On Aug 21, 2006, at 19:13:20, Andi Kleen wrote:
What's the problem with adding -ffreestanding and stating
explicitely which functions we want to be handled be builtins, and
which functions we don't want to be handled by builtins?
Take a look at lib/string.c and think about it a bit.
So why can't lib/string.c explicitly say __builtin_foo() instead of
foo() where we mean the former? Here's a brief summary:
With -ffreestanding:
__builtin_foo(): Use the GCC built-in if possible, otherwise out-
of-line
foo(): Always use the out-of-line function
Without -ffreestanding:
__builtin_foo(): Use the GCC built-in if possible, otherwise out-
of-line
foo(): Use the GCC built-in if possible, otherwise out-
of-line
What's wrong with always specifying -ffreestanding and using
__builtin_foo() instead of foo() where applicable? That's what it
was designed for, according to the GCC manual:
http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/C-Dialect-Options.html#C-
Dialect-Options
If you want to unconditionally force a certain function to use the
GCC built-in on a particular architecture, you could always just do
this to get exactly the same result as without -ffreestanding:
#define memcpy(dest, src, len) __builtin_strcpy((dest), (src), (len))
#define memcmp(a, b, len) __builtin_strcmp((a), (b), (len))
[...]
Just stuff those types of defines in an x86-64 specific header
somewhere and turn on -ffreestanding unconditionally; you'll fix all
of the problems with MIPS, etc, without even changing the semantics
on x86-64.
Cheers,
Kyle Moffett
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