[lld] r307013 - [LLD][LinkerScript] Allow non-alloc sections to be assigned to segments.

[Andrew Ng via llvm-commits]

Author: anng
Date: Mon Jul  3 03:11:25 2017
New Revision: 307013

URL: http://llvm.org/viewvc/llvm-project?rev=307013&view=rev
Log:
[LLD][LinkerScript] Allow non-alloc sections to be assigned to segments.

This patch makes changes to allow sections without the SHF_ALLOC bit to be
assigned to segments in a linker script.

The assignment of output sections to segments is performed in
LinkerScript::createPhdrs. Previously, this function would bail as soon as it
encountered an output section which did not have the SHF_ALLOC bit set, thus
preventing any output section without SHF_ALLOC from being assigned to a
segment.

This restriction has now been removed from LinkerScript::createPhdrs and instead
a check for SHF_ALLOC has been added to LinkerScript::adjustSectionsAfterSorting
to not propagate program headers to sections without SHF_ALLOC which matches the
behaviour of bfd linker scripts.

Differential Revision: https://reviews.llvm.org/D34204

Added:
    lld/trunk/test/ELF/linkerscript/non-alloc-segment.s
Modified:
    lld/trunk/ELF/LinkerScript.cpp

Modified: lld/trunk/ELF/LinkerScript.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LinkerScript.cpp?rev=307013&r1=307012&r2=307013&view=diff
==============================================================================
--- lld/trunk/ELF/LinkerScript.cpp (original)
+++ lld/trunk/ELF/LinkerScript.cpp Mon Jul  3 03:11:25 2017
@@ -746,10 +746,15 @@ void LinkerScript::adjustSectionsAfterSo
     if (!Cmd)
       continue;
 
-    if (Cmd->Phdrs.empty())
-      Cmd->Phdrs = DefPhdrs;
-    else
+    if (Cmd->Phdrs.empty()) {
+      OutputSection *Sec = Cmd->Sec;
+      // To match the bfd linker script behaviour, only propagate program
+      // headers to sections that are allocated.
+      if (Sec && (Sec->Flags & SHF_ALLOC))
+        Cmd->Phdrs = DefPhdrs;
+    } else {
       DefPhdrs = Cmd->Phdrs;
+    }
   }
 
   removeEmptyCommands();
@@ -880,8 +885,6 @@ std::vector<PhdrEntry> LinkerScript::cre
   // Add output sections to program headers.
   for (OutputSectionCommand *Cmd : OutputSectionCommands) {
     OutputSection *Sec = Cmd->Sec;
-    if (!(Sec->Flags & SHF_ALLOC))
-      break;
 
     // Assign headers specified by linker script
     for (size_t Id : getPhdrIndices(Sec)) {

Added: lld/trunk/test/ELF/linkerscript/non-alloc-segment.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/linkerscript/non-alloc-segment.s?rev=307013&view=auto
==============================================================================
--- lld/trunk/test/ELF/linkerscript/non-alloc-segment.s (added)
+++ lld/trunk/test/ELF/linkerscript/non-alloc-segment.s Mon Jul  3 03:11:25 2017
@@ -0,0 +1,44 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+
+################################################################################
+## Test that non-alloc section .foo can be assigned to a segment. Check that
+## the values of the offset and file size of this segment's PHDR are correct.
+##
+## This functionality allows non-alloc metadata, which is not required at
+## run-time, to be added to a custom segment in a file. This metadata may be
+## read/edited by tools/loader using the values of the offset and file size from
+## the custom segment's PHDR. This is particularly important if section headers
+## have been stripped.
+# RUN: echo "PHDRS {text PT_LOAD; foo 0x12345678;} \
+# RUN:       SECTIONS { \
+# RUN:           .text : {*(.text .text*)} :text \
+# RUN:           .foo : {*(.foo)} :foo \
+# RUN:       }" > %t.script
+# RUN: ld.lld -o %t --script %t.script %t.o
+# RUN: llvm-readobj -elf-output-style=GNU -s -l %t | FileCheck %s
+# RUN: llvm-readobj -l %t | FileCheck --check-prefix=PHDR %s
+
+# CHECK: Program Headers:
+# CHECK-NEXT:  Type
+# CHECK-NEXT:  LOAD
+# CHECK-NEXT:  <unknown>: 0x12345678
+
+# CHECK:      Section to Segment mapping:
+# CHECK-NEXT:  Segment Sections...
+# CHECK-NEXT:   00     .text
+# CHECK-NEXT:   01     .foo
+
+# PHDR: Type:  (0x12345678)
+# PHDR-NEXT: Offset: 0x1004
+# PHDR-NEXT: VirtualAddress
+# PHDR-NEXT: PhysicalAddress
+# PHDR-NEXT: FileSize: 4
+
+.global _start
+_start:
+ nop
+
+.section .foo
+ .align 4
+ .long 0