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Date: Fri, 26 Jun 2020 04:42:46 +0200 From: Heinrich Schuchardt <xypron.glpk@....de> To: Atish Patra <atish.patra@....com>, linux-kernel@...r.kernel.org Cc: Ard Biesheuvel <ardb@...nel.org>, linux-efi@...r.kernel.org, linux-riscv@...ts.infradead.org, Masahiro Yamada <masahiroy@...nel.org>, Palmer Dabbelt <palmer@...belt.com>, linux-arm-kernel@...ts.infradead.org Subject: Re: [RFC PATCH 01/11] efi: Fix gcc error around __umoddi3 for 32 bit builds 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@....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); >
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