Re: Linux 2.2.20-pre4

[Philip Blundell]

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>> It wont build with gcc 3.0 yet. To start with gcc 3.0 will assume it can
>> insert calls to 'memcpy'
>
>IMHO omitting -fno-builtin when compiling the kernel was always a risky
>proposition...  Since we provide our own copies of many of the builtins
>[which are used in the kernel] anyway... why not always -fno-builtin,
>and then call __builtin_foo when we really want the compiler's version..
>
>gcc 3.0 without -fno-builtin is perfectly allowed to assume it can
>insert calls to memcpy..

I don't think -fno-builtin has any bearing on whether gcc will emit calls to 
memcpy; instead it prevents gcc from open-coding them when it thinks it 
understands what's going on.

Try this with gcc -O2 -S, and again with -fno-builtin:

struct s { int a[200]; };

f(struct s *a, struct s *b)
{
  *b = *a;
}

g(int *a, int *b)
{
  memcpy(b, a, 4);
}

p.

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