[PATCH] D40025: [LLD] [COFF] Don't write long section names for sections that will be mapped at runtime

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo updated this revision to Diff 122985.
mstorsjo retitled this revision from "[LLD] [COFF] Always truncate the .eh_frame section name" to "[LLD] [COFF] Don't write long section names for sections that will be mapped at runtime".
mstorsjo edited the summary of this revision.
mstorsjo added a comment.
Herald added a subscriber: aprantl.

Always truncate the names of sections that will be mapped at runtime, as suggested by @rnk.


https://reviews.llvm.org/D40025

Files:
  COFF/Writer.cpp
  test/COFF/long-section-name.test


Index: test/COFF/long-section-name.test
===================================================================
--- test/COFF/long-section-name.test
+++ test/COFF/long-section-name.test
@@ -2,6 +2,7 @@
 # RUN: lld-link /debug /out:%t.exe /entry:main %t.obj
 # RUN: llvm-readobj -sections %t.exe | FileCheck %s
 
+# CHECK: Name: .eh_fram (
 # CHECK: Name: .data_long_section_name
 # CHECK: Name: .text_long_section_name
 
@@ -11,10 +12,14 @@
   Characteristics: [  ]
 sections:
   - Name:            .text_long_section_name
-    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_DISCARDABLE ]
     Alignment:       4
     SectionData:     B82A000000C3
   - Name:            .data_long_section_name
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE, IMAGE_SCN_MEM_DISCARDABLE ]
+    Alignment:       4
+    SectionData:     "00"
+  - Name:            .eh_frame
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
     Alignment:       4
     SectionData:     "00"
@@ -49,6 +54,18 @@
       NumberOfLinenumbers: 0
       CheckSum:        0
       Number:          0
+  - Name:            .eh_frame
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          0
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        0
+      Number:          0
   - Name:            main
     Value:           0
     SectionNumber:   1
Index: COFF/Writer.cpp
===================================================================
--- COFF/Writer.cpp
+++ COFF/Writer.cpp
@@ -211,7 +211,8 @@
     // If name is too long, write offset into the string table as a name.
     sprintf(Hdr->Name, "/%d", StringTableOff);
   } else {
-    assert(!Config->Debug || Name.size() <= COFF::NameSize);
+    assert(!Config->Debug || Name.size() <= COFF::NameSize ||
+           (Hdr->Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0);
     strncpy(Hdr->Name, Name.data(),
             std::min(Name.size(), (size_t)COFF::NameSize));
   }
@@ -541,6 +542,11 @@
     StringRef Name = Sec->getName();
     if (Name.size() <= COFF::NameSize)
       continue;
+    // If a section isn't discardable (i.e. will be mapped at runtime),
+    // prefer a truncated section name over a long section name in
+    // the string table that is unavailable at runtime.
+    if ((Sec->getPermissions() & IMAGE_SCN_MEM_DISCARDABLE) == 0)
+      continue;
     Sec->setStringTableOff(addEntryToStringTable(Name));
   }
 


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