Re: [Error after setting -Og] â__bad_copy_fromâ declared with attribute error: copy source size is too small

From: Al Viro
Date: Fri Nov 17 2017 - 22:15:44 EST

On Thu, Nov 09, 2017 at 04:02:53PM -0500, Wei Wei wrote:
> Hi all,
> I get a compile time error after setting -Og when compiling for the latest GitHub version.
> I am using `make defconfigâ to get the default x86_64 config. But previously I did this in v4.4,
> it's fine.

; cat >a.c <<'EOF'
extern void __attribute((error("1"))) f1(void);
extern void __attribute((error("2"))) f2(void);

static inline __attribute__((always_inline)) void bar(const void *addr)
int sz = __builtin_object_size(addr, 0);
if (__builtin_expect(sz >= 0, 0))
if (sz >= 0)

void foo(int *in)
; gcc -O2 -c a.c
; gcc -Og -c a.c
In function âbarâ,
inlined from âfooâ at a.c:15:2:
a.c:8:3: error: call to âf1â declared with attribute error: 1

Note that the call of f2() _was_ eliminated. Wrap the condition into
__builtin_expect() and with -Og it doesn't get eliminated until too
late. It's really brittle and dependent not just upon the _result_
of optimizations (get rid of __attribute((error())) in those and
you'll see that with -Og it compiles into
.file "a.c"
.globl foo
.type foo, @function
rep ret
.size foo, .-foo
getting rid of both calls, as it ought to); it depends upon the moment
when dead code elimination happens. -Og leaves the sucker around for
too long. If you replace that __builtin_object_size() with -1 (which
is what it evaluates to), you'll get elimination happening early enough
even with -Og; ditto for getting rid of inlining...