[PATCH] D79289: [LLD][ELF][ARM] Do not create .ARM.exidx sections for out of range inputs

[Peter Smith via Phabricator via llvm-commits]

psmith updated this revision to Diff 261800.
psmith added a comment.

Applied previous review comments. Added missing REQUIRES, added CHECK-NOT and simplified range checking code.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79289/new/

https://reviews.llvm.org/D79289

Files:
  lld/ELF/SyntheticSections.cpp
  lld/test/ELF/arm-exidx-range.s


Index: lld/test/ELF/arm-exidx-range.s
===================================================================
--- /dev/null
+++ lld/test/ELF/arm-exidx-range.s
@@ -0,0 +1,35 @@
+// REQUIRES: arm
+// RUN: llvm-mc --arm-add-build-attributes --triple=armv7a-linux-gnueabihf -filetype=obj %s -o %t.o
+// RUN: echo "SECTIONS { \
+// RUN:         . = 0x80000000; \
+// RUN:         .text : { *(.text) } \
+// RUN:         .vectors 0xffff0000 : { *(.vectors) } \
+// RUN: } " > %t.script
+// RUN: ld.lld --script %t.script %t.o -o %t
+// RUN: llvm-readobj -x .ARM.exidx %t | FileCheck %s
+/// Adapted from Linux kernel linker script failing due to out of range
+/// relocation. The .vectors at 0xffff0000 is a common occurrence as the vector
+/// table can only be placed at either 0 or 0xffff0000 in older ARM CPUs.
+/// In the example the .vectors won't have an exception table so if LLD creates
+/// one then we'll get a relocation out of range error. Check that we don't
+/// synthesise a table entry or place a sentinel out of range.
+
+/// Expect only .ARM.exidx from _start and sentinel
+// CHECK: Hex dump of section '.ARM.exidx':
+// CHECK-NEXT: 0x80000000 10000000 01000000 0c000000 01000000
+// CHECK-NOT:  0x80000010
+
+ .text
+ .global _start
+ .type _start, %function
+_start:
+ .fnstart
+ bx lr
+ .cantunwind
+ .fnend
+
+ .section .vectors, "ax", %progbits
+ .global vecs
+ .type vecs, %function
+vecs:
+ bx lr
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -3363,8 +3363,19 @@
   // ICF may remove executable InputSections and their dependent .ARM.exidx
   // section that we recorded earlier.
   auto isDiscarded = [](const InputSection *isec) { return !isec->isLive(); };
-  llvm::erase_if(executableSections, isDiscarded);
   llvm::erase_if(exidxSections, isDiscarded);
+  // We need to remove discarded InputSections and InputSections without
+  // .ARM.exidx sections that if we generated the .ARM.exidx it would be out
+  // of range.
+  auto isDiscardedOrOutOfRange = [this](InputSection *isec) {
+    if (!isec->isLive())
+      return true;
+    if (findExidxSection(isec))
+      return false;
+    int64_t off = static_cast<int64_t>(isec->getVA() - getVA());
+    return off != llvm::SignExtend64(off, 31);
+  };
+  llvm::erase_if(executableSections, isDiscardedOrOutOfRange);
 
   // Sort the executable sections that may or may not have associated
   // .ARM.exidx sections by order of ascending address. This requires the


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D79289.261800.patch
Type: text/x-patch
Size: 2569 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200504/04bf8b2c/attachment.bin>