Re: [kvm-unit-tests PATCH v2 2/2] s390x: Fix gcc 12 warning about array bounds

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Fri, 20 May 2022 16:05:46 +0200
Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:

> gcc 12 warns about pointer constant <4k dereference.
> Silence the warning by using the extern lowcore symbol to derive the
> pointers. This way gcc cannot conclude that the pointer is <4k.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
> ---
>  lib/s390x/asm/mem.h | 4 ++++
>  s390x/emulator.c    | 5 +++--
>  s390x/skey.c        | 2 +-
>  3 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/s390x/asm/mem.h b/lib/s390x/asm/mem.h
> index 845c00cc..e7901fe0 100644
> --- a/lib/s390x/asm/mem.h
> +++ b/lib/s390x/asm/mem.h
> @@ -7,6 +7,10 @@
>   */
>  #ifndef _ASMS390X_MEM_H_
>  #define _ASMS390X_MEM_H_
> +#include <asm/arch_def.h>
> +
> +/* pointer to 0 used to avoid compiler warnings */
> +uint8_t *mem_all = (uint8_t *)&lowcore;

this is defined in a .h, so maybe it's better to declare it static?


although maybe you can simply declare a macro like this:

#define MEM(x) ((void *)((uint8_t *)&lowcore + (x)))

and then just use MEM(x)...

(please find a less generic name for MEM, though)

>  
>  #define SKEY_ACC	0xf0
>  #define SKEY_FP		0x08
> diff --git a/s390x/emulator.c b/s390x/emulator.c
> index c9182ea4..afc3c213 100644
> --- a/s390x/emulator.c
> +++ b/s390x/emulator.c
> @@ -12,6 +12,7 @@
>  #include <asm/cpacf.h>
>  #include <asm/interrupt.h>
>  #include <asm/float.h>
> +#include <asm/mem.h>
>  #include <linux/compiler.h>
>  
>  static inline void __test_spm_ipm(uint8_t cc, uint8_t key)
> @@ -138,7 +139,7 @@ static __always_inline void __test_cpacf_invalid_parm(unsigned int opcode)
>  {
>  	report_prefix_push("invalid parm address");
>  	expect_pgm_int();
> -	__cpacf_query(opcode, (void *) -1);
> +	__cpacf_query(opcode, (cpacf_mask_t *)&mem_all[-1]);

...for example here MEM(-1)

>  	check_pgm_int_code(PGM_INT_CODE_ADDRESSING);
>  	report_prefix_pop();
>  }
> @@ -148,7 +149,7 @@ static __always_inline void __test_cpacf_protected_parm(unsigned int opcode)
>  	report_prefix_push("protected parm address");
>  	expect_pgm_int();
>  	low_prot_enable();
> -	__cpacf_query(opcode, (void *) 8);
> +	__cpacf_query(opcode, (cpacf_mask_t *)&mem_all[8]);

... MEM(8)

>  	low_prot_disable();
>  	check_pgm_int_code(PGM_INT_CODE_PROTECTION);
>  	report_prefix_pop();
> diff --git a/s390x/skey.c b/s390x/skey.c
> index 32bf1070..42bf598c 100644
> --- a/s390x/skey.c
> +++ b/s390x/skey.c
> @@ -349,7 +349,7 @@ static void test_set_prefix(void)
>  	set_storage_key(pagebuf, 0x28, 0);
>  	expect_pgm_int();
>  	install_page(root, virt_to_pte_phys(root, pagebuf), 0);
> -	set_prefix_key_1((uint32_t *)2048);
> +	set_prefix_key_1((uint32_t *)&mem_all[2048]);

... MEM(2048)

>  	install_page(root, 0, 0);
>  	check_pgm_int_code(PGM_INT_CODE_PROTECTION);
>  	report(get_prefix() == old_prefix, "did not set prefix");