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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