From e4bca8dc710e0d8df28b81562052a4e46ca7bf34 Mon Sep 17 00:00:00 2001
From: Xing GUO <higuoxing@gmail.com>
Date: Wed, 6 Mar 2019 01:28:40 +0000
Subject: [PATCH] [BinaryFormat] Add DT_USED tag into dynamic section.

Summary:
This tag is documented in https://docs.oracle.com/cd/E19253-01/817-1984/chapter6-42444/index.html
Though I could not find some docs that describe it in detail, I found some code snippets.

1.
```
	/*
	 * Look up the string in the string table and get its offset. If
	 * this succeeds, then it is possible that there is a DT_NEEDED
	 * dynamic entry that references it.
	 */
	have_string = elfedit_sec_findstr(argstate->str.sec,
	    strpad_elt.dn_dyn.d_un.d_val, arg, &str_offset) != 0;
	if (have_string) {
		dyn = argstate->dynamic.data;
		for (ndx = 0; ndx < numdyn; dyn++, ndx++) {
			if (((dyn->d_tag == DT_NEEDED) ||
			    (dyn->d_tag == DT_USED)) &&
			    (dyn->d_un.d_val == str_offset))
				goto done;
		}
	}
```
https://github.com/kofemann/opensolaris/blob/80192cd83bf665e708269dae856f9145f7190f74/usr/src/cmd/sgs/elfedit/modules/common/syminfo.c#L512

2.
```
    case DT_USED:
    case DT_INIT_ARRAY:
    case DT_FINI_ARRAY:
      if (do_dynamic)
        {
          if (entry->d_tag == DT_USED
          && VALID_DYNAMIC_NAME (entry->d_un.d_val))
        {
          char *name = GET_DYNAMIC_NAME (entry->d_un.d_val);

          if (*name)
            {
              printf (_("Not needed object: [%s]\n"), name);
              break;
            }
        }

          print_vma (entry->d_un.d_val, PREFIX_HEX);
          putchar ('\n');
        }
      break;
```
http://web.mit.edu/freebsd/head/contrib/binutils/binutils/readelf.c

3.
```
#define DT_USED     0x7ffffffe  /* ignored - same as needed */
```
https://github.com/switchbrew/switch-tools/blob/master/src/elf_common.h

Reviewers: jhenderson, grimar

Reviewed By: jhenderson, grimar

Subscribers: emaste, krytarowski, fedor.sergeev, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58762

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355468 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/BinaryFormat/DynamicTags.def | 1 +
 test/tools/obj2yaml/dynamic-section.test  | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/llvm/BinaryFormat/DynamicTags.def b/include/llvm/BinaryFormat/DynamicTags.def
index 3f9b7b80b61..82fe72eefad 100644
--- a/include/llvm/BinaryFormat/DynamicTags.def
+++ b/include/llvm/BinaryFormat/DynamicTags.def
@@ -196,6 +196,7 @@ PPC64_DYNAMIC_TAG(PPC64_GLINK, 0x70000000) // Address of 32 bytes before the
 
 // Sun machine-independent extensions.
 DYNAMIC_TAG(AUXILIARY, 0x7FFFFFFD) // Shared object to load before self
+DYNAMIC_TAG(USED, 0x7FFFFFFE)      // Same as DT_NEEDED
 DYNAMIC_TAG(FILTER, 0x7FFFFFFF)    // Shared object to get values from
 
 
diff --git a/test/tools/obj2yaml/dynamic-section.test b/test/tools/obj2yaml/dynamic-section.test
index d8fb7e9928c..28066dd16ad 100644
--- a/test/tools/obj2yaml/dynamic-section.test
+++ b/test/tools/obj2yaml/dynamic-section.test
@@ -122,6 +122,8 @@
 # CHECK-NEXT:        Value:           0x0000000000000035
 # CHECK-NEXT:      - Tag:             DT_VERNEEDNUM
 # CHECK-NEXT:        Value:           0x0000000000000036
+# CHECK-NEXT:      - Tag:             DT_USED
+# CHECK-NEXT:        Value:           0x0000000000000001
 
 !ELF
 FileHeader:
@@ -246,3 +248,5 @@ Sections:
         Value:           0x0000000000000035
       - Tag:             DT_VERNEEDNUM
         Value:           0x0000000000000036
+      - Tag:             DT_USED
+        Value:           0x0000000000000001
-- 
2.40.0