powerpc/64: Drop ppc_inst_as_str()

The ppc_inst_as_str() macro tries to make printing variable length,
aka "prefixed", instructions convenient. It mostly succeeds, but it does
hide an on-stack buffer, which triggers stack protector.

More problematically it doesn't compile at all with GCC 12,
with -Wdangling-pointer, due to the fact that it returns the char buffer
declared inside the macro:

  arch/powerpc/kernel/trace/ftrace.c: In function '__ftrace_modify_call':
  ./include/linux/printk.h:475:44: error: using a dangling pointer to '__str' [-Werror=dangling-pointer=]
    475 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
    ...
  arch/powerpc/kernel/trace/ftrace.c:567:17: note: in expansion of macro 'pr_err'
    567 |                 pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op));
        |                 ^~~~~~
  ./arch/powerpc/include/asm/inst.h:156:14: note: '__str' declared here
    156 |         char __str[PPC_INST_STR_LEN];   \
        |              ^~~~~

This could be fixed by having the caller declare the buffer, but in some
places there'd need to be two buffers. In all cases where
ppc_inst_as_str() is used the output is not really meant for user
consumption, it's almost always indicative of a kernel bug.

A simpler solution is to just print the value as an unsigned long. For
normal instructions the output is identical. For prefixed instructions
the value is printed as a single 64-bit quantity, whereas previously the
low half was printed first. But that is good enough for debug output,
especially as prefixed instructions will be rare in kernel code in
practice.

Old:
  c000000000111170  60420000      ori     r2,r2,0
  c000000000111174  04100001 e580fb00     .long 0xe580fb0004100001

New:
  c00000000010f90c  60420000      ori     r2,r2,0
  c00000000010f910  e580fb0004100001      .long 0xe580fb0004100001

Reported-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reported-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20220531065936.3674348-1-mpe@ellerman.id.au

arch/powerpc/include/asm/inst.h

@@ -139,25 +139,6 @@ static inline void ppc_inst_write(u32 *ptr, ppc_inst_t x)
 		*(u64 *)ptr = ppc_inst_as_ulong(x);
 }
 
-#define PPC_INST_STR_LEN sizeof("00000000 00000000")
-
-static inline char *__ppc_inst_as_str(char str[PPC_INST_STR_LEN], ppc_inst_t x)
-{
-	if (ppc_inst_prefixed(x))
-		sprintf(str, "%08x %08x", ppc_inst_val(x), ppc_inst_suffix(x));
-	else
-		sprintf(str, "%08x", ppc_inst_val(x));
-
-	return str;
-}
-
-#define ppc_inst_as_str(x)		\
-({					\
-	char __str[PPC_INST_STR_LEN];	\
-	__ppc_inst_as_str(__str, x);	\
-	__str;				\
-})
-
 static inline int __copy_inst_from_kernel_nofault(ppc_inst_t *inst, u32 *src)
 {
 	unsigned int val, suffix;

arch/powerpc/kernel/kprobes.c

@@ -269,7 +269,7 @@ static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
 		 * So, we should never get here... but, its still
 		 * good to catch them, just in case...
 		 */
-		printk("Can't step on instruction %s\n", ppc_inst_as_str(insn));
+		printk("Can't step on instruction %08lx\n", ppc_inst_as_ulong(insn));
 		BUG();
 	} else {
 		/*

arch/powerpc/kernel/trace/ftrace.c

@@ -69,8 +69,8 @@ ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
 
 	/* Make sure it is what we expect it to be */
 	if (!ppc_inst_equal(replaced, old)) {
-		pr_err("%p: replaced (%s) != old (%s)",
-		(void *)ip, ppc_inst_as_str(replaced), ppc_inst_as_str(old));
+		pr_err("%p: replaced (%08lx) != old (%08lx)", (void *)ip,
+		       ppc_inst_as_ulong(replaced), ppc_inst_as_ulong(old));
 		return -EINVAL;
 	}
 
@@ -127,7 +127,7 @@ __ftrace_make_nop(struct module *mod,
 
 	/* Make sure that that this is still a 24bit jump */
 	if (!is_bl_op(op)) {
-		pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op));
+		pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
 		return -EINVAL;
 	}
 
@@ -159,8 +159,8 @@ __ftrace_make_nop(struct module *mod,
 		/* We expect either a mflr r0, or a std r0, LRSAVE(r1) */
 		if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_MFLR(_R0))) &&
 		    !ppc_inst_equal(op, ppc_inst(PPC_INST_STD_LR))) {
-			pr_err("Unexpected instruction %s around bl _mcount\n",
-			       ppc_inst_as_str(op));
+			pr_err("Unexpected instruction %08lx around bl _mcount\n",
+			       ppc_inst_as_ulong(op));
 			return -EINVAL;
 		}
 	} else if (IS_ENABLED(CONFIG_PPC64)) {
@@ -174,7 +174,8 @@ __ftrace_make_nop(struct module *mod,
 		}
 
 		if (!ppc_inst_equal(op,  ppc_inst(PPC_INST_LD_TOC))) {
-			pr_err("Expected %08lx found %s\n", PPC_INST_LD_TOC, ppc_inst_as_str(op));
+			pr_err("Expected %08lx found %08lx\n", PPC_INST_LD_TOC,
+			       ppc_inst_as_ulong(op));
 			return -EINVAL;
 		}
 	}
@@ -312,7 +313,7 @@ static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)
 
 	/* Make sure that that this is still a 24bit jump */
 	if (!is_bl_op(op)) {
-		pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op));
+		pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
 		return -EINVAL;
 	}
 
@@ -416,8 +417,8 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 		return -EFAULT;
 
 	if (!expected_nop_sequence(ip, op[0], op[1])) {
-		pr_err("Unexpected call sequence at %p: %s %s\n",
-		ip, ppc_inst_as_str(op[0]), ppc_inst_as_str(op[1]));
+		pr_err("Unexpected call sequence at %p: %08lx %08lx\n", ip,
+		       ppc_inst_as_ulong(op[0]), ppc_inst_as_ulong(op[1]));
 		return -EINVAL;
 	}
 
@@ -486,7 +487,8 @@ static int __ftrace_make_call_kernel(struct dyn_ftrace *rec, unsigned long addr)
 	}
 
 	if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_NOP()))) {
-		pr_err("Unexpected call sequence at %p: %s\n", ip, ppc_inst_as_str(op));
+		pr_err("Unexpected call sequence at %p: %08lx\n",
+		       ip, ppc_inst_as_ulong(op));
 		return -EINVAL;
 	}
 
@@ -564,7 +566,7 @@ __ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 
 	/* Make sure that that this is still a 24bit jump */
 	if (!is_bl_op(op)) {
-		pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op));
+		pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));
 		return -EINVAL;
 	}
 

arch/powerpc/lib/test_emulate_step.c

@@ -1616,11 +1616,11 @@ static int __init emulate_compute_instr(struct pt_regs *regs,
 	if (analysed != 1 || GETTYPE(op.type) != COMPUTE) {
 		if (negative)
 			return -EFAULT;
-		pr_info("emulation failed, instruction = %s\n", ppc_inst_as_str(instr));
+		pr_info("emulation failed, instruction = %08lx\n", ppc_inst_as_ulong(instr));
 		return -EFAULT;
 	}
 	if (analysed == 1 && negative)
-		pr_info("negative test failed, instruction = %s\n", ppc_inst_as_str(instr));
+		pr_info("negative test failed, instruction = %08lx\n", ppc_inst_as_ulong(instr));
 	if (!negative)
 		emulate_update_regs(regs, &op);
 	return 0;
@@ -1637,7 +1637,7 @@ static int __init execute_compute_instr(struct pt_regs *regs,
 	/* Patch the NOP with the actual instruction */
 	patch_instruction_site(&patch__exec_instr, instr);
 	if (exec_instr(regs)) {
-		pr_info("execution failed, instruction = %s\n", ppc_inst_as_str(instr));
+		pr_info("execution failed, instruction = %08lx\n", ppc_inst_as_ulong(instr));
 		return -EFAULT;
 	}
 

arch/powerpc/xmon/xmon.c

@@ -3047,7 +3047,7 @@ generic_inst_dump(unsigned long adr, long count, int praddr,
 		dotted = 0;
 		last_inst = inst;
 		if (praddr)
-			printf(REG"  %s", adr, ppc_inst_as_str(inst));
+			printf(REG"  %08lx", adr, ppc_inst_as_ulong(inst));
 		printf("\t");
 		if (!ppc_inst_prefixed(inst))
 			dump_func(ppc_inst_val(inst), adr);