Subject: [PATCH -tip tracing/kprobes] PPC: Powerpc port of the kprobe-based event tracer

From: Mahesh Salgaonkar <[email-masked]>
Date: Wed, 16 Dec 2009 10:09:33 +0530

This patch ports the kprobe-based event tracer to powerpc. This patch
is based in x86 port. This brings powerpc on par with x86.

Port the following API's to ppc for accessing registers and stack entries
from pt_regs.

- regs_query_register_offset(const char *name)
   Query the offset of "name" register.

- regs_query_register_name(unsigned int offset)
   Query the name of register by its offset.

- regs_get_register(struct pt_regs *regs, unsigned int offset)
   Get the value of a register by its offset.

- regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
   Check the address is in the kernel stack.

- regs_get_kernel_stack_nth(struct pt_regs *reg, unsigned int nth)
   Get Nth entry of the kernel stack. (N >= 0)

- regs_get_argument_nth(struct pt_regs *reg, unsigned int nth)
   Get Nth argument at function call. (N >= 0)

Signed-off-by: Mahesh Salgaonkar <[email-masked]>
Acked-by: Masami Hiramatsu <[email-masked]>
---
 arch/powerpc/include/asm/ptrace.h |   64 +++++++++++++++++
 arch/powerpc/kernel/ptrace.c      |  141 ++++++++++++++++++++++++++++++++++++++
 kernel/trace/Kconfig              |    2 
 3 files changed, 206 insertions(+), 1 deletion(-)

Index: linux-2.6-tip/arch/powerpc/include/asm/ptrace.h
===================================================================
--- linux-2.6-tip.orig/arch/powerpc/include/asm/ptrace.h
+++ linux-2.6-tip/arch/powerpc/include/asm/ptrace.h
@@ -83,6 +83,7 @@ struct pt_regs {
 
 #define instruction_pointer(regs) ((regs)->nip)
 #define user_stack_pointer(regs) ((regs)->gpr[1])
+#define kernel_stack_pointer(regs) ((regs)->gpr[1])
 #define regs_return_value(regs) ((regs)->gpr[3])
 
 #ifdef CONFIG_SMP
@@ -131,6 +132,69 @@ do {									      \
 } while (0)
 #endif /* __powerpc64__ */
 
+/* Query offset/name of register from its name/offset */
+#include <linux/stddef.h>
+#include <linux/thread_info.h>
+extern int regs_query_register_offset(const char *name);
+extern const char *regs_query_register_name(unsigned int offset);
+/* Get Nth argument at function call */
+extern unsigned long regs_get_argument_nth(struct pt_regs *regs,
+						unsigned int n);
+#define MAX_REG_OFFSET (offsetof(struct pt_regs, result))
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:	   pt_regs from which register value is gotten
+ * @offset:    offset number of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs,
+						unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+	return *(unsigned long *)((unsigned long)regs + offset);
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:      pt_regs which contains kernel stack pointer.
+ * @addr:      address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+
+static inline bool regs_within_kernel_stack(struct pt_regs *regs,
+						unsigned long addr)
+{
+	return ((addr & ~(THREAD_SIZE - 1))  ==
+		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:	pt_regs which contains kernel stack pointer.
+ * @n:		stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+						      unsigned int n)
+{
+	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+	addr += n;
+	if (regs_within_kernel_stack(regs, (unsigned long)addr))
+		return *addr;
+	else
+		return 0;
+}
+
 /*
  * These are defined as per linux/ptrace.h, which see.
  */
Index: linux-2.6-tip/arch/powerpc/kernel/ptrace.c
===================================================================
--- linux-2.6-tip.orig/arch/powerpc/kernel/ptrace.c
+++ linux-2.6-tip/arch/powerpc/kernel/ptrace.c
@@ -39,6 +39,147 @@
 #include <asm/system.h>
 
 /*
+ * The parameter save area on the stack is used to store arguments being passed
+ * to callee function and is located at fixed offset from stack pointer.
+ */
+#ifdef CONFIG_PPC32
+#define PARAMETER_SAVE_AREA_OFFSET	24  /* bytes */
+#else /* CONFIG_PPC32 */
+#define PARAMETER_SAVE_AREA_OFFSET	48  /* bytes */
+#endif
+
+struct pt_regs_offset {
+	const char *name;
+	int offset;
+};
+
+#define REG_OFFSET_NAME(r) {.name = #r, .offset = offsetof(struct pt_regs, r)}
+#define REG_OFFSET_END {.name = NULL, .offset = 0}
+
+static const struct pt_regs_offset regoffset_table[] = {
+	REG_OFFSET_NAME(gpr[0]),
+	REG_OFFSET_NAME(gpr[1]),
+	REG_OFFSET_NAME(gpr[2]),
+	REG_OFFSET_NAME(gpr[3]),
+	REG_OFFSET_NAME(gpr[4]),
+	REG_OFFSET_NAME(gpr[5]),
+	REG_OFFSET_NAME(gpr[6]),
+	REG_OFFSET_NAME(gpr[7]),
+	REG_OFFSET_NAME(gpr[8]),
+	REG_OFFSET_NAME(gpr[9]),
+	REG_OFFSET_NAME(gpr[10]),
+	REG_OFFSET_NAME(gpr[11]),
+	REG_OFFSET_NAME(gpr[12]),
+	REG_OFFSET_NAME(gpr[13]),
+	REG_OFFSET_NAME(gpr[14]),
+	REG_OFFSET_NAME(gpr[15]),
+	REG_OFFSET_NAME(gpr[16]),
+	REG_OFFSET_NAME(gpr[17]),
+	REG_OFFSET_NAME(gpr[18]),
+	REG_OFFSET_NAME(gpr[19]),
+	REG_OFFSET_NAME(gpr[20]),
+	REG_OFFSET_NAME(gpr[21]),
+	REG_OFFSET_NAME(gpr[22]),
+	REG_OFFSET_NAME(gpr[23]),
+	REG_OFFSET_NAME(gpr[24]),
+	REG_OFFSET_NAME(gpr[25]),
+	REG_OFFSET_NAME(gpr[26]),
+	REG_OFFSET_NAME(gpr[27]),
+	REG_OFFSET_NAME(gpr[28]),
+	REG_OFFSET_NAME(gpr[29]),
+	REG_OFFSET_NAME(gpr[30]),
+	REG_OFFSET_NAME(gpr[31]),
+	REG_OFFSET_NAME(nip),
+	REG_OFFSET_NAME(msr),
+	REG_OFFSET_NAME(orig_gpr3),
+	REG_OFFSET_NAME(ctr),
+	REG_OFFSET_NAME(link),
+	REG_OFFSET_NAME(xer),
+	REG_OFFSET_NAME(ccr),
+#ifdef CONFIG_PPC64
+	REG_OFFSET_NAME(softe),
+#else
+	REG_OFFSET_NAME(mq),
+#endif
+	REG_OFFSET_NAME(trap),
+	REG_OFFSET_NAME(dar),
+	REG_OFFSET_NAME(dsisr),
+	REG_OFFSET_NAME(result),
+	REG_OFFSET_END,
+};
+
+/**
+ * regs_query_register_offset() - query register offset from its name
+ * @name:	the name of a register
+ *
+ * regs_query_register_offset() returns the offset of a register in struct
+ * pt_regs from its name. If the name is invalid, this returns -EINVAL;
+ */
+int regs_query_register_offset(const char *name)
+{
+	const struct pt_regs_offset *roff;
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (!strcmp(roff->name, name))
+			return roff->offset;
+	return -EINVAL;
+}
+
+/**
+ * regs_query_register_name() - query register name from its offset
+ * @offset:	the offset of a register in struct pt_regs.
+ *
+ * regs_query_register_name() returns the name of a register from its
+ * offset in struct pt_regs. If the @offset is invalid, this returns NULL;
+ */
+const char *regs_query_register_name(unsigned int offset)
+{
+	const struct pt_regs_offset *roff;
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (roff->offset == offset)
+			return roff->name;
+	return NULL;
+}
+
+static const int arg_offs_table[] = {
+	[0] = offsetof(struct pt_regs, gpr[3]),
+	[1] = offsetof(struct pt_regs, gpr[4]),
+	[2] = offsetof(struct pt_regs, gpr[5]),
+	[3] = offsetof(struct pt_regs, gpr[6]),
+	[4] = offsetof(struct pt_regs, gpr[7]),
+	[5] = offsetof(struct pt_regs, gpr[8]),
+	[6] = offsetof(struct pt_regs, gpr[9]),
+	[7] = offsetof(struct pt_regs, gpr[10])
+};
+
+/**
+ * regs_get_argument_nth() - get Nth argument at function call
+ * @regs:	pt_regs which contains registers at function entry.
+ * @n:		argument number.
+ *
+ * regs_get_argument_nth() returns @n th argument of a function call.
+ * Since usually the kernel stack will be changed right after function entry,
+ * you must use this at function entry. If the @n th entry is NOT in the
+ * kernel stack or pt_regs, this returns 0.
+ */
+unsigned long regs_get_argument_nth(struct pt_regs *regs, unsigned int n)
+{
+	if (n < ARRAY_SIZE(arg_offs_table))
+		return *(unsigned long *)((char *)regs + arg_offs_table[n]);
+	else {
+		/*
+		 * If more arguments are passed that can be stored in
+		 * registers, the remaining arguments are stored in the
+		 * parameter save area located at fixed offset from stack
+		 * pointer.
+		 * Following the PowerPC ABI, the first few arguments are
+		 * actually passed in registers (r3-r10), with equivalent space
+		 * left unused in the parameter save area.
+		 */
+		n += (PARAMETER_SAVE_AREA_OFFSET / sizeof(unsigned long));
+		return regs_get_kernel_stack_nth(regs, n);
+	}
+}
+/*
  * does not yet catch signals sent when the child dies.
  * in exit.c or in signal.c.
  */
Index: linux-2.6-tip/kernel/trace/Kconfig
===================================================================
--- linux-2.6-tip.orig/kernel/trace/Kconfig
+++ linux-2.6-tip/kernel/trace/Kconfig
@@ -464,7 +464,7 @@ config BLK_DEV_IO_TRACE
 
 config KPROBE_EVENT
 	depends on KPROBES
-	depends on X86
+	depends on X86 || PPC
 	bool "Enable kprobes-based dynamic events"
 	select TRACING
 	default y