binman: Support reading the offset of an ELF-file symbol

Binman needs to be able to update the contents of an ELF file after it has
been build. To support this, add a function to locate the position of a
symbol's contents within the file.

Fix the comments on bss_data.c and Symbol while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/Makefile b/tools/binman/test/Makefile
index 0b19b7d..6e6cc6d 100644
--- a/tools/binman/test/Makefile
+++ b/tools/binman/test/Makefile
@@ -31,7 +31,7 @@
 
 TARGETS = u_boot_ucode_ptr u_boot_no_ucode_ptr bss_data \
 	u_boot_binman_syms u_boot_binman_syms.bin u_boot_binman_syms_bad \
-	u_boot_binman_syms_size u_boot_binman_syms_x86
+	u_boot_binman_syms_size u_boot_binman_syms_x86 embed_data
 
 all: $(TARGETS)
 
@@ -44,6 +44,9 @@
 bss_data: CFLAGS += $(SRC)bss_data.lds
 bss_data: bss_data.c
 
+embed_data: CFLAGS += $(SRC)embed_data.lds
+embed_data: embed_data.c
+
 u_boot_binman_syms.bin: u_boot_binman_syms
 	$(OBJCOPY) -O binary $< -R .note.gnu.build-id $@
 
diff --git a/tools/binman/test/bss_data.c b/tools/binman/test/bss_data.c
index 79537c3..4f9b64c 100644
--- a/tools/binman/test/bss_data.c
+++ b/tools/binman/test/bss_data.c
@@ -2,7 +2,7 @@
 /*
  * Copyright (c) 2016 Google, Inc
  *
- * Simple program to create a _dt_ucode_base_size symbol which can be read
+ * Simple program to create a bss_data region so the symbol can be read
  * by binutils. This is used by binman tests.
  */
 
diff --git a/tools/binman/test/embed_data.c b/tools/binman/test/embed_data.c
new file mode 100644
index 0000000..47d8c38
--- /dev/null
+++ b/tools/binman/test/embed_data.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Simple program including some embedded data that can be accessed by binman.
+ * This is used by binman tests.
+ */
+
+int first[10] = {1};
+int embed[3] __attribute__((section(".embed"))) = {0x1234, 0x5678};
+int second[10] = {1};
+
+int main(void)
+{
+	return 0;
+}
diff --git a/tools/binman/test/embed_data.lds b/tools/binman/test/embed_data.lds
new file mode 100644
index 0000000..908bf66
--- /dev/null
+++ b/tools/binman/test/embed_data.lds
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2021 Google LLC
+ */
+
+OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
+OUTPUT_ARCH(i386)
+ENTRY(_start)
+
+SECTIONS
+{
+	_start = .;
+	__data_start = .;
+	.data :
+	{
+		. = ALIGN(32);
+		embed_start = .;
+		*(.embed*)
+		embed_end = .;
+		. = ALIGN(32);
+		*(.data*)
+	}
+}