[PATCH]: Sparc64 immediate values

[David Miller]

As described in the commit log I think that two instruction sequences
can be done properly, and we'd need that to support 16-bit and 32-bit
values on sparc64 since the available instructions are "load high
22-bits" and "or in signed low 13 bits".

One idea is to capture all cpus other than the immediate value
updating cpu.

These other cpus look to see if their program counter falls
on an immediate value instruction sequence.  Much like how we
lookup exceptions we can sort the table and use binary search
so that it isn't too slow.

If they find themselves in such a sequence, they examine the
destination register in the last instruction, load that register with
the proper immediate value, and advance the program counter.  Then
they wait to be released.

The updater does the instruction update unimpeded, flushes the
instruction cache or whatever needs to be done, and then releases the
other cpus.

PowerPC could use this scheme too, if it does in fact work.

Please add to the ftrace tree, thanks.

commit f2b14974b823a9cd9b6f5c0d423945caa15de8a2
Author: David S. Miller <davem@xxxxxxxxxxxxx>
Date:   Tue May 13 04:29:30 2008 -0700

    sparc64: Optimized immediate value implementation.
    
    We can only do byte sized values currently.
    
    In order to support even 16-bit immediates we would need a 2
    instruction sequence.
    
    I believe that can be made to work with a suitable breakpoint or some
    other kind of special patching sequence, but that isn't attempted
    here.
    
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>

diff --git a/arch/sparc64/Kconfig b/arch/sparc64/Kconfig
index eb36f3b..4c40862 100644
--- a/arch/sparc64/Kconfig
+++ b/arch/sparc64/Kconfig
@@ -14,6 +14,7 @@ config SPARC64
 	select HAVE_IDE
 	select HAVE_LMB
 	select HAVE_ARCH_KGDB
+	select HAVE_IMMEDIATE
 
 config GENERIC_TIME
 	bool
diff --git a/arch/sparc64/kernel/Makefile b/arch/sparc64/kernel/Makefile
index ec4f5eb..311c797 100644
--- a/arch/sparc64/kernel/Makefile
+++ b/arch/sparc64/kernel/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_MODULES) += module.o
 obj-$(CONFIG_US3_FREQ) += us3_cpufreq.o
 obj-$(CONFIG_US2E_FREQ) += us2e_cpufreq.o
 obj-$(CONFIG_KPROBES) += kprobes.o
+obj-$(CONFIG_IMMEDIATE) += immediate.o
 obj-$(CONFIG_SUN_LDOMS) += ldc.o vio.o viohs.o ds.o
 obj-$(CONFIG_AUDIT) += audit.o
 obj-$(CONFIG_AUDIT)$(CONFIG_COMPAT) += compat_audit.o
diff --git a/arch/sparc64/kernel/immediate.c b/arch/sparc64/kernel/immediate.c
new file mode 100644
index 0000000..be76f28
--- /dev/null
+++ b/arch/sparc64/kernel/immediate.c
@@ -0,0 +1,48 @@
+#include <linux/module.h>
+#include <linux/immediate.h>
+#include <linux/string.h>
+#include <linux/kprobes.h>
+
+#include <asm/system.h>
+
+int arch_imv_update(const struct __imv *imv, int early)
+{
+	unsigned long imv_vaddr = imv->imv;
+	unsigned long var_vaddr = imv->var;
+	u32 insn, *ip = (u32 *) imv_vaddr;
+
+	insn = *ip;
+
+#ifdef CONFIG_KPROBES
+	switch (imv->size) {
+	case 1:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (unlikely(!early &&
+		     (insn == BREAKPOINT_INSTRUCTION ||
+		      insn == BREAKPOINT_INSTRUCTION_2))) {
+		printk(KERN_WARNING "Immediate value in conflict with kprobe. "
+				    "Variable at %p, "
+				    "instruction at %p, size %u\n",
+				    ip, (void *)var_vaddr, imv->size);
+		return -EBUSY;
+	}
+#endif
+
+	switch (imv->size) {
+	case 1:
+		if ((insn & 0x1fff) == *(uint8_t *)var_vaddr)
+			return 0;
+		insn &= ~0x00001fff;
+		insn |= (u32) (*(uint8_t *)var_vaddr);
+		break;
+	default:
+		return -EINVAL;
+	}
+	*ip = insn;
+	flushi(ip);
+	return 0;
+}
diff --git a/include/asm-sparc64/immediate.h b/include/asm-sparc64/immediate.h
new file mode 100644
index 0000000..3673afd
--- /dev/null
+++ b/include/asm-sparc64/immediate.h
@@ -0,0 +1,37 @@
+#ifndef _ASM_SPARC64_IMMEDIATE_H
+#define _ASM_SPARC64_IMMEDIATE_H
+
+struct __imv {
+	unsigned int var;
+	unsigned int imv;
+	unsigned char size;
+} __attribute__ ((packed));
+
+#define imv_read(name)							\
+	({								\
+		__typeof__(name##__imv) value;				\
+		BUILD_BUG_ON(sizeof(value) > 8);			\
+		switch (sizeof(value)) {				\
+		case 1:							\
+			asm(".section __imv,\"aw\",@progbits\n\t"	\
+					".uaword %c1, 1f\n\t"		\
+					".byte 1\n\t"			\
+					".previous\n\t"			\
+					"1: mov 0, %0\n\t"		\
+				: "=r" (value)				\
+				: "i" (&name##__imv));			\
+			break;						\
+		case 2:							\
+		case 4:							\
+		case 8:	value = name##__imv;				\
+			break;						\
+		};							\
+		value;							\
+	})
+
+#define imv_cond(name)	imv_read(name)
+#define imv_cond_end()
+
+extern int arch_imv_update(const struct __imv *imv, int early);
+
+#endif /* _ASM_SPARC64_IMMEDIATE_H */
diff --git a/kernel/immediate.c b/kernel/immediate.c
index 3668a7f..1b4c5cf 100644
--- a/kernel/immediate.c
+++ b/kernel/immediate.c
@@ -62,8 +62,8 @@ void imv_update_range(struct __imv *begin,
 				"Invalid immediate value. "
 				"Variable at %p, "
 				"instruction at %p, size %hu\n",
-				(void *)iter->imv,
-				(void *)iter->var, iter->size);
+			        (void *)(long)iter->imv,
+			        (void *)(long)iter->var, iter->size);
 skip:
 		mutex_unlock(&imv_mutex);
 	}
--
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