| Message ID | 20200205081703.631-1-yuzenghui@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | memory: Use QEMU_ALWAYS_INLINE to silence compile-time warning | expand |
On 2/5/20 8:17 AM, Zenghui Yu wrote: > Our robot reported the following compile-time warning while compiling > Qemu with -fno-inline cflags: Why are you doing this? > > 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(); > ^~~~~~~~~~~~~~~~~~~~~~~~ > [...] Of course, the assert is compiled out when optimization is off, which is the only time we expect inlining to be off. The patch isn't wrong, exactly, but I question whether we want to support completely arbitrary combinations of compile flags. r~
On 2/5/20 10:01 AM, Richard Henderson wrote: > On 2/5/20 8:17 AM, Zenghui Yu wrote: >> Our robot reported the following compile-time warning while compiling >> Qemu with -fno-inline cflags: > > Why are you doing this? > >> >> 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(); >> ^~~~~~~~~~~~~~~~~~~~~~~~ >> [...] > > Of course, the assert is compiled out when optimization is off, which is the > only time we expect inlining to be off. > > The patch isn't wrong, exactly, but I question whether we want to support > completely arbitrary combinations of compile flags. To follow up: if you *really* need to support -fno-inline, then perhaps the correct patch is to change - #ifdef __OPTIMIZE__ + #if defined(__OPTIMIZE__) && !defined(__NO_INLINE__) extern void QEMU_NORETURN QEMU_ERROR("code path is reachable") qemu_build_not_reached(void); #else #define qemu_build_not_reached() g_assert_not_reached() #endif within include/qemu/compiler.h. r~
Hi Richard, On 2020/2/5 18:31, Richard Henderson wrote: > On 2/5/20 10:01 AM, Richard Henderson wrote: >> On 2/5/20 8:17 AM, Zenghui Yu wrote: >>> Our robot reported the following compile-time warning while compiling >>> Qemu with -fno-inline cflags: >> >> Why are you doing this? I'm not sure why it was added in the building test. As you said, there's just a arbitrary combination of compile flags. >> >>> >>> 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(); >>> ^~~~~~~~~~~~~~~~~~~~~~~~ >>> [...] >> >> Of course, the assert is compiled out when optimization is off, which is the >> only time we expect inlining to be off. >> >> The patch isn't wrong, exactly, but I question whether we want to support >> completely arbitrary combinations of compile flags. It doesn't hurt to do the right thing, and you already have the good approach :) > > To follow up: if you *really* need to support -fno-inline, then perhaps the > correct patch is to change > > - #ifdef __OPTIMIZE__ > + #if defined(__OPTIMIZE__) && !defined(__NO_INLINE__) > extern void QEMU_NORETURN QEMU_ERROR("code path is reachable") > qemu_build_not_reached(void); > #else > #define qemu_build_not_reached() g_assert_not_reached() > #endif > > within include/qemu/compiler.h. Thanks for this. I've tested it with -fno-inlie and it indeed works. I will send it as v2. Thanks, Zenghui
diff --git a/include/exec/memop.h b/include/exec/memop.h index 529d07b02d..5403f960e0 100644 --- a/include/exec/memop.h +++ b/include/exec/memop.h @@ -110,7 +110,7 @@ typedef enum MemOp { } MemOp; /* MemOp to size in bytes. */ -static inline unsigned memop_size(MemOp op) +static inline unsigned QEMU_ALWAYS_INLINE memop_size(MemOp op) { return 1 << (op & MO_SIZE); }
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. Apply QEMU_ALWAYS_INLINE on memop_size() to make sure it will always be inlined while we're using the compile-time assert, so that the compilers won't get confused. Reported-by: Euler Robot <euler.robot@huawei.com> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com> --- Not sure if it's the right fix, but seems works fine to me :) include/exec/memop.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)