[PATCH] D23447: [ELF] - Do not use mergeable sections when LS is used.

[George Rimar via llvm-commits]

grimar created this revision.
grimar added a reviewer: ruiu.
grimar added subscribers: llvm-commits, grimar, evgeny777, davide.
Herald added a subscriber: emaste.

After latest changes we combine input sections with different attributes into
single output section. 
Problem here is that regular output sections does not
support adding mergeable input sections (and vise versa).
Patch just disables merging for now at the same way we do for -O0 for example.

This change helps for linking FreeBSD kernel.

https://reviews.llvm.org/D23447

Files:
  ELF/InputFiles.cpp
  test/ELF/linkerscript/linkerscript-merge-sections.s

Index: test/ELF/linkerscript/linkerscript-merge-sections.s
===================================================================
--- test/ELF/linkerscript/linkerscript-merge-sections.s
+++ test/ELF/linkerscript/linkerscript-merge-sections.s
@@ -0,0 +1,28 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS { .foo : { *(.foo.*) } }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -s %t1 | FileCheck %s
+# CHECK:      Contents of section .foo:
+# CHECK-NEXT:  0158 01000000 02000000 00000000 73686f72  ............shor
+# CHECK-NEXT:  0168 7420756e 7369676e 65642069 6e7400    t unsigned int.
+
+.global _start
+_start:
+  nop
+
+.section .foo.1, "aw"
+writable:
+ .long 1
+
+.section .foo.2, "aM", at progbits,1
+readable:
+ .long 2
+
+.section .foo.3, "awx"
+ .long 0
+
+.section .foo.4,"MS", at progbits,1
+.LASF2:
+ .string "short unsigned int"
Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -11,6 +11,7 @@
 #include "Driver.h"
 #include "Error.h"
 #include "InputSection.h"
+#include "LinkerScript.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "llvm/ADT/STLExtras.h"
@@ -162,6 +163,14 @@
   if (Config->Optimize == 0)
     return false;
 
+  // We don't merge if linker script has SECTIONS command. When script
+  // do layout it can merge several sections with different attributes
+  // into single output sections. We currently do not support adding
+  // mergeable input sections to regular output ones as well as adding
+  // regulat input sections to mergeable output.
+  if (ScriptConfig->HasContents)
+    return false;
+
   // A mergeable section with size 0 is useless because they don't have
   // any data to merge. A mergeable string section with size 0 can be
   // argued as invalid because it doesn't end with a null character.


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