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From: "mbuilov at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/46045] incorrect code generated if redecalring local variable in do-while(0)
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Date: Sun, 17 Oct 2010 16:19:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46045

--- Comment #4 from Michael Builov <mbuilov at gmail dot com> 2010-10-17 16:19:37 UTC ---
Just a warning with -Wextra, but no warnings with -Wall -pedantic.

I found a bug with this code:

struct A {
        int k;
        int m;
};

#define dump(_a_) \
        do { \
                struct A *a = _a_; \
                printk("%d, %d\n", a->k, a->m); \
        } while (0)

void foo(struct A *b, struct A *a)
{
        dump(b); /* fine */
        dump(a); /* crash */
}

This code compiles and runs fine with Sun cc, but crashes with gcc.

I think it is definitely a bug in gcc, this code compiled only with extra
warnings (not enabled by default in linux kernel) should not crash.

The best way to fix this issue - generate an error message, like when
redeclaring variable in function:

void bar(struct A *a)
{
        struct A *a = a; /* error: 'a' redeclared as different kind of symbol
*/
}

strange, but no errors/non-extra warnings with:

void bar(struct A *a)
{
        {
                struct A *a = a;
        }
}