[PATCH] D40025: [LLD] [COFF] Always truncate the .eh_frame section name

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo created this revision.

When writing a long section name, the actual section name gets written into the string table, which isn't loaded/mapped at runtime. This means that libunwind can't find the section by iterating over sections but would have to resort to static registration of .eh_frame sections.

Therefore, prefer truncation over using a long section name for .eh_frame when targeting MinGW.

This relates to the issue discussed in https://reviews.llvm.org/D39918.


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
@@ -2,9 +2,17 @@
 # RUN: lld-link /debug /out:%t.exe /entry:main %t.obj
 # RUN: llvm-readobj -sections %t.exe | FileCheck %s
 
+# RUN: lld-link /lldmingw /debug /out:%t.exe /entry:main %t.obj
+# RUN: llvm-readobj -sections %t.exe | FileCheck -check-prefix=MINGW %s
+
 # CHECK: Name: .data_long_section_name
+# CHECK: Name: .eh_frame
 # CHECK: Name: .text_long_section_name
 
+# MINGW: Name: .data_long_section_name
+# MINGW: Name: .eh_fram (
+# MINGW: Name: .text_long_section_name
+
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_AMD64
@@ -18,6 +26,10 @@
     Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
     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"
 symbols:
   - Name:            "@comp.id"
     Value:           10394907
@@ -49,6 +61,18 @@
       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
@@ -210,7 +210,8 @@
     // 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 == ".eh_frame" && Config->MinGW)) ||
+           Name.size() <= COFF::NameSize);
     strncpy(Hdr->Name, Name.data(),
             std::min(Name.size(), (size_t)COFF::NameSize));
   }
@@ -540,6 +541,8 @@
     StringRef Name = Sec->getName();
     if (Name.size() <= COFF::NameSize)
       continue;
+    if (Name == ".eh_frame" && Config->MinGW)
+      continue;
     Sec->setStringTableOff(addEntryToStringTable(Name));
   }
 


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