[ELF] When placing orphans, handle case when last section is dead

r315292 introduced a change that's supposed to consistently ignore
"dead" output sections when placing orphans. Unfortunately, that
change doesn't handle the special case when the orphan section is
second to last section and the last section is dead (e.g. because
it's being discarded) introducing a regression in some cases.

This change handles this case by using the same predicate when
checking the last section.

Differential Revision: https://reviews.llvm.org/D39172

llvm-svn: 316307

2 files changed, 33 insertions, 6 deletions

diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 8570a807d32..836d36a5149 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -1010,11 +1010,14 @@ findOrphanPos(std::vector<BaseCommand *>::iterator B,
         Sec->SortRank < CurSec->SortRank)
       break;
   }
+
+  auto IsLiveSection = [](BaseCommand *Cmd) {
+    auto *OS = dyn_cast<OutputSection>(Cmd);
+    return OS && OS->Live;
+  };
+
   auto J = std::find_if(llvm::make_reverse_iterator(I),
-                        llvm::make_reverse_iterator(B), [](BaseCommand *Cmd) {
-                          auto *OS = dyn_cast<OutputSection>(Cmd);
-                          return OS && OS->Live;
-                        });
+                        llvm::make_reverse_iterator(B), IsLiveSection);
   I = J.base();
 
   // As a special case, if the orphan section is the last section, put
@@ -1022,8 +1025,7 @@ findOrphanPos(std::vector<BaseCommand *>::iterator B,
   // This matches bfd's behavior and is convenient when the linker script fully
   // specifies the start of the file, but doesn't care about the end (the non
   // alloc sections for example).
-  auto NextSec = std::find_if(
-      I, E, [](BaseCommand *Cmd) { return isa<OutputSection>(Cmd); });
+  auto NextSec = std::find_if(I, E, IsLiveSection);
   if (NextSec == E)
     return E;
 
diff --git a/lld/test/ELF/linkerscript/orphan-discard.s b/lld/test/ELF/linkerscript/orphan-discard.s
new file mode 100644
index 00000000000..6fd6fafcd7f
--- /dev/null
+++ b/lld/test/ELF/linkerscript/orphan-discard.s
@@ -0,0 +1,25 @@
+# REQUIRES: x86
+# RUN: llvm-mc -position-independent -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS { \
+# RUN:  . = 0xffffffff80000000; \
+# RUN:  .text : ALIGN(4096) { *(.text) } \
+# RUN:  .data : ALIGN(4096) { *(.data) } \
+# RUN:  .bss : ALIGN(4096) { *(.bss); } \
+# RUN:  . = ALIGN(4096); \
+# RUN:  _end = .; \
+# RUN:  /DISCARD/ : { *(.comment) } \
+# RUN: }" > %t.script
+# RUN: ld.lld -o %t --script %t.script %t.o
+# RUN: llvm-readelf -s -symbols %t | FileCheck %s
+
+# CHECK: .bss NOBITS ffffffff80002000 002008 000002 00 WA 0 0 4096
+# CHECK: ffffffff80003000 0 NOTYPE GLOBAL DEFAULT 3 _end
+
+.section .text, "ax"
+  ret
+
+.section .data, "aw"
+  .quad 0
+
+.section .bss, "", @nobits
+  .short 0