the arguments have large values.
Example
This example shows how to create a Secure image using an input import
library, oldimportlib.o, and a scatter file, secure.scat:
armclang --target=arm-arm-none-eabi -march=armv8m.main -mcmse secure.c -o secure.o armlink secure.o -o secure.axf--import-cmse-lib-outimportlib.o--import-cmse-lib-inoldimportlib.o--scattersecure.scat
armlink also generates the Secure
code import library, importlib.o that is required
for a Non-secure image to call the Secure image.