[PATCH] Systemtap ppc64 runtime

[Hien Nguyen <hien at us dot ibm dot com>]

This patch implements the _stp_stack_print() function for the ppc64 
runtime. In order for this implementation to work, the kernel needs to 
be configured with CONFIG_KALLSYMS_ALL=y.

Some background. we use the kallsyms_lookup_name() to get access to some
of the unexported functions in the kernel. Under ppc64, the 
kallsysms_lookup_name(".funcname") gives us the function entry address, 
but the kallsyms_lookup_name("funcname") gives us the function 
descriptor. We want the latter case. See the reference
http://www.linuxbase.org/spec/ELF/ppc64/PPC-elf64abi-1.7.html#FUNC-DES

The patch should apply to the snapshoot systemtap-20052910.tar.bz2.


Hien.



--- src-20051029/runtime/runtime.h	2005-10-28 15:49:28.000000000 -0700
+++ src-20051029.works/runtime/runtime.h	2005-10-31 10:18:18.000000000 -0800
@@ -70,6 +70,10 @@
 					    unsigned long *symbolsize,
 					    unsigned long *offset,
 					    char **modname, char *namebuf);
+#if defined (__powerpc64__)
+static int (*_stp_validate_sp)(unsigned long sp, struct task_struct *p,
+				unsigned long nbytes);
+#endif
 
 /* TEST_MODE is always defined by systemtap */
 #ifdef TEST_MODE
@@ -131,8 +135,21 @@
 #endif
 int init_module (void)
 {
+/*
+ * In order for the kallsyms_lookup_name hack to work under ppc64, we need
+ * CONFIG_KALLSYMS_ALL=y.
+ * On ppc64 the kallsyms_lookup_name(.funcname) returns the function entry,
+ * but kallsyms_lookup_name(funcname) returns the function descriptor
+ * (func_descr_t). The latter is what we want, and those symbols are only
+ * available with CONFIG_KALLSYMS_ALL=y.
+ */
   _stp_kta = (int (*)(unsigned long))kallsyms_lookup_name("__kernel_text_address");
 
+#if defined (__powerpc64__)
+_stp_validate_sp = (int (*)(unsigned long, struct task_struct *,
+		unsigned long)) kallsyms_lookup_name("validate_sp");
+#endif
+
 #ifdef SYSTEMTAP
   if (stap_num_symbols > 0)
     _stp_kallsyms_lookup = & _stp_kallsyms_lookup_tabled;
--- src-20051029/runtime/stack.c	2005-10-28 15:49:28.000000000 -0700
+++ src-20051029.works/runtime/stack.c	2005-10-31 10:31:50.000000000 -0800
@@ -161,7 +161,77 @@
 			break;
 	}
 }
+#elif defined (__powerpc64__)
+static int kstack_depth_to_print = 5;
 
+static void __stp_stack_sprint (String str, unsigned long *_sp,
+				int verbose, int levels)
+{
+	struct task_struct *p = current;
+	unsigned long ip, newsp, lr = 0;
+	int count = 0;
+	unsigned long sp = (unsigned long)_sp;
+	int firstframe = 1;
+	
+	if (sp == 0) {
+		if (p) {
+			sp = p->thread.ksp;
+		} else {
+			sp = __get_SP();
+			p = current;
+		}
+	}
+	
+	if (!_stp_validate_sp)
+		return;
+
+	lr = 0;
+	do {
+		if (!_stp_validate_sp(sp, p, 112))
+			return;
+
+		_sp = (unsigned long *) sp;
+		newsp = _sp[0];
+		ip = _sp[2];
+		if (!firstframe || ip != lr) {
+			if (verbose) {
+				_stp_sprintf(str, "[%016lx] [%016lx] ", sp, ip);
+				_stp_symbol_sprint(str, ip);
+				if (firstframe)
+					_stp_string_cat(str, " (unreliable)");
+			}
+			else
+				_stp_sprintf(str,"%lx ", ip);
+		}
+		firstframe = 0;
+		/*
+		 * See if this is an exception frame.
+		 * We look for the "regshere" marker in the current frame.
+		 */
+		if (_stp_validate_sp(sp, p, sizeof(struct pt_regs) + 400)
+			&& _sp[12] == 0x7265677368657265ul) {
+			struct pt_regs *regs = (struct pt_regs *)
+				(sp + STACK_FRAME_OVERHEAD);
+			if (verbose) {
+				_stp_sprintf(str, "--- Exception: %lx at ",
+						regs->trap);
+				_stp_symbol_sprint(str, regs->nip);
+				_stp_string_cat(str, "\n");
+				lr = regs->link;
+				_stp_string_cat(str, "    LR =");
+				_stp_symbol_sprint(str, lr);
+				_stp_string_cat(str, "\n");
+				firstframe = 1;
+			}
+			else {
+				_stp_sprintf(str, "%lx ",regs->nip);
+				_stp_sprintf(str, "%lx ",regs->link);
+			}
+		}
+
+		sp = newsp;
+	} while (count++ < kstack_depth_to_print);
+}
 
 #else
 #error "Unsupported architecture"