Common configuration methods for embedded ARM assembly optimization using GCC under Linux

Common configuration methods for using GCC for embedded ARM assembly optimization under Linux

Introduction:
In embedded systems, for ARM architecture processors, efficient optimization is often required to meet real-time requirements. Performance and resource limitations. Assembly language is a language that can directly control hardware. For some key algorithms, using assembly can greatly improve performance. This article will introduce common configuration methods for using GCC to optimize embedded ARM assembly in a Linux environment, and give relevant code examples.

1. Writing ARM assembly code
The GCC compiler supports embedded assembly. We can embed ARM assembly code in C code to optimize the performance of key functions. First, we need to write ARM assembly code.

The following is an example showing how to use ARM assembly to implement fast multiplication:

.global fast_multiply
fast_multiply:
    LDR r0, [r0]       @ load the first operand into r0
    LDR r1, [r1]       @ load the second operand into r1
    MUL r0, r0, r1     @ multiply the two operands
    BX  lr             @ return the result

The above code multiplies two numbers and returns the result.

2. Embedding ARM assembly in C code
The GCC compiler provides the feature of inline assembly, which can directly embed ARM assembly in C code. The following example shows how to embed the above fast multiplication function in C code:

int main()
{
    int a = 10;
    int b = 20;
    int result;

    asm volatile (
        "ldr r0, [%1]
"    // load the first operand into r0
        "ldr r1, [%2]
"    // load the second operand into r1
        "bl fast_multiply
"// call the fast_multiply function
        "mov %0, r0"        // save the result to "result"
        :
        :"r" (result), "r" (&a), "r" (&b)
        :"r0", "r1"         // clobbered registers
    );

    printf("Result: %d
", result);

    return 0;
}

The above code multiplies two numbers and saves the result in the variable result.

3. Compilation configuration
When using GCC to optimize ARM assembly under Linux, corresponding compilation configuration is required. The following are some common configuration methods:

1. Select ARM architecture: First, we need to specify that the GCC compiler uses the ARM architecture. You can use the -march option to specify the ARM processor architecture, for example:

$ gcc -march=armv7-a -c main.c

2. Enable optimization: The GCC compiler provides a wealth of optimization options, which can enable ARM assembly at compile time. optimization. Use the -O option to enable a certain degree of optimization, for example:

$ gcc -O2 -march=armv7-a -c main.c

3. Turn off floating point operations: For some embedded systems, there may be no floating point operation unit, so you need to specify the compiler Do not use floating point operations, you can use the -mfpu and -mfloat-abi options, for example:

$ gcc -march=armv7-a -mfpu=none -mfloat-abi=softfp -c main.c

4. Assembly optimization example
The following is a sample code that shows how to Embed ARM assembly and optimize:

#include 

int main()
{
    int a = 10;
    int b = 20;
    int result;

    asm volatile (
        "ldr r0, [%1]
"    // load the first operand into r0
        "ldr r1, [%2]
"    // load the second operand into r1
        "bl fast_multiply
"// call the fast_multiply function
        "mov %0, r0"        // save the result to "result"
        :
        :"r" (result), "r" (&a), "r" (&b)
        :"r0", "r1"         // clobbered registers
    );

    printf("Result: %d
", result);

    return 0;
}

.global fast_multiply
fast_multiply:
    LDR r0, [r0]       // load the first operand into r0
    LDR r1, [r1]       // load the second operand into r1
    MUL r0, r0, r1     // multiply the two operands
    BX  lr             // return the result

The above code multiplies two numbers and returns the result.

Conclusion:
This article introduces the common configuration methods of using GCC for embedded ARM assembly optimization in the Linux environment, and gives relevant code examples. By using the inline assembly feature of the GCC compiler, we can embed ARM assembly in C code to achieve efficient optimization for the ARM architecture. These optimizations can significantly improve the performance and efficiency of embedded systems.

Reference:

1. GNU Compiler Collection (GCC) - Using the GNU Compiler Collection (GCC), https://gcc.gnu.org/onlinedocs/
2. ARM Limited - ARM Architecture Reference Manual, https://developer.arm.com/documentation/ddi0487/latest/

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