What is the use of pragma code section and data section?

Question

What exactly will happen to the data segment and text segment if I use the below two lines in my c source code file?

#pragma CODE_SECTION(func1, "Sec1")
#pragma DATA_SECTION(globalvar1, "Sec2")

Solution 1

Source (contains examples): https://web.archive.org/web/20080803190119/http://hi.baidu.com/jevidyang/blog/item/6d4dc436d87e3a300b55a918.html

Note: #pragma is compiler specific, so syntax may vary for your compiler.

The DATA_SECTION pragma allocates space for the symbol in a section called section name. The syntax for the pragma in C could be:

#pragma DATA_SECTION (symbol, "section name");

The syntax for the pragma in C++ could be:

#pragma DATA_SECTION ("section name");

The DATA_SECTION pragma is useful if you have data objects that you want to link into an area separate from the .bss section.

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The CODE_SECTION pragma allocates space for the func in a section named section name. The CODE_SECTION pragma is useful if you have code objects that you want to link into an area separate from the .text section. The syntax of the pragma in C could be:

#pragma CODE_SECTION (func, "section name")

The syntax of the pragma in C++ could be:

#pragma CODE_SECTION ("section name")

Solution 2

#pragma means "here follows something implementation-defined unique to this compiler". So what will happen depends on the compiler you are using. If the compiler doesn't support this specific pragma, the whole thing will be ignored.

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In this case it is fairly obvious, however.

#pragma CODE_SECTION(func1, "Sec1") means: "func1 should be in program memory, in the memory area called Sec1". Sec1 will be a read-only memory location where the actual code of func1 will be allocated.

#pragma DATA_SECTION(globalvar1, "Sec2") means: "globalvar1 should be in data memory, in the memory area called Sec2". Sec2 will be a read/write location where the variable globalvar1 will be allocated.

Comments

[Lundin]

There is no such thing as "the syntax for this in C/C++ is..."! DATA_SECTION and CODE_SECTION are completely compiler-specific and not supported by any standard at all. What will happen is up to the compiler. I know several compilers that support CODE_SECTION and DATA_SECTION but with a completely different syntax.

[user247702]

If I change is to could be, will you remove the downvote then? Of course #pragma is compiler specific.

[Lundin]

Yes, I suppose that is better. The important thing is not to trick anyone into thinking that this is well-defined by some standard. Though of course the original question is lacking, as there was no specific compiler mentioned.

[rashok]

Whether #pragama CODE_SECTION is same as #pragma code_seg which is supported in vc. msdn.microsoft.com/en-us/library/s20kdbse(v=vs.71).aspx

[Lundin]

@rajaashok Was that a question or a statement? Any actual reason for downvote, or did you just feel like it?