[ELF] - Do not crash when linkerscript applies fill to .bss.

I found that during visual inspection of code while wrote different patch.
Script in testcase probably have nothing common with real life, but
we segfault currently using it.

If output section is known NOBITS, there is no need to create
writers threads for doing nothing or proccess any filler logic that 
is useless here. We can just early return, that is what this patch do.

DIfferential revision: https://reviews.llvm.org/D33646

llvm-svn: 304192

2 files changed, 10 insertions, 0 deletions

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 7c4bf3aaebb..99c464e3714 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -1080,6 +1080,9 @@ template <class ELFT> void OutputSectionCommand::writeTo(uint8_t *Buf) {
     return;
   }
 
+  if (Sec->Type == SHT_NOBITS)
+    return;
+
   // Write leading padding.
   ArrayRef<InputSection *> Sections = Sec->Sections;
   uint32_t Filler = getFiller();
diff --git a/lld/test/ELF/linkerscript/bss-fill.s b/lld/test/ELF/linkerscript/bss-fill.s
new file mode 100644
index 00000000000..92f9fdf5619
--- /dev/null
+++ b/lld/test/ELF/linkerscript/bss-fill.s
@@ -0,0 +1,7 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS { .bss : { . += 0x10000; *(.bss) } =0xFF };" > %t.script
+# RUN: ld.lld -o %t --script %t.script %t.o
+
+.section .bss,"",@nobits
+.short 0