[PATCH] D32397: [LLD] Avoid empty .eh_frame sections

[Mark Kettenis via Phabricator via llvm-commits]

kettenis created this revision.

Since D30335: [LLD] Add terminator to .eh_frame sections <https://reviews.llvm.org/D30335> got reverted, here is a new attempt to address the issue that prompted me to look into the unterminated .eh_frame section issue. This is that strip on OpenBSD does not correctly handle an empty .eh_frame section and produces broken binaries in that case.  Currently lld creates such an empty .eh_frame section, despite the fact that the OpenBSD crtend.o explicitly inserts a terminator.  The Linux LSB "standard":

https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html#EHFRAME

explicitly says that

>   The .eh_frame section shall contain 1 or more Call Frame Information (CFI) records.

This diff includes a test that specifically tests the issue I'm seeing on OpenBSD.


https://reviews.llvm.org/D32397

Files:
  lld/ELF/SyntheticSections.cpp
  lld/test/ELF/Inputs/eh-frame-end.s
  lld/test/ELF/eh-frame-begin-end.s


Index: lld/test/ELF/eh-frame-begin-end.s
===================================================================
--- lld/test/ELF/eh-frame-begin-end.s
+++ lld/test/ELF/eh-frame-begin-end.s
@@ -0,0 +1,17 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=amd64-unknown-openbsd %s -o %t.o
+// RUN: llvm-mc -filetype=obj -triple=amd64-unknown-openbsd %p/Inputs/eh-frame-end.s -o %t2.o
+// RUN: ld.lld %t.o %t2.o -o %t
+// RUN: llvm-readobj -sections %t | FileCheck %s
+	
+// CHECK:      Name: .eh_frame
+// CHECK-NEXT: Type: SHT_PROGBITS
+// CHECK-NEXT: Flags [
+// CHECK-NEXT:   SHF_ALLOC
+// CHECK-NEXT: ]
+// CHECK-NEXT: Address: 0x200120
+// CHECK-NEXT: Offset: 0x120
+// CHECK-NEXT: Size: 4
+
+	.section ".eh_frame", "a", @progbits
+__EH_FRAME_BEGIN__:
Index: lld/test/ELF/Inputs/eh-frame-end.s
===================================================================
--- lld/test/ELF/Inputs/eh-frame-end.s
+++ lld/test/ELF/Inputs/eh-frame-end.s
@@ -0,0 +1,2 @@
+	.section ".eh_frame", "a", @progbits
+	.long 0
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -541,6 +541,13 @@
       Off += alignTo(Fde->size(), Config->Wordsize);
     }
   }
+
+  // The LSB standard does not allow a .eh_frame section with zero
+  // Call Frame Information records. Therefore add a CIE record length
+  // 0 as a terminator if this .eh_frame section is empty.
+  if (Off == 0)
+    Off = 4;
+
   this->Size = Off;
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D32397.96305.patch
Type: text/x-patch
Size: 1534 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170423/4a117fba/attachment.bin>