linux-kernel - Re: [PATCH 2/2] selftests/mm: Fix a build failure on powerpc

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Message-ID: <f23608eb-3f4e-453c-bcfc-032f963d310c@linux.ibm.com>
Date: Mon, 28 Apr 2025 22:43:38 +0530
From: Donet Tom <donettom@...ux.ibm.com>
To: "Nysal Jan K.A." <nysal@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>
Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        linuxppc-dev@...ts.ozlabs.org, Kevin Brodsky <kevin.brodsky@....com>,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] selftests/mm: Fix a build failure on powerpc


On 4/28/25 6:49 PM, Nysal Jan K.A. wrote:
> The compiler is unaware of the size of code generated by the ".rept"
> assembler directive. This results in the compiler emitting branch
> instructions where the offset to branch to exceeds the maximum allowed
> value, resulting in build failures like the following:
>
>    CC       protection_keys
>    /tmp/ccypKWAE.s: Assembler messages:
>    /tmp/ccypKWAE.s:2073: Error: operand out of range (0x0000000000020158
>    is not between 0xffffffffffff8000 and 0x0000000000007ffc)
>    /tmp/ccypKWAE.s:2509: Error: operand out of range (0x0000000000020130
>    is not between 0xffffffffffff8000 and 0x0000000000007ffc)
>
> Fix the issue by manually adding nop instructions using the preprocessor.
>
> Fixes: 46036188ea1f5 ("selftests/mm: build with -O2")
> Reported-by: Madhavan Srinivasan <maddy@...ux.ibm.com>
> Signed-off-by: Nysal Jan K.A. <nysal@...ux.ibm.com>
> ---
>   tools/testing/selftests/mm/pkey-powerpc.h | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/mm/pkey-powerpc.h b/tools/testing/selftests/mm/pkey-powerpc.h
> index d8ec906b8120..17bf2d1b0192 100644
> --- a/tools/testing/selftests/mm/pkey-powerpc.h
> +++ b/tools/testing/selftests/mm/pkey-powerpc.h
> @@ -104,8 +104,18 @@ static inline void expect_fault_on_read_execonly_key(void *p1, int pkey)
>   	return;
>   }
>   
> +#define REPEAT_8(s) s s s s s s s s
> +#define REPEAT_64(s) REPEAT_8(s) REPEAT_8(s) REPEAT_8(s) REPEAT_8(s) \
> +		     REPEAT_8(s) REPEAT_8(s) REPEAT_8(s) REPEAT_8(s)
> +#define REPEAT_512(s) REPEAT_64(s) REPEAT_64(s) REPEAT_64(s) REPEAT_64(s) \
> +		      REPEAT_64(s) REPEAT_64(s) REPEAT_64(s) REPEAT_64(s)
> +#define REPEAT_4096(s) REPEAT_512(s) REPEAT_512(s) REPEAT_512(s) REPEAT_512(s) \
> +		       REPEAT_512(s) REPEAT_512(s) REPEAT_512(s) REPEAT_512(s)
> +#define REPEAT_16384(s) REPEAT_4096(s) REPEAT_4096(s) \
> +			REPEAT_4096(s) REPEAT_4096(s)
> +


Hi Nysal,

This change looks good to me. I tested in on power and the error is not seen.

   CC       droppable
   CC       guard-regions
   CC       soft-dirty
   CC       protection_keys
   CC       va_high_addr_switch
   CC       virtual_address_range
   CC       write_to_hugetlbfs

Reviewed-by:Donet Tom <donettom@...ux.ibm.com>
Tested-by: Donet Tom <donettom@...ux.ibm.com>


>   /* 4-byte instructions * 16384 = 64K page */
> -#define __page_o_noops() asm(".rept 16384 ; nop; .endr")
> +#define __page_o_noops() asm(REPEAT_16384("nop\n"))
>   
>   static inline void *malloc_pkey_with_mprotect_subpage(long size, int prot, u16 pkey)
>   {