[PATCH v2 1/2] powerpc/ftrace: Simplify error checking when patching instructions

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Introduce a macro PATCH_INSN_OR_GOTO() to simplify instruction patching,
and to make the error messages more uniform and useful:
- print an error message that includes the original return value
- print the function name and line numbers, so that the offending
  location is clear
- goto a label which always return -EPERM, which ftrace_bug() expects
  for proper error handling

Also eliminate use of patch_branch() since most such uses already call
create_branch() for error checking before patching. Instead, use the
return value from create_branch() with PATCH_INSN_OR_GOTO().

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/trace/ftrace.c | 96 +++++++++++++++++++-----------
 1 file changed, 60 insertions(+), 36 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 7ea0ca044b65..63edbd48af42 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -31,6 +31,17 @@
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 
+#define PATCH_INSN_OR_GOTO(addr, instr, label)				     \
+do {									     \
+	int rc = patch_instruction((unsigned int *)(addr), instr);	     \
+	if (rc) {							     \
+		pr_err("%s:%d Error patching instruction at 0x%pK (%pS): %d\n", \
+				__func__, __LINE__,			     \
+				(void *)(addr), (void *)(addr), rc);	     \
+		goto label;						     \
+	}								     \
+} while (0)
+
 /*
  * We generally only have a single long_branch tramp and at most 2 or 3 plt
  * tramps generated. But, we don't use the plt tramps currently. We also allot
@@ -78,10 +89,12 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new)
 	}
 
 	/* replace the text with the new text */
-	if (patch_instruction((unsigned int *)ip, new))
-		return -EPERM;
+	PATCH_INSN_OR_GOTO(ip, new, patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 
 /*
@@ -204,12 +217,12 @@ __ftrace_make_nop(struct module *mod,
 	}
 #endif /* CONFIG_MPROFILE_KERNEL */
 
-	if (patch_instruction((unsigned int *)ip, pop)) {
-		pr_err("Patching NOP failed.\n");
-		return -EPERM;
-	}
+	PATCH_INSN_OR_GOTO(ip, pop, patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 
 #else /* !PPC64 */
@@ -276,10 +289,12 @@ __ftrace_make_nop(struct module *mod,
 
 	op = PPC_INST_NOP;
 
-	if (patch_instruction((unsigned int *)ip, op))
-		return -EPERM;
+	PATCH_INSN_OR_GOTO(ip, op, patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 #endif /* PPC64 */
 #endif /* CONFIG_MODULES */
@@ -322,7 +337,7 @@ static int add_ftrace_tramp(unsigned long tramp)
  */
 static int setup_mcount_compiler_tramp(unsigned long tramp)
 {
-	int i, op;
+	unsigned int i, op;
 	unsigned long ptr;
 	static unsigned long ftrace_plt_tramps[NUM_FTRACE_TRAMPS];
 
@@ -366,16 +381,14 @@ static int setup_mcount_compiler_tramp(unsigned long tramp)
 #else
 	ptr = ppc_global_function_entry((void *)ftrace_caller);
 #endif
-	if (!create_branch((void *)tramp, ptr, 0)) {
+	op = create_branch((void *)tramp, ptr, 0);
+	if (!op) {
 		pr_debug("%ps is not reachable from existing mcount tramp\n",
 				(void *)ptr);
 		return -1;
 	}
 
-	if (patch_branch((unsigned int *)tramp, ptr, 0)) {
-		pr_debug("REL24 out of range!\n");
-		return -1;
-	}
+	PATCH_INSN_OR_GOTO(tramp, op, patch_err);
 
 	if (add_ftrace_tramp(tramp)) {
 		pr_debug("No tramp locations left\n");
@@ -383,6 +396,9 @@ static int setup_mcount_compiler_tramp(unsigned long tramp)
 	}
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 
 static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)
@@ -416,12 +432,12 @@ static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)
 		}
 	}
 
-	if (patch_instruction((unsigned int *)ip, PPC_INST_NOP)) {
-		pr_err("Patching NOP failed.\n");
-		return -EPERM;
-	}
+	PATCH_INSN_OR_GOTO(ip, PPC_INST_NOP, patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 
 int ftrace_make_nop(struct module *mod,
@@ -557,17 +573,18 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	}
 
 	/* Ensure branch is within 24 bits */
-	if (!create_branch(ip, tramp, BRANCH_SET_LINK)) {
+	op[0] = create_branch(ip, tramp, BRANCH_SET_LINK);
+	if (!op[0]) {
 		pr_err("Branch out of range\n");
 		return -EINVAL;
 	}
 
-	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {
-		pr_err("REL24 out of range!\n");
-		return -EINVAL;
-	}
+	PATCH_INSN_OR_GOTO(ip, op[0], patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 
 #else  /* !CONFIG_PPC64: */
@@ -603,10 +620,12 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 
 	pr_devel("write to %lx\n", rec->ip);
 
-	if (patch_instruction((unsigned int *)ip, op))
-		return -EPERM;
+	PATCH_INSN_OR_GOTO(ip, op, patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 #endif /* CONFIG_PPC64 */
 #endif /* CONFIG_MODULES */
@@ -650,12 +669,18 @@ static int __ftrace_make_call_kernel(struct dyn_ftrace *rec, unsigned long addr)
 		return -EINVAL;
 	}
 
-	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {
-		pr_err("Error patching branch to ftrace tramp!\n");
+	op = create_branch(ip, tramp, BRANCH_SET_LINK);
+	if (!op) {
+		pr_err("Branch out of range\n");
 		return -EINVAL;
 	}
 
+	PATCH_INSN_OR_GOTO(ip, op, patch_err);
+
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
@@ -748,10 +773,8 @@ __ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 	/* The new target may be within range */
 	if (test_24bit_addr(ip, addr)) {
 		/* within range */
-		if (patch_branch((unsigned int *)ip, addr, BRANCH_SET_LINK)) {
-			pr_err("REL24 out of range!\n");
-			return -EINVAL;
-		}
+		op = create_branch((unsigned int *)ip, addr, BRANCH_SET_LINK);
+		PATCH_INSN_OR_GOTO(ip, op, patch_err);
 
 		return 0;
 	}
@@ -776,17 +799,18 @@ __ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 	}
 
 	/* Ensure branch is within 24 bits */
-	if (!create_branch((unsigned int *)ip, tramp, BRANCH_SET_LINK)) {
+	op = create_branch((unsigned int *)ip, tramp, BRANCH_SET_LINK);
+	if (!op) {
 		pr_err("Branch out of range\n");
 		return -EINVAL;
 	}
 
-	if (patch_branch((unsigned int *)ip, tramp, BRANCH_SET_LINK)) {
-		pr_err("REL24 out of range!\n");
-		return -EINVAL;
-	}
+	PATCH_INSN_OR_GOTO(ip, op, patch_err);
 
 	return 0;
+
+patch_err:
+	return -EPERM;
 }
 #endif
 
-- 
2.25.1