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How are inline asm statements used in GCC?
GCC provides two forms of inline asm statements. A basic asm statement is one with no operands (see Basic Asm ), while an extended asm statement (see Extended Asm) includes one or more operands. The extended form is preferred for mixing C and assembly language within a function, but to include assembly language at top level you must use basic asm .
Can you jump from ASM to C with GCC?
Jumps from asm to C labels are only supported in extended asm. Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your assembly code defines symbols or labels.
Why are ASM blocks implicitly volatile in GCC?
All basic asm blocks are implicitly volatile. This is a literal string that specifies the assembler code. The string can contain any instructions recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid assembler input.
Can a C function be an asm statement?
Extended asm statements have to be inside a C function, so to write inline assembly language at file scope (‘top-level’), outside of C functions, you must use basic asm . You can use this technique to emit assembler directives, define assembly language macros that can be invoked elsewhere in the file, or write entire functions in assembly language.
How to use inline assembly language in C code?
GCC provides two forms of inline asm statements. A basic “asm“ statement is one with no operands (see Basic Asm – Assembler Instructions Without Operands), while an extended “asm“ statement (see Extended Asm – Assembler Instructions with C Expression Operands) includes one or more operands.
Can a GCC compiler duplicate an assembly code?
Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your assembly code defines symbols or labels. Since GCC does not parse the AssemblerInstructions, it has no visibility of any symbols it references.