6.4. Differences between inline and embedded assembly code

There are differences between the way inline and embedded assembly is compiled:

Table 6.1 summarizes the main differences between inline assembler and embedded assembler.

Table 6.1. Differences between inline and embedded assembler

FeatureEmbedded assemblerInline assembler
Instruction setARM and Thumb.ARM only.
ARM assembler directivesAll supported.None supported.
ARMv6 instructionsAll supported.

Supports only the media instructions.

C/C++ expressionsConstant expressions only.Full C/C++ expressions.
Optimization of assembly codeNo optimization.Full optimization.
InliningNever.Possible.
Register accessSpecified physical registers are used. You can also use PC, LR and SP.

Uses virtual registers (see Virtual registers). Using sp (r13), lr (r14), and pc (r15) gives an error. See Legacy inline assembler that accesses sp, lr, or pc.

Return instructionsYou must add them in your code.Generated automatically. (The BX , BXJ, and BLX instructions are not supported.)
BKPT instructionSupported directly.Not supported.

See also Differences between expressions in embedded assembly and C or C++.

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