powerpc: Change calling convention for create_branch() et. al.

create_branch(), create_cond_branch() and translate_branch() return the
instruction that they create, or return 0 to signal an error. Separate
these concerns in preparation for an instruction type that is not just
an unsigned int.  Fill the created instruction to a pointer passed as
the first parameter to the function and use a non-zero return value to
signify an error.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Alistair Popple <alistair@popple.id.au>
Link: https://lore.kernel.org/r/20200506034050.24806-6-jniethe5@gmail.com

arch/powerpc/include/asm/code-patching.h

@@ -22,9 +22,9 @@
 #define BRANCH_ABSOLUTE	0x2
 
 bool is_offset_in_branch_range(long offset);
-unsigned int create_branch(const unsigned int *addr,
+int create_branch(unsigned int *instr, const unsigned int *addr,
 		  unsigned long target, int flags);
-unsigned int create_cond_branch(const unsigned int *addr,
+int create_cond_branch(unsigned int *instr, const unsigned int *addr,
 		       unsigned long target, int flags);
 int patch_branch(unsigned int *addr, unsigned long target, int flags);
 int patch_instruction(unsigned int *addr, unsigned int instr);
@@ -60,7 +60,7 @@ int instr_is_relative_branch(unsigned int instr);
 int instr_is_relative_link_branch(unsigned int instr);
 int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr);
 unsigned long branch_target(const unsigned int *instr);
-unsigned int translate_branch(const unsigned int *dest,
+int translate_branch(unsigned int *instr, const unsigned int *dest,
 		     const unsigned int *src);
 extern bool is_conditional_branch(unsigned int instr);
 #ifdef CONFIG_PPC_BOOK3E_64

arch/powerpc/kernel/optprobes.c

@@ -251,15 +251,17 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 		goto error;
 	}
 
-	branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
+	rc = create_branch(&branch_op_callback,
+			   (unsigned int *)buff + TMPL_CALL_HDLR_IDX,
 			   (unsigned long)op_callback_addr,
 			   BRANCH_SET_LINK);
 
-	branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
+	rc |= create_branch(&branch_emulate_step,
+			    (unsigned int *)buff + TMPL_EMULATE_IDX,
 			    (unsigned long)emulate_step_addr,
 			    BRANCH_SET_LINK);
 
-	if (!branch_op_callback || !branch_emulate_step)
+	if (rc)
 		goto error;
 
 	patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
@@ -305,6 +307,7 @@ int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 
 void arch_optimize_kprobes(struct list_head *oplist)
 {
+	unsigned int instr;
 	struct optimized_kprobe *op;
 	struct optimized_kprobe *tmp;
 
@@ -315,9 +318,10 @@ void arch_optimize_kprobes(struct list_head *oplist)
 		 */
 		memcpy(op->optinsn.copied_insn, op->kp.addr,
 					       RELATIVEJUMP_SIZE);
-		patch_instruction(op->kp.addr,
-			create_branch((unsigned int *)op->kp.addr,
-				      (unsigned long)op->optinsn.insn, 0));
+		create_branch(&instr,
+			      (unsigned int *)op->kp.addr,
+			      (unsigned long)op->optinsn.insn, 0);
+		patch_instruction(op->kp.addr, instr);
 		list_del_init(&op->list);
 	}
 }

arch/powerpc/kernel/setup_32.c

@@ -75,7 +75,7 @@ EXPORT_SYMBOL(DMA_MODE_WRITE);
 notrace void __init machine_init(u64 dt_ptr)
 {
 	unsigned int *addr = (unsigned int *)patch_site_addr(&patch__memset_nocache);
-	unsigned long insn;
+	unsigned int insn;
 
 	/* Configure static keys first, now that we're relocated. */
 	setup_feature_keys();
@@ -87,7 +87,7 @@ notrace void __init machine_init(u64 dt_ptr)
 
 	patch_instruction_site(&patch__memcpy_nocache, PPC_INST_NOP);
 
-	insn = create_cond_branch(addr, branch_target(addr), 0x820000);
+	create_cond_branch(&insn, addr, branch_target(addr), 0x820000);
 	patch_instruction(addr, insn);	/* replace b by bne cr0 */
 
 	/* Do some early initialization based on the flat device tree */

arch/powerpc/kernel/trace/ftrace.c

@@ -48,7 +48,7 @@ ftrace_call_replace(unsigned long ip, unsigned long addr, int link)
 	addr = ppc_function_entry((void *)addr);
 
 	/* if (link) set op to 'bl' else 'b' */
-	op = create_branch((unsigned int *)ip, addr, link ? 1 : 0);
+	create_branch(&op, (unsigned int *)ip, addr, link ? 1 : 0);
 
 	return op;
 }
@@ -89,10 +89,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new)
  */
 static int test_24bit_addr(unsigned long ip, unsigned long addr)
 {
+	unsigned int op;
 	addr = ppc_function_entry((void *)addr);
 
 	/* use the create_branch to verify that this offset can be branched */
-	return create_branch((unsigned int *)ip, addr, 0);
+	return create_branch(&op, (unsigned int *)ip, addr, 0) == 0;
 }
 
 static int is_bl_op(unsigned int op)
@@ -287,6 +288,7 @@ __ftrace_make_nop(struct module *mod,
 static unsigned long find_ftrace_tramp(unsigned long ip)
 {
 	int i;
+	unsigned int instr;
 
 	/*
 	 * We have the compiler generated long_branch tramps at the end
@@ -295,7 +297,8 @@ static unsigned long find_ftrace_tramp(unsigned long ip)
 	for (i = NUM_FTRACE_TRAMPS - 1; i >= 0; i--)
 		if (!ftrace_tramps[i])
 			continue;
-		else if (create_branch((void *)ip, ftrace_tramps[i], 0))
+		else if (create_branch(&instr, (void *)ip,
+				       ftrace_tramps[i], 0) == 0)
 			return ftrace_tramps[i];
 
 	return 0;
@@ -324,6 +327,7 @@ static int setup_mcount_compiler_tramp(unsigned long tramp)
 {
 	int i, op;
 	unsigned long ptr;
+	unsigned int instr;
 	static unsigned long ftrace_plt_tramps[NUM_FTRACE_TRAMPS];
 
 	/* Is this a known long jump tramp? */
@@ -366,7 +370,7 @@ 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)) {
+	if (create_branch(&instr, (void *)tramp, ptr, 0)) {
 		pr_debug("%ps is not reachable from existing mcount tramp\n",
 				(void *)ptr);
 		return -1;
@@ -511,6 +515,7 @@ static int
 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned int op[2];
+	unsigned int instr;
 	void *ip = (void *)rec->ip;
 	unsigned long entry, ptr, tramp;
 	struct module *mod = rec->arch.mod;
@@ -557,7 +562,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	}
 
 	/* Ensure branch is within 24 bits */
-	if (!create_branch(ip, tramp, BRANCH_SET_LINK)) {
+	if (create_branch(&instr, ip, tramp, BRANCH_SET_LINK)) {
 		pr_err("Branch out of range\n");
 		return -EINVAL;
 	}
@@ -574,6 +579,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 static int
 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
+	int err;
 	unsigned int op;
 	unsigned long ip = rec->ip;
 
@@ -594,9 +600,9 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	}
 
 	/* create the branch to the trampoline */
-	op = create_branch((unsigned int *)ip,
+	err = create_branch(&op, (unsigned int *)ip,
 			    rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
-	if (!op) {
+	if (err) {
 		pr_err("REL24 out of range!\n");
 		return -EINVAL;
 	}
@@ -776,7 +782,7 @@ __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)) {
+	if (create_branch(&op, (unsigned int *)ip, tramp, BRANCH_SET_LINK)) {
 		pr_err("Branch out of range\n");
 		return -EINVAL;
 	}

arch/powerpc/lib/feature-fixups.c

@@ -44,6 +44,7 @@ static unsigned int *calc_addr(struct fixup_entry *fcur, long offset)
 static int patch_alt_instruction(unsigned int *src, unsigned int *dest,
 				 unsigned int *alt_start, unsigned int *alt_end)
 {
+	int err;
 	unsigned int instr;
 
 	instr = *src;
@@ -53,8 +54,8 @@ static int patch_alt_instruction(unsigned int *src, unsigned int *dest,
 
 		/* Branch within the section doesn't need translating */
 		if (target < alt_start || target > alt_end) {
-			instr = translate_branch(dest, src);
-			if (!instr)
+			err = translate_branch(&instr, dest, src);
+			if (err)
 				return 1;
 		}
 	}