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Compiler User Guide

Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler Coding Practices Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler support for inline assembly language Inline assembler support in the compiler Restrictions on inline assembler support in the co Inline assembly language syntax with the __asm key Inline assembly language syntax with the asm keywo Inline assembler rules for compiler keywords __asm Restrictions on inline assembly operations in C an Inline assembler register restrictions in C and C+ Inline assembler processor mode restrictions in C Inline assembler Thumb instruction set restriction Inline assembler Vector Floating-Point (VFP) restr Inline assembler instruction restrictions in C and Miscellaneous inline assembler restrictions in C a Inline assembler and register access in C and C++ Inline assembler and the # constant expression spe Inline assembler and instruction expansion in C an Expansion of inline assembler instructions that us Expansion of inline assembler load and store instr Inline assembler effect on processor condition fla Inline assembler expression operands in C and C++ Inline assembler register list operands in C and C Inline assembler intermediate operands in C and C+ Inline assembler function calls and branches in C Inline assembler branches and labels in C and C++ Inline assembler and virtual registers Embedded assembler support in the compiler Embedded assembler syntax in C and C++ Effect of compiler ARM and Thumb states on embedde Restrictions on embedded assembly language functio Compiler generation of embedded assembly language Access to C and C++ compile-time constant expressi Differences between expressions in embedded assemb Manual overload resolution in embedded assembler __offsetof_base keyword for related base classes i Compiler-supported keywords for calling class memb __mcall_is_virtual(D, f) __mcall_is_in_vbase(D, f) __mcall_offsetof_vbase(D, f) __mcall_this_offset(D, f) __vcall_offsetof_vfunc(D, f) Calling nonstatic member functions in embedded ass Calling a nonvirtual member function Calling a virtual member function Accessing sp (r13), lr (r14), and pc (r15) Differences in compiler support for inline and emb Compiler Command-line Options Language Extensions Compiler-specific Features C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Inline assembler instruction restrictions in C and C++ code

6.12 Inline assembler instruction restrictions in C and C++ code

There are a number of instructions that the inline assembler does not support.

Specifically, the following instructions are not supported:
  • BKPT, BX, BXJ, and BLX instructions.

    Note

    You can insert a BKPT instruction in C and C++ code by using the __breakpoint() intrinsic.
  • LDR Rn, =expression pseudo-instruction. Use MOV Rn, expression instead. (This can generate a load from a literal pool.)
  • LDRT, LDRBT, STRT, and STRBT instructions.
  • MUL, MLA, UMULL, UMLAL, SMULL, and SMLAL flag setting instructions.
  • MOV or MVN flag-setting instructions where the second operand is a constant.
  • The special LDM instructions used in system or supervisor mode to load the user-mode banked registers, written with a ^ after the register list, such as:
    LDMIA sp!, {r0-r12, lr, pc}^
    
  • ADR and ADRL pseudo-instructions.

    Note

    You can use MOV Rn, &expression; instead of the ADR and ADRL pseudo-instructions.
  • ARM recommends not using the LDREX and STREX instructions. This is because the compiler might generate loads and stores between LDREX and STREX, potentially clearing the exclusive monitor set by LDREX. This recommendation also applies to the byte, halfword, and doubleword variants LDREXB, STREXB, LDREXH, STREXH, LDREXD, and STREXD.
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