> On 9 Jul 2021, at 09:16, Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>
> On Thu, Jul 8, 2021 at 8:02 PM Martin Sebor via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi Ian,
>>
>> Yesterday's enhancement to -Warray-bounds has exposed a couple of
>> issues in libgo where the code writes into an invalid constant
>> address that the warning is designed to flag.
>>
>> On the assumption that those invalid addresses are deliberate,
>> the attached patch suppresses these instances by using #pragma
>> GCC diagnostic but I don't think I'm supposed to commit it (at
>> least Git won't let me). To avoid Go bootstrap failures please
>> either apply the patch or otherwise suppress the warning (e.g.,
>> by using a volatile pointer temporary).
>
> Btw, I don't think we should diagnose things like
>
> *(int*)0x21 = 0x21;
>
> when somebody literally writes that he'll be just annoyed by diagnostics.
And we have an assortment of similar cases in 32-bit ARM kernel-page helpers.
At the moment building libatomic for arm-linux-gnueabihf fails with:
===
In function ‘select_test_and_set_8’,
inlined from ‘select_test_and_set_8’ at
/home/tcwg-buildslave/workspace/tcwg-dev-build/snapshots/gcc.git~master/libatomic/tas_n.c:115:1:
/home/tcwg-buildslave/workspace/tcwg-dev-build/snapshots/gcc.git~master/libatomic/config/linux/arm/host-config.h:42:34:
error: array subscript 0 is outside array bounds of ‘unsigned int[0]’
[-Werror=array-bounds]
42 | #define __kernel_helper_version (*(unsigned int *)0xffff0ffc)
| ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
===
In libatomic/config/linux/arm/host-config.h we have:
===
/* Kernel helper for 32-bit compare-and-exchange. */
typedef int (__kernel_cmpxchg_t) (UWORD oldval, UWORD newval, UWORD *ptr);
#define __kernel_cmpxchg (*(__kernel_cmpxchg_t *) 0xffff0fc0)
/* Kernel helper for 64-bit compare-and-exchange. */
typedef int (__kernel_cmpxchg64_t) (const U_8 * oldval, const U_8 * newval,
U_8 *ptr);
#define __kernel_cmpxchg64 (*(__kernel_cmpxchg64_t *) 0xffff0f60)
/* Kernel helper for memory barrier. */
typedef void (__kernel_dmb_t) (void);
#define __kernel_dmb (*(__kernel_dmb_t *) 0xffff0fa0)
/* Kernel helper page version number. */
#define __kernel_helper_version (*(unsigned int *)0xffff0ffc)
===
--
Maxim Kuvyrkov
https://www.linaro.org
