[PATCH] D118530: [ELF] Update flag propagation rule to ignore discarded output sections

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: andrewng, ikudrin, peter.smith.
Herald added subscribers: arichardson, emaste.
MaskRay requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

See the updated insert-before.test for the effects: many synthetic
sections are SHF_ALLOC|SHF_WRITE. If they are discarded, we don't want
to propagate their flags to subsequent output section descriptions.

Depends on D118529 <https://reviews.llvm.org/D118529>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118530

Files:
  lld/ELF/LinkerScript.cpp
  lld/test/ELF/linkerscript/insert-before.test


Index: lld/test/ELF/linkerscript/insert-before.test
===================================================================
--- lld/test/ELF/linkerscript/insert-before.test
+++ lld/test/ELF/linkerscript/insert-before.test
@@ -29,7 +29,7 @@
 # CHECK2-NEXT:           NULL
 # CHECK2-NEXT: .foo.text PROGBITS 000000000020{{.*}} [[#%x,]] 000008 00  AX
 # CHECK2-NEXT: .text     PROGBITS [[#%x,]]           [[#%x,]] 000008 00  AX
-# CHECK2-NEXT: .byte     PROGBITS [[#%x,]]           [[#%x,]] 000001 00  WA
+# CHECK2-NEXT: .byte     PROGBITS [[#%x,]]           [[#%x,]] 000001 00  AX
 # CHECK2-NEXT: .foo.data PROGBITS [[#%x,]]           [[#%x,]] 000008 00  WA
 # CHECK2-NEXT: .data     PROGBITS [[#%x,]]           [[#%x,]] 000008 00  WA
 # CHECK2:      Type      {{.*}} Flg Align
Index: lld/ELF/LinkerScript.cpp
===================================================================
--- lld/ELF/LinkerScript.cpp
+++ lld/ELF/LinkerScript.cpp
@@ -1148,14 +1148,16 @@
       sec->alignment =
           std::max<uint32_t>(sec->alignment, sec->alignExpr().getValue());
 
-    // The input section might have been removed (if it was an empty synthetic
-    // section), but we at least know the flags.
-    if (sec->hasInputSections)
+    bool isEmpty = (getFirstInputSection(sec) == nullptr);
+    bool discardable = isEmpty && isDiscardable(*sec);
+    // If sec has at least an input section and not discarded, remember its
+    // flags to be inherited by subsequent output sections. (sec may contain
+    // just one empty synthetic section.)
+    if (sec->hasInputSections && !discardable)
       flags = sec->flags;
 
     // We do not want to keep any special flags for output section
     // in case it is empty.
-    bool isEmpty = (getFirstInputSection(sec) == nullptr);
     if (isEmpty)
       sec->flags = flags & ((sec->nonAlloc ? 0 : (uint64_t)SHF_ALLOC) |
                             SHF_WRITE | SHF_EXECINSTR);
@@ -1172,7 +1174,7 @@
     if (sec->sectionIndex != UINT32_MAX)
       maybePropagatePhdrs(*sec, defPhdrs);
 
-    if (isEmpty && isDiscardable(*sec)) {
+    if (discardable) {
       sec->markDead();
       cmd = nullptr;
     }


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D118530.404235.patch
Type: text/x-patch
Size: 2144 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220129/b58b8c55/attachment.bin>