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From: Heinrich Schuchardt <xypron.glpk@gmx.de>
To: Atish Patra <atish.patra@wdc.com>, linux-kernel@vger.kernel.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	linux-efi@vger.kernel.org, linux-riscv@lists.infradead.org,
	Masahiro Yamada <masahiroy@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH 01/11] efi: Fix gcc error around __umoddi3 for 32 bit builds
Date: Fri, 26 Jun 2020 04:42:46 +0200	[thread overview]
Message-ID: <5e2ce2ae-5458-8579-576a-76721f7d3b08@gmx.de> (raw)
In-Reply-To: <20200625234516.31406-2-atish.patra@wdc.com>

On 6/26/20 1:45 AM, Atish Patra wrote:
> 32bit gcc doesn't support modulo operation on 64 bit data. It results in
> a __umoddi3 error while building EFI for 32 bit.
>
> Use bitwise operations instead of modulo operations to fix the issue.
>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
>  drivers/firmware/efi/libstub/alignedmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/libstub/alignedmem.c b/drivers/firmware/efi/libstub/alignedmem.c
> index cc89c4d6196f..1de9878ddd3a 100644
> --- a/drivers/firmware/efi/libstub/alignedmem.c
> +++ b/drivers/firmware/efi/libstub/alignedmem.c
> @@ -44,7 +44,7 @@ efi_status_t efi_allocate_pages_aligned(unsigned long size, unsigned long *addr,
>  	*addr = ALIGN((unsigned long)alloc_addr, align);
>
>  	if (slack > 0) {
> -		int l = (alloc_addr % align) / EFI_PAGE_SIZE;
> +		int l = (alloc_addr & (align - 1)) / EFI_PAGE_SIZE;

Here you rely on the compiler to silently convert the division by
EFI_PAGE_SIZE into a right shift. Wouldn't it be cleaner to use
EFI_PAGE_SHIFT to explicitly avoid a dependency on __udivdi3()?

slack = (align >> EFI_PAGE_SHIFT) - 1;
...
int l = (alloc_addr & (align - 1)) >> EFI_PAGE_SHIFT;

Best regards

Heinrich

>
>  		if (l) {
>  			efi_bs_call(free_pages, alloc_addr, slack - l + 1);
>


  reply	other threads:[~2020-06-26  2:43 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-25 23:45 [RFC PATCH 00/11] Add UEFI support for RISC-V Atish Patra
2020-06-25 23:45 ` [RFC PATCH 01/11] efi: Fix gcc error around __umoddi3 for 32 bit builds Atish Patra
2020-06-26  2:42   ` Heinrich Schuchardt [this message]
2020-06-26 21:56     ` Atish Patra
2020-06-26 22:03       ` Ard Biesheuvel
2020-06-27  9:22         ` Ard Biesheuvel
2020-06-29 20:09           ` Atish Patra
2020-07-22 22:48   ` [tip: efi/urgent] efi/libstub: " tip-bot2 for Atish Patra
2020-06-25 23:45 ` [RFC PATCH 02/11] RISC-V: Move DT mapping outof fixmap Atish Patra
2020-06-25 23:45 ` [RFC PATCH 03/11] RISC-V: Setup exception vector early Atish Patra
2020-06-25 23:45 ` [RFC PATCH 04/11] RISC-V: Add early ioremap support Atish Patra
2020-06-25 23:45 ` [RFC PATCH 05/11] RISC-V: Set maximum number of mapped pages correctly Atish Patra
2020-06-25 23:45 ` [RFC PATCH 06/11] riscv: Parse all memory blocks to remove unusable memory Atish Patra
2020-06-25 23:45 ` [RFC PATCH 07/11] include: pe.h: Add RISC-V related PE definition Atish Patra
2020-06-25 23:45 ` [RFC PATCH 08/11] RISC-V: Add PE/COFF header for EFI stub Atish Patra
2020-06-25 23:45 ` [RFC PATCH 09/11] RISC-V: Add EFI stub support Atish Patra
2020-06-25 23:45 ` [RFC PATCH 10/11] efi: Rename arm-init to efi-init common for all arch Atish Patra
2020-06-26  3:00   ` Heinrich Schuchardt
2020-06-26 21:57     ` Atish Patra
2020-06-25 23:45 ` [RFC PATCH 11/11] RISC-V: Add EFI runtime services Atish Patra

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