From: Fangrui Song <maskray@google.com>
Date: Sun, 29 Sep 2019 15:26:12 +0000 (+0000)
Subject: [MC] Emit unused undefined symbol even if its binding is not set
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=d2092dc525ec36d958e0aaa318e47666ed3ba3e7;p=llvm

[MC] Emit unused undefined symbol even if its binding is not set

For the following two cases, we currently suppress the symbols. This
patch emits them (compatible with GNU as).

* `test2_a = undef`: if `undef` is otherwise unused.
* `.hidden hidden`: if `hidden` is unused. This is the main point of the
  patch, because omitting the symbol would cause a linker semantic
  difference.

It causes a behavior change that is not compatible with GNU as:

.weakref foo1, bar1

When neither foo1 nor bar1 is used, we now emit bar1, which is arguably
more consistent.

Another change is that we will emit .TOC. for .TOC.@tocbase .  For this
directive, suppressing .TOC. can be seen as a size optimization, but we
choose to drop it for simplicity and consistency.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373168 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/MC/ELFObjectWriter.cpp b/lib/MC/ELFObjectWriter.cpp
index 6f160e491ce..f8e93889344 100644
--- a/lib/MC/ELFObjectWriter.cpp
+++ b/lib/MC/ELFObjectWriter.cpp
@@ -615,9 +615,6 @@ bool ELFWriter::isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
     return false;
   }
 
-  if (Symbol.isUndefined() && !Symbol.isBindingSet())
-    return false;
-
   if (Symbol.isTemporary())
     return false;
 
diff --git a/test/MC/ELF/undef.s b/test/MC/ELF/undef.s
index f313d71369e..9d99b834ffd 100644
--- a/test/MC/ELF/undef.s
+++ b/test/MC/ELF/undef.s
@@ -18,6 +18,8 @@
         .text
         movsd   .Lsym8(%rip), %xmm1
 
+.hidden hidden
+
 test2_a = undef
 test2_b = undef + 1
 
@@ -41,6 +43,17 @@ test2_b = undef + 1
 // CHECK-NEXT:     Section: .rodata.str1.1
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: hidden
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Global
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other [
+// CHECK-NEXT:       STV_HIDDEN
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Section: Undefined
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: sym6
 // CHECK-NEXT:     Value: 0x0
 // CHECK-NEXT:     Size: 0
@@ -49,4 +62,13 @@ test2_b = undef + 1
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: Undefined
 // CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: undef
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Global
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Undefined
+// CHECK-NEXT:   }
 // CHECK-NEXT: ]
diff --git a/test/MC/ELF/weakref.s b/test/MC/ELF/weakref.s
index 51905d8ad7c..bca8ec4f281 100644
--- a/test/MC/ELF/weakref.s
+++ b/test/MC/ELF/weakref.s
@@ -125,6 +125,15 @@ bar15:
 // CHECK-NEXT:     Section: .text
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name: bar1
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Global
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Undefined
+// CHECK-NEXT:   }
+// CHECK-NEXT:   Symbol {
 // CHECK-NEXT:     Name: bar10
 // CHECK-NEXT:     Value: 0x28
 // CHECK-NEXT:     Size: 0