fix issue #70 about storage class v2

[tstreiff]

No description provided.

[tstreiff]

Could we discuss this?
I do not manage to interpret the failure in the report.

This bug is annoying because without fix, using a library variable like "errno" is not possible.
The first "extern int errno;" in an include file prevents the generation of the variable in an object file.

[windelbouwman]

Yes, we should discuss this! I was examining the change, and I realized I did not understand it fully, will have a close look at it. I agree that this is very annoying, since this is a very common pattern.

[windelbouwman]

Playing around a bit at this site makes it appear differently, you can declare a function as non-static after first specifying it as static.

[windelbouwman]

Rather than changing the storage class, it is probably better to change the position in the Symbol.declarations list of this declaration.

[windelbouwman]

I changed this code a bit, so that there are booleans checking for previously static or not.

[tstreiff]

Much better. It solves the "errno" issue.

I tried to test most combinations and there are 2 small problems remaining:

static int i4; // internal linkage
extern int i4; // keep internal linkage
int i4; // illegal: try to change linkage to external

Current ppci-cc accpts the 3rd line whereas it should not since it is an attempt to change linkage.
(gcc reports an error: "error: non-static declaration of ‘i4’ follows static declaration")

static void f(); // internal linkage
void void f(); // legal because for functions, no storage specifier means implicitly "extern"

Current ppci-cc correctly accepts the 2nd line which is correct, but it changes the linkage from "internal" to "external" whereas the linkage should be kept "internal" (the function "f" is declared global in the object file.
There is a subtle difference beween variables and functions there.

The C standard states:

"If the declaration of an identifier for a function has no storage-class specifier, its linkage
is determined exactly as if it were declared with the storage-class specifier extern."

and:

"For an identifier declared with the storage-class specifier extern in a scope in which a
prior declaration of that identifier is visible, if the prior declaration specifies internal or
external linkage, the linkage of the identifier at the later declaration is the same as the
linkage specified at the prior declaration."