[PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions
From: Måns Rullgård <hidden>
Date: 2013-11-12 18:04:06
Also in:
lkml
Subsystem:
arm port, the rest · Maintainers:
Russell King, Linus Torvalds
Possibly related (same subject, not in this thread)
- 2013-11-12 · Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions · Nicolas Pitre <hidden>
- 2013-11-12 · Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions · Nicolas Pitre <hidden>
- 2013-11-12 · Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions · Måns Rullgård <hidden>
- 2013-11-12 · Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions · Nicolas Pitre <hidden>
- 2013-11-12 · Re: [PATCH v2] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions · Nicolas Pitre <hidden>
Nicolas Pitre [off-list ref] writes:
On Tue, 12 Nov 2013, M?ns Rullg?rd wrote:quoted
Nicolas Pitre [off-list ref] writes:quoted
On Tue, 12 Nov 2013, Ben Dooks wrote:quoted
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?Not really. Calls to those functions are generated by the compiler implicitly when a divisor operand is used and therefore we cannot annotate those calls. We'd have to use special accessors everywhere to replace the standard division operand (like we do for 64 by 32 bit divisions) but I doubt that people would accept that.It might be possible to extract this information from relocation tables.True, but only for individual .o files. Once the linker puts them together the information is lost, and trying to infer what the linker has done is insane. Filtering the compiler output to annotate idiv calls before it is assembled would probably be a better solution.
OK, here's an extremely ugly hootenanny of a patch. It seems to work on an A7 Cubieboard2. I would never suggest actually doing this, but maybe it can be useful for comparing performance against the more palatable solutions.
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 7397db6..cf1cd30 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile@@ -113,7 +113,7 @@ endif endif # Need -Uarm for gcc < 3.x -KBUILD_CFLAGS +=$(CFLAGS_ABI) $(CFLAGS_THUMB2) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm +KBUILD_CFLAGS +=$(CFLAGS_ABI) $(CFLAGS_THUMB2) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm -include asm/divhack.h KBUILD_AFLAGS +=$(CFLAGS_ABI) $(AFLAGS_THUMB2) $(arch-y) $(tune-y) -include asm/unified.h -msoft-float CHECKFLAGS += -D__arm__
diff --git a/arch/arm/include/asm/divhack.h b/arch/arm/include/asm/divhack.h
new file mode 100644
index 0000000..c750b78
--- /dev/null
+++ b/arch/arm/include/asm/divhack.h@@ -0,0 +1,23 @@ +__asm__ (".macro dobl tgt \n" + " .ifc \\tgt, __aeabi_idiv \n" + " .L.sdiv.\\@: \n" + " .pushsection .sdiv_tab.init, \"a\", %progbits \n" + " .word .L.sdiv.\\@ \n" + " .popsection \n" + " .endif \n" + " .ifc \\tgt, __aeabi_uidiv \n" + " .L.udiv.\\@: \n" + " .pushsection .udiv_tab.init, \"a\", %progbits \n" + " .word .L.udiv.\\@ \n" + " .popsection \n" + " .endif \n" + " bl \\tgt \n" + ".endm \n" + ".macro defbl \n" + " .macro bl tgt \n" + " .purgem bl \n" + " dobl \\tgt \n" + " defbl \n" + " .endm \n" + ".endm \n" + "defbl \n");
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 067815c1..b3a3fe1 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c@@ -375,6 +375,18 @@ static void __init cpuid_init_hwcaps(void) case 1: elf_hwcap |= HWCAP_IDIVT; } + + if (!IS_ENABLED(CONFIG_THUMB2_KERNEL) && (elf_hwcap & HWCAP_IDIVA)) { + extern u32 __sdiv_tab_start, __sdiv_tab_end; + extern u32 __udiv_tab_start, __udiv_tab_end; + u32 *div; + + for (div = &__sdiv_tab_start; div < &__sdiv_tab_end; div++) + *(u32 *)*div = 0xe710f110; + + for (div = &__udiv_tab_start; div < &__udiv_tab_end; div++) + *(u32 *)*div = 0xe730f110; + } } static void __init feat_v6_fixup(void)
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 43a31fb..3d5c103 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S@@ -176,6 +176,8 @@ SECTIONS CON_INITCALL SECURITY_INITCALL INIT_RAM_FS + __sdiv_tab_start = .; *(.sdiv_tab.init); __sdiv_tab_end = .; + __udiv_tab_start = .; *(.udiv_tab.init); __udiv_tab_end = .; } #ifndef CONFIG_XIP_KERNEL .exit.data : {
--
M?ns Rullg?rd
mans@mansr.com