libdrgn: Add find_symbol_by_name to look up ELF symbols

docs/api_reference.rst

@@ -128,11 +128,13 @@ Programs
         :raises LookupError: if no objects with the given name are found in
             the given file
 
-    .. method:: symbol(address)
+    .. method:: symbol(address_or_name, /)
 
-        Get the symbol containing the given address.
+        Get the symbol containing the given address, or the global symbol with
+        the given name.
 
-        :param int address: The address.
+        :param address_or_name: The address or name.
+        :type address_or_name: str or int
         :rtype: Symbol
         :raises LookupError: if no symbol contains the given address
 

libdrgn/drgn.h.in

@@ -1325,6 +1325,17 @@ struct drgn_error *
 drgn_program_find_symbol_by_address(struct drgn_program *prog, uint64_t address,
 				    struct drgn_symbol **ret);
 
+/**
+ * Get the symbol corresponding to the given name.
+ *
+ * @param[out] ret The returned symbol. It should be freed with @ref
+ * drgn_symbol_destroy().
+ * @return @c NULL on success, non-@c NULL on error.
+ */
+struct drgn_error *drgn_program_find_symbol_by_name(struct drgn_program *prog,
+						    const char *name,
+						    struct drgn_symbol **ret);
+
 /** Element type and size. */
 struct drgn_element_info {
 	/** Type of the element. */

libdrgn/program.c

@@ -961,6 +961,70 @@ drgn_program_find_symbol_by_address(struct drgn_program *prog, uint64_t address,
 	return NULL;
 }
 
+struct find_symbol_by_name_arg {
+	const char *name;
+	struct drgn_symbol **ret;
+	struct drgn_error *err;
+	bool bad_symtabs;
+};
+
+static int find_symbol_by_name_cb(Dwfl_Module *dwfl_module, void **userdatap,
+				  const char *module_name, Dwarf_Addr base,
+				  void *cb_arg)
+{
+	struct find_symbol_by_name_arg *arg = cb_arg;
+	int symtab_len, i;
+
+	symtab_len = dwfl_module_getsymtab(dwfl_module);
+	i = dwfl_module_getsymtab_first_global(dwfl_module);
+	if (symtab_len == -1 || i == -1) {
+		arg->bad_symtabs = true;
+		return DWARF_CB_OK;
+	}
+	for (; i < symtab_len; i++) {
+		GElf_Sym elf_sym;
+		GElf_Addr elf_addr;
+		const char *name;
+
+		name = dwfl_module_getsym_info(dwfl_module, i, &elf_sym,
+					       &elf_addr, NULL, NULL, NULL);
+		if (name && strcmp(arg->name, name) == 0) {
+			struct drgn_symbol *sym;
+
+			sym = malloc(sizeof(*sym));
+			if (sym) {
+				sym->name = name;
+				sym->address = elf_addr;
+				sym->size = elf_sym.st_size;
+				*arg->ret = sym;
+			} else {
+				arg->err = &drgn_enomem;
+			}
+			return DWARF_CB_ABORT;
+		}
+	}
+	return DWARF_CB_OK;
+}
+
+LIBDRGN_PUBLIC struct drgn_error *
+drgn_program_find_symbol_by_name(struct drgn_program *prog,
+			const char *name, struct drgn_symbol **ret)
+{
+	struct find_symbol_by_name_arg arg = {
+		.name = name,
+		.ret = ret,
+	};
+
+	if (prog->_dicache &&
+	    dwfl_getmodules(prog->_dicache->dindex.dwfl, find_symbol_by_name_cb,
+			    &arg, 0))
+		return arg.err;
+	return drgn_error_format(DRGN_ERROR_LOOKUP,
+				 "could not find symbol with name '%s'%s", name,
+				 arg.bad_symtabs ?
+				 " (could not get some symbol tables)" : "");
+}
+
 LIBDRGN_PUBLIC struct drgn_error *
 drgn_program_element_info(struct drgn_program *prog, struct drgn_type *type,
 			  struct drgn_element_info *ret)

libdrgn/python/program.c

@@ -718,20 +718,27 @@ static StackTrace *Program_stack_trace(Program *self, PyObject *args,
 	return ret;
 }
 
-static PyObject *Program_symbol(Program *self, PyObject *args, PyObject *kwds)
+static PyObject *Program_symbol(Program *self, PyObject *arg)
 {
-	static char *keywords[] = {"address", NULL};
 	struct drgn_error *err;
-	struct index_arg address = {};
 	struct drgn_symbol *sym;
 	PyObject *ret;
 
-	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&", keywords,
-					 index_converter, &address))
-		return NULL;
+	if (PyUnicode_Check(arg)) {
+		const char *name;
 
-	err = drgn_program_find_symbol_by_address(&self->prog, address.uvalue,
-						  &sym);
+		name = PyUnicode_AsUTF8(arg);
+		if (!name)
+			return NULL;
+		err = drgn_program_find_symbol_by_name(&self->prog, name, &sym);
+	} else {
+		struct index_arg address = {};
+
+		if (!index_converter(arg, &address))
+			return NULL;
+		err = drgn_program_find_symbol_by_address(&self->prog,
+							  address.uvalue, &sym);
+	}
 	if (err)
 		return set_drgn_error(err);
 	ret = Symbol_wrap(sym, self);
@@ -868,7 +875,7 @@ static PyMethodDef Program_methods[] = {
 	 METH_VARARGS | METH_KEYWORDS, drgn_Program_variable_DOC},
 	{"stack_trace", (PyCFunction)Program_stack_trace,
 	 METH_VARARGS | METH_KEYWORDS, drgn_Program_stack_trace_DOC},
-	{"symbol", (PyCFunction)Program_symbol, METH_VARARGS | METH_KEYWORDS,
+	{"symbol", (PyCFunction)Program_symbol, METH_O,
 	 drgn_Program_symbol_DOC},
 	{},
 };