building kernel with -O

[Xin Tong]

why can not __builtin_return_address() be made *never* inline and use
current level+1 to get the return address of the function of interest.  For
any stack introspection, having 1 more level will not hurt functionality.

given its explanation below

— Built-in Function: void * *__builtin_return_address* (unsigned int level)

This function returns the return address of the current function, or of one
of its callers. The level argument is number of frames to scan up the call
stack. A value of 0 yields the return address of the current function, a
value of 1 yields the return address of the caller of the current function,
and so forth. When inlining the expected behavior is that the function
returns the address of the function that is returned to. To work around
this behavior use the noinline function attribute.




On Wed, Jul 30, 2014 at 11:18 AM, <Valdis.Kletnieks at vt.edu> wrote:

> On Wed, 30 Jul 2014 09:03:38 -0500, Xin Tong said:
>
> > Ive heard that one can not build the entire Linux kernel with -O0 option.
> > why is that ? being a compiler developer, i can not think of reasons why
> > that is the case.
>
> The short answer:  -O0 completely suppresses function inlining, and there
> are several places where the kernel depends on inlining for correct
> operation (most notably with things like __builtin_return_address()
> and friends for introspecting the stack, but there's a few other
> corner cases I can't remember at the moment...)
>
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