* [PATCH v2] compiler.h: Don't use compile-time assert when __NO_INLINE__ is defined
@ 2020-02-05 14:15 Zenghui Yu
2020-02-16 3:21 ` Richard Henderson
0 siblings, 1 reply; 2+ messages in thread
From: Zenghui Yu @ 2020-02-05 14:15 UTC (permalink / raw)
To: pbonzini, richard.henderson, tony.nguyen
Cc: Zenghui Yu, wanghaibin.wang, qemu-devel, Euler Robot
Our robot reported the following compile-time warning while compiling
Qemu with -fno-inline cflags:
In function 'load_memop',
inlined from 'load_helper' at /qemu/accel/tcg/cputlb.c:1578:20,
inlined from 'full_ldub_mmu' at /qemu/accel/tcg/cputlb.c:1624:12:
/qemu/accel/tcg/cputlb.c:1502:9: error: call to 'qemu_build_not_reached' declared with attribute error: code path is reachable
qemu_build_not_reached();
^~~~~~~~~~~~~~~~~~~~~~~~
[...]
It looks like a false-positive because only (MO_UB ^ MO_BSWAP) will
hit the default case in load_memop() while need_swap (size > 1) has
already ensured that MO_UB is not involved.
So the thing is that compilers get confused by the -fno-inline and
just can't accurately evaluate memop_size(op) at compile time, and
then the qemu_build_not_reached() is wrongly triggered by (MO_UB ^
MO_BSWAP). Let's carefully don't use the compile-time assert when
no functions will be inlined into their callers.
Reported-by: Euler Robot <euler.robot@huawei.com>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
v2 is actually written by Richard Henderson.
v1: https://lore.kernel.org/r/20200205081703.631-1-yuzenghui@huawei.com
include/qemu/compiler.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 85c02c16d3..c76281f354 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -236,7 +236,7 @@
* supports QEMU_ERROR, this will be reported at compile time; otherwise
* this will be reported at link time due to the missing symbol.
*/
-#ifdef __OPTIMIZE__
+#if defined(__OPTIMIZE__) && !defined(__NO_INLINE__)
extern void QEMU_NORETURN QEMU_ERROR("code path is reachable")
qemu_build_not_reached(void);
#else
--
2.19.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] compiler.h: Don't use compile-time assert when __NO_INLINE__ is defined
2020-02-05 14:15 [PATCH v2] compiler.h: Don't use compile-time assert when __NO_INLINE__ is defined Zenghui Yu
@ 2020-02-16 3:21 ` Richard Henderson
0 siblings, 0 replies; 2+ messages in thread
From: Richard Henderson @ 2020-02-16 3:21 UTC (permalink / raw)
To: Zenghui Yu, pbonzini, tony.nguyen
Cc: wanghaibin.wang, qemu-devel, Euler Robot
On 2/5/20 6:15 AM, Zenghui Yu wrote:
> Our robot reported the following compile-time warning while compiling
> Qemu with -fno-inline cflags:
>
> In function 'load_memop',
> inlined from 'load_helper' at /qemu/accel/tcg/cputlb.c:1578:20,
> inlined from 'full_ldub_mmu' at /qemu/accel/tcg/cputlb.c:1624:12:
> /qemu/accel/tcg/cputlb.c:1502:9: error: call to 'qemu_build_not_reached' declared with attribute error: code path is reachable
> qemu_build_not_reached();
> ^~~~~~~~~~~~~~~~~~~~~~~~
> [...]
>
> It looks like a false-positive because only (MO_UB ^ MO_BSWAP) will
> hit the default case in load_memop() while need_swap (size > 1) has
> already ensured that MO_UB is not involved.
>
> So the thing is that compilers get confused by the -fno-inline and
> just can't accurately evaluate memop_size(op) at compile time, and
> then the qemu_build_not_reached() is wrongly triggered by (MO_UB ^
> MO_BSWAP). Let's carefully don't use the compile-time assert when
> no functions will be inlined into their callers.
>
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Suggested-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
>
> v2 is actually written by Richard Henderson.
>
> v1: https://lore.kernel.org/r/20200205081703.631-1-yuzenghui@huawei.com
>
> include/qemu/compiler.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Queued to tcg-next.
r~
^ permalink raw reply [flat|nested] 2+ messages in thread
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