* [Error after setting -Og] ‘__bad_copy_from’ declared with attribute error: copy source size is too small
@ 2017-11-09 21:02 Wei Wei
2017-11-18 3:03 ` Al Viro
0 siblings, 1 reply; 2+ messages in thread
From: Wei Wei @ 2017-11-09 21:02 UTC (permalink / raw)
To: LKML
Hi all,
I get a compile time error after setting -Og when compiling for the latest GitHub version.
I am using `make defconfig’ to get the default x86_64 config. But previously I did this in v4.4,
it's fine.
Modification to Makefile:
KBUILD_CFLAGS += -O2 $(call cc-disable-warning,maybe-uninitialized,)
else
-KBUILD_CFLAGS += -O2
+KBUILD_CFLAGS += -Og
endif
endif
And error info:
In file included from ./arch/x86/include/asm/preempt.h:6:0,
from ./include/linux/preempt.h:80,
from ./include/linux/rcupdate.h:40,
from ./include/linux/rculist.h:10,
from ./include/linux/pid.h:4,
from ./include/linux/sched.h:13,
from kernel/ptrace.c:12:
In function ‘check_copy_size’,
inlined from ‘copy_to_user’ at ./include/linux/uaccess.h:153:6,
inlined from ‘ptrace_request’ at kernel/ptrace.c:934:7:
./include/linux/thread_info.h:138:4: error: call to ‘__bad_copy_from’ declared
with attribute error: copy source size is too small
__bad_copy_from();
^
scripts/Makefile.build:313: recipe for target 'kernel/ptrace.o' failed
make[1]: *** [kernel/ptrace.o] Error 1
Makefile:1023: recipe for target ‘kernel' failed
Any help is appreciated!
Thank you,
Wei
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [Error after setting -Og] ‘__bad_copy_from’ declared with attribute error: copy source size is too small
2017-11-09 21:02 [Error after setting -Og] ‘__bad_copy_from’ declared with attribute error: copy source size is too small Wei Wei
@ 2017-11-18 3:03 ` Al Viro
0 siblings, 0 replies; 2+ messages in thread
From: Al Viro @ 2017-11-18 3:03 UTC (permalink / raw)
To: Wei Wei; +Cc: LKML
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 defconfig’ 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))
f1();
if (sz >= 0)
f2();
}
void foo(int *in)
{
bar(in);
}
EOF
; gcc -O2 -c a.c
; gcc -Og -c a.c
In function ‘bar’,
inlined from ‘foo’ at a.c:15:2:
a.c:8:3: error: call to ‘f1’ declared with attribute error: 1
f1();
^
;
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"
.text
.globl foo
.type foo, @function
foo:
.LFB1:
.cfi_startproc
rep ret
.cfi_endproc
.LFE1:
.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...
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