Messages in this thread | | | Date | Tue, 12 Nov 2013 14:17:27 +0000 | From | Ben Dooks <> | Subject | Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions |
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On 12/11/13 14:04, Russell King - ARM Linux wrote: > On Tue, Nov 12, 2013 at 09:01:16AM -0500, Nicolas Pitre wrote: >> What about this patch which I think is currently your best option. Note >> it would need to use the facilities from asm/opcodes.h to make it endian >> agnostic. >> >> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c >> index 6a1b8a81b1..379cffe4ab 100644 >> --- a/arch/arm/kernel/setup.c >> +++ b/arch/arm/kernel/setup.c >> @@ -383,6 +383,34 @@ static void __init cpuid_init_hwcaps(void) >> elf_hwcap |= HWCAP_IDIVT; >> } >> >> + /* >> + * Patch our division routines with the corresponding opcode >> + * if the hardware supports it. >> + */ >> + if (IS_ENABLED(CONFIG_THUMB2_KERNEL) && (elf_hwcap & HWCAP_IDIVT)) { >> + extern char __aeabi_uidiv, __aeabi_idiv; >> + u16 *uidiv = (u16 *)&__aeabi_uidiv; >> + u16 *idiv = (u16 *)&__aeabi_idiv; >> + >> + uidiv[0] = 0xfbb0; /* udiv r0, r0, r1 */ >> + uidiv[1] = 0xf0f1; >> + uidiv[2] = 0x4770; /* bx lr */ >> + >> + idiv[0] = 0xfb90; /* sdiv r0, r0, r1 */ >> + idiv[1] = 0xf0f1; >> + idiv[2] = 0x4770; /* bx lr */ >> + } else if (!IS_ENABLED(CONFIG_THUMB2_KERNEL) && (elf_hwcap & HWCAP_IDIVA)) { >> + extern char __aeabi_uidiv, __aeabi_idiv; >> + u32 *uidiv = (u32 *)&__aeabi_uidiv; >> + u32 *idiv = (u32 *)&__aeabi_idiv; >> + >> + uidiv[0] = 0xe730f110; /* udiv r0, r0, r1 */ >> + uidiv[1] = 0xe12fff1e; /* bx lr */ >> + >> + idiv[0] = 0xe710f110; /* sdiv r0, r0, r1 */ >> + idiv[1] = 0xe12fff1e; /* bx lr */ >> + } > > What about endianness, and what if XIP is enabled?
I was also going to add a note about endian-ness.
Given these are single instructoins for ARM, is it possible we could make a table of all the callers and fix them up when we initialise as we do for the SMP/UP case and for page-offset?
-- Ben Dooks http://www.codethink.co.uk/ Senior Engineer Codethink - Providing Genius
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