Why gcc place a large constant array to ".rwdata" section rather than ".rodata" section?

1
votes
/* 0xFFFFFFFF * 256*/
#define test_256X0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, ... 0xFFFFFFFF

After compiling, the const array is placed in ".rwdata" section rather than ".rodata" section, and I don't know why.

After google and searching the stackoverflow site, there is no specified answer. Does any one know why or how to ask compiler(or linker) to output warning message when "placing constant data into non-read-only section"? thanks.

PS. I resolve my problem by add attribure((section(".rodata")))

__attribure__((section(".rodata"))) volatile const int TEST_ro[512] = {test_256X, test_256X};

PS. I use linaor-gcc compiler for arm core

1
cgcclinaro
Why do you declare it volatile? What happens if you don't? - rici
What you have there declares an array of volatile const int. Why would a const need to be volatile? - T.J. Crowder
That's not what volatile is for. It indicates to the compiler that the memory may be changed asynchronously so it doesn't used cached results. It's inconsistent with const. Try static which tells the compiler that other modules cannot access it. - luser droog
@luserdroog const is not necessarily inconsistent with volatile. const doesn't mean variable cannot change, it means it cannot be changed. - user694733
Why do you need to place the array in .rodata section? - Nikolai

1 Answers

1
votes

Answer: If I want a variable to be "volatile" and place in read-only section, use

__attribute__((section(".rodata"))) /* default read-only data section*/

is the best way.

reference:

  1. That's not what volatile is for. It indicates to the compiler that the memory may be changed asynchronously so it doesn't used cached results. It's inconsistent with const. Try static which tells the compiler that other modules cannot access it. – luser droog

  2. If want to place variable to specific section, then using the explicit section placement is the way to go. C standard gives very limited set of tools for this, so you are at the mercy of what compiler provides. attribute is not pretty, but it's most likely what you need to do.