objtool: Print symbol during disassembly

Print symbols referenced during disassembly instead of just printing
raw addresses. Also handle address relocation.

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/20251121095340.464045-6-alexandre.chartre@oracle.com

tools/objtool/check.c

@@ -134,15 +134,6 @@ static struct instruction *prev_insn_same_sym(struct objtool_file *file,
 	for (insn = next_insn_same_sec(file, insn); insn;		\
 	     insn = next_insn_same_sec(file, insn))
 
-static inline struct symbol *insn_call_dest(struct instruction *insn)
-{
-	if (insn->type == INSN_JUMP_DYNAMIC ||
-	    insn->type == INSN_CALL_DYNAMIC)
-		return NULL;
-
-	return insn->_call_dest;
-}
-
 static inline struct reloc *insn_jump_table(struct instruction *insn)
 {
 	if (insn->type == INSN_JUMP_DYNAMIC ||

tools/objtool/disas.c

@@ -14,13 +14,144 @@
 
 struct disas_context {
 	struct objtool_file *file;
+	struct instruction *insn;
 	disassembler_ftype disassembler;
 	struct disassemble_info info;
 };
 
+static int sprint_name(char *str, const char *name, unsigned long offset)
+{
+	int len;
+
+	if (offset)
+		len = sprintf(str, "%s+0x%lx", name, offset);
+	else
+		len = sprintf(str, "%s", name);
+
+	return len;
+}
+
 #define DINFO_FPRINTF(dinfo, ...)	\
 	((*(dinfo)->fprintf_func)((dinfo)->stream, __VA_ARGS__))
 
+static void disas_print_addr_sym(struct section *sec, struct symbol *sym,
+				 bfd_vma addr, struct disassemble_info *dinfo)
+{
+	char symstr[1024];
+	char *str;
+
+	if (sym) {
+		sprint_name(symstr, sym->name, addr - sym->offset);
+		DINFO_FPRINTF(dinfo, "0x%lx <%s>", addr, symstr);
+	} else {
+		str = offstr(sec, addr);
+		DINFO_FPRINTF(dinfo, "0x%lx <%s>", addr, str);
+		free(str);
+	}
+}
+
+static void disas_print_addr_noreloc(bfd_vma addr,
+				     struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *insn = dctx->insn;
+	struct symbol *sym = NULL;
+
+	if (insn->sym && addr >= insn->sym->offset &&
+	    addr < insn->sym->offset + insn->sym->len) {
+		sym = insn->sym;
+	}
+
+	disas_print_addr_sym(insn->sec, sym, addr, dinfo);
+}
+
+static void disas_print_addr_reloc(bfd_vma addr, struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *insn = dctx->insn;
+	unsigned long offset;
+	struct reloc *reloc;
+	char symstr[1024];
+	char *str;
+
+	reloc = find_reloc_by_dest_range(dctx->file->elf, insn->sec,
+					 insn->offset, insn->len);
+	if (!reloc) {
+		/*
+		 * There is no relocation for this instruction although
+		 * the address to resolve points to the next instruction.
+		 * So this is an effective reference to the next IP, for
+		 * example: "lea 0x0(%rip),%rdi". The kernel can reference
+		 * the next IP with _THIS_IP_ macro.
+		 */
+		DINFO_FPRINTF(dinfo, "0x%lx <_THIS_IP_>", addr);
+		return;
+	}
+
+	offset = arch_insn_adjusted_addend(insn, reloc);
+
+	/*
+	 * If the relocation symbol is a section name (for example ".bss")
+	 * then we try to further resolve the name.
+	 */
+	if (reloc->sym->type == STT_SECTION) {
+		str = offstr(reloc->sym->sec, reloc->sym->offset + offset);
+		DINFO_FPRINTF(dinfo, "0x%lx <%s>", addr, str);
+		free(str);
+	} else {
+		sprint_name(symstr, reloc->sym->name, offset);
+		DINFO_FPRINTF(dinfo, "0x%lx <%s>", addr, symstr);
+	}
+}
+
+/*
+ * Resolve an address into a "<symbol>+<offset>" string.
+ */
+static void disas_print_address(bfd_vma addr, struct disassemble_info *dinfo)
+{
+	struct disas_context *dctx = dinfo->application_data;
+	struct instruction *insn = dctx->insn;
+	struct instruction *jump_dest;
+	struct symbol *sym;
+	bool is_reloc;
+
+	/*
+	 * If the instruction is a call/jump and it references a
+	 * destination then this is likely the address we are looking
+	 * up. So check it first.
+	 */
+	jump_dest = insn->jump_dest;
+	if (jump_dest && jump_dest->sym && jump_dest->offset == addr) {
+		disas_print_addr_sym(jump_dest->sec, jump_dest->sym,
+				     addr, dinfo);
+		return;
+	}
+
+	/*
+	 * If the address points to the next instruction then there is
+	 * probably a relocation. It can be a false positive when the
+	 * current instruction is referencing the address of the next
+	 * instruction. This particular case will be handled in
+	 * disas_print_addr_reloc().
+	 */
+	is_reloc = (addr == insn->offset + insn->len);
+
+	/*
+	 * The call destination offset can be the address we are looking
+	 * up, or 0 if there is a relocation.
+	 */
+	sym = insn_call_dest(insn);
+	if (sym && (sym->offset == addr || (sym->offset == 0 && is_reloc))) {
+		DINFO_FPRINTF(dinfo, "0x%lx <%s>", addr, sym->name);
+		return;
+	}
+
+	if (!is_reloc)
+		disas_print_addr_noreloc(addr, dinfo);
+	else
+		disas_print_addr_reloc(addr, dinfo);
+}
+
 /*
  * Initialize disassemble info arch, mach (32 or 64-bit) and options.
  */
@@ -69,6 +200,7 @@ struct disas_context *disas_context_create(struct objtool_file *file)
 				     fprintf_styled);
 
 	dinfo->read_memory_func = buffer_read_memory;
+	dinfo->print_address_func = disas_print_address;
 	dinfo->application_data = dctx;
 
 	/*
@@ -121,6 +253,8 @@ static size_t disas_insn(struct disas_context *dctx,
 	disassembler_ftype disasm = dctx->disassembler;
 	struct disassemble_info *dinfo = &dctx->info;
 
+	dctx->insn = insn;
+
 	if (insn->type == INSN_NOP) {
 		DINFO_FPRINTF(dinfo, "nop%d", insn->len);
 		return insn->len;

tools/objtool/include/objtool/check.h

@@ -117,6 +117,15 @@ static inline bool is_jump(struct instruction *insn)
 	return is_static_jump(insn) || is_dynamic_jump(insn);
 }
 
+static inline struct symbol *insn_call_dest(struct instruction *insn)
+{
+	if (insn->type == INSN_JUMP_DYNAMIC ||
+	    insn->type == INSN_CALL_DYNAMIC)
+		return NULL;
+
+	return insn->_call_dest;
+}
+
 struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);