Re: Questions on __initdata

From: Keith Owens
Date: Mon Dec 05 2005 - 23:42:24 EST

On Sun, 4 Dec 2005 15:15:33 +0100,
Jean Delvare <khali@xxxxxxxxxxxx> wrote:
>Hi all,
>I've been reading the heading comment of include/linux/init.h to learn
>when and how __initdata can be used. Some of the help text doesn't seem
>to match my observations, and some of it confused me and could probably
>be made clearer. However, I don't feel completely comfortable with this
>topic yet and would welcome comments.
>First, the comment goes:
>> /* These macros are used to mark some functions or
>> * initialized data (doesn't apply to uninitialized data)
>> * as `initialization' functions. The kernel can take this
>> * as hint that the function is used only during the initialization
>> * phase and free up used memory resources after
>My tests (on i386) seem to suggest that "doesn't apply to uninitialized
>data" only holds for non-global variables. Tagging uninitialized global
>variables __initdata works, and moves the variables from .bss to .data.
>Is it correct? Does it work on all archs? If so, the comment above
>needs to be fixed.

gcc version dependent. Older versions of gcc put all uninitialized
global variables into .bss, even if there was an attribute like
__initdata that tried to use a different section. So we got into the
habit of '__initdata variables must be explicitly initialized'. Some
platforms are using old versions of gcc where that restriction may
still apply.

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