Allow .eh_frame_hdr to be placed before .eh_frame

Differential revision: https://reviews.llvm.org/D24041

llvm-svn: 280203

lld/ELF/Writer.cpp

@@ -1306,8 +1306,13 @@ template <class ELFT> void Writer<ELFT>::writeSections() {
   }
 
   for (OutputSectionBase<ELFT> *Sec : OutputSections)
-    if (Sec != Out<ELFT>::Opd)
+    if (Sec != Out<ELFT>::Opd && Sec != Out<ELFT>::EhFrameHdr)
       Sec->writeTo(Buf + Sec->getFileOff());
+
+  // The .eh_frame_hdr depends on .eh_frame section contents, therefore
+  // it should be written after .eh_frame is written.
+  if (!Out<ELFT>::EhFrame->empty() && Out<ELFT>::EhFrameHdr)
+    Out<ELFT>::EhFrameHdr->writeTo(Buf + Out<ELFT>::EhFrameHdr->getFileOff());
 }
 
 template <class ELFT> void Writer<ELFT>::writeBuildId() {

lld/test/ELF/linkerscript/linkerscript-eh-frame-hdr.s

@@ -0,0 +1,20 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "SECTIONS { \
+# RUN:          .eh_frame_hdr : {} \
+# RUN:          .eh_frame : {} \
+# RUN:       }" > %t.script
+# RUN: ld.lld -o %t1 --eh-frame-hdr --script %t.script %t
+# RUN: llvm-objdump -s -section=".eh_frame_hdr" %t1 | FileCheck %s
+
+# CHECK:      0158 011b033b 14000000 01000000 49000000
+# CHECK-NEXT: 0168 30000000
+
+.global _start
+_start:
+ nop
+
+.section .dah,"ax",@progbits
+.cfi_startproc
+ nop
+.cfi_endproc