objtool: Improve register reporting during function validation

When tracing function validation, instruction state changes can
report changes involving registers. These registers are reported
with the name "r<num>" (e.g. "r3"). Print the CPU specific register
name instead of a generic name (e.g. print "rbx" instead of "r3"
on x86).

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/20251121095340.464045-13-alexandre.chartre@oracle.com

tools/objtool/arch/loongarch/decode.c

@@ -8,6 +8,17 @@
 #include <linux/objtool_types.h>
 #include <arch/elf.h>
 
+const char *arch_reg_name[CFI_NUM_REGS] = {
+	"zero", "ra", "tp", "sp",
+	"a0", "a1", "a2", "a3",
+	"a4", "a5", "a6", "a7",
+	"t0", "t1", "t2", "t3",
+	"t4", "t5", "t6", "t7",
+	"t8", "u0", "fp", "s0",
+	"s1", "s2", "s3", "s4",
+	"s5", "s6", "s7", "s8"
+};
+
 int arch_ftrace_match(const char *name)
 {
 	return !strcmp(name, "_mcount");

tools/objtool/arch/powerpc/decode.c

@@ -9,6 +9,18 @@
 #include <objtool/warn.h>
 #include <objtool/builtin.h>
 
+const char *arch_reg_name[CFI_NUM_REGS] = {
+	"r0",  "sp",  "r2",  "r3",
+	"r4",  "r5",  "r6",  "r7",
+	"r8",  "r9",  "r10", "r11",
+	"r12", "r13", "r14", "r15",
+	"r16", "r17", "r18", "r19",
+	"r20", "r21", "r22", "r23",
+	"r24", "r25", "r26", "r27",
+	"r28", "r29", "r30", "r31",
+	"ra"
+};
+
 int arch_ftrace_match(const char *name)
 {
 	return !strcmp(name, "_mcount");

tools/objtool/arch/x86/decode.c

@@ -23,6 +23,14 @@
 #include <objtool/builtin.h>
 #include <arch/elf.h>
 
+const char *arch_reg_name[CFI_NUM_REGS] = {
+	"rax", "rcx", "rdx", "rbx",
+	"rsp", "rbp", "rsi", "rdi",
+	"r8",  "r9",  "r10", "r11",
+	"r12", "r13", "r14", "r15",
+	"ra"
+};
+
 int arch_ftrace_match(const char *name)
 {
 	return !strcmp(name, "__fentry__");

tools/objtool/include/objtool/arch.h

@@ -103,6 +103,8 @@ bool arch_absolute_reloc(struct elf *elf, struct reloc *reloc);
 unsigned int arch_reloc_size(struct reloc *reloc);
 unsigned long arch_jump_table_sym_offset(struct reloc *reloc, struct reloc *table);
 
+extern const char *arch_reg_name[CFI_NUM_REGS];
+
 #ifdef DISAS
 
 #include <bfd.h>

tools/objtool/trace.c

@@ -34,6 +34,7 @@ int trace_depth;
 static const char *cfi_reg_name(unsigned int reg)
 {
 	static char rname_buffer[CFI_REG_NAME_MAXLEN];
+	const char *rname;
 
 	switch (reg) {
 	case CFI_UNDEFINED:
@@ -46,6 +47,12 @@ static const char *cfi_reg_name(unsigned int reg)
 		return "(bp)";
 	}
 
+	if (reg < CFI_NUM_REGS) {
+		rname = arch_reg_name[reg];
+		if (rname)
+			return rname;
+	}
+
 	if (snprintf(rname_buffer, CFI_REG_NAME_MAXLEN, "r%d", reg) == -1)
 		return "<error>";