Hi Mahesh !Hi Benjamin,
This function is used to validate whether the given address falls within the stack boundary. This gets invoked through kprobe pre/post handler routine's while fetching nth entry from the stack. Even though it is called in interrupt context, the pt_regs that we are using is in context of kernel routine where the probe was hit.+/**
+ * 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)));
+}
Out of curiosity, what is the above meant for ? I'm trying to understand
because it will not work with such things as interrupt or softirq
stack...
The purpose is to allow kernel developer to fetch/monitor n'th entry on the stack when the probe is hit, through ftrace plugin. It can also be used to fetch stack based arguments.+/**
+ * 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;
+}
Is this meant to fetch stack based arguments or do backtraces or similar
or does this have a different purpose ?
Yup, make sense. I will make the change. Will use gpr0...gpr31 to be consistent with pt_regs structure member name "gpr"./*
* These are defined as per linux/ptrace.h, which see.
*/
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index ef14988..e816aba 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -39,6 +39,108 @@
#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]),
I find it weird that you have the [ an ] in the name ... We usually name
these guys gpr0...gpr31 or even r0...r31. Is that name user visible ?
Maybe you should use a different macro GPR_OFFSET_NAME(num) that
generates both gpr[num] for the offsetof and r##num for the register
name.
I had included them to give an exact representation of pt_regs structure. However, I am ok with dropping them.+ 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,
+};
Do you need to expose orig_gpr3 and result there ?
Cheers,
Ben.