[PATCH] D44422: [ELF] - Never create .gnu_hash with NBuckets == 0.

[George Rimar via Phabricator via llvm-commits]

This revision was not accepted when it landed; it landed in state "Needs Review".
This revision was automatically updated to reflect the committed changes.
Closed by commit rLLD327481: [ELF] - Never create .gnu_hash with NBuckets == 0. (authored by grimar, committed by ).
Herald added a subscriber: srhines.

Changed prior to commit:
  https://reviews.llvm.org/D44422?vs=138161&id=138306#toc

Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D44422

Files:
  ELF/SyntheticSections.cpp
  test/ELF/arm-execute-only.s
  test/ELF/dynamic-no-rosegment.s
  test/ELF/gnu-hash-table.s


Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -1799,15 +1799,19 @@
           return SS->CopyRelSec == nullptr && !SS->NeedsPltAddr;
         return !S.Sym->isDefined();
       });
-  if (Mid == V.end())
-    return;
 
-  // We chose load factor 4 for the on-disk hash table. For each hash
-  // collision, the dynamic linker will compare a uint32_t hash value.
-  // Since the integer comparison is quite fast, we believe we can make
-  // the load factor even larger. 4 is just a conservative choice.
+  // Even if the hash table does not contain symbols, we still want to keep the
+  // section to indicate to a loader that the file exports no symbols. We can't
+  // have zero buckets because the android loader doesn't support that. We chose
+  // load factor 4 for the on-disk hash table. For each hash collision, the
+  // dynamic linker will compare a uint32_t hash value. Since the integer
+  // comparison is quite fast, we believe we can make the load factor even
+  // larger. 4 is just a conservative choice.
   NBuckets = std::max<size_t>((V.end() - Mid) / 4, 1);
 
+  if (Mid == V.end())
+    return;
+
   for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
     Symbol *B = Ent.Sym;
     uint32_t Hash = hashGnu(B->getName());
Index: test/ELF/arm-execute-only.s
===================================================================
--- test/ELF/arm-execute-only.s
+++ test/ELF/arm-execute-only.s
@@ -14,7 +14,7 @@
 // RUN: llvm-readelf -l %t.so | FileCheck --check-prefix=DIFF %s
 
 // CHECK-NOT:  LOAD
-// CHECK:      LOAD           0x000000 0x00000000 0x00000000 0x00169  0x00169  R   0x1000
+// CHECK:      LOAD           0x000000 0x00000000 0x00000000 0x0016d  0x0016d  R   0x1000
 // CHECK:      LOAD           0x001000 0x00001000 0x00001000 0x{{.*}} 0x{{.*}} R E 0x1000
 // CHECK:      LOAD           0x002000 0x00002000 0x00002000 0x{{.*}} 0x{{.*}}   E 0x1000
 // CHECK:      LOAD           0x003000 0x00003000 0x00003000 0x00038  0x00038  RW  0x1000
@@ -26,7 +26,7 @@
 // CHECK: 04     .dynamic
 
 // DIFF-NOT:  LOAD
-// DIFF:      LOAD           0x000000 0x00000000 0x00000000 0x00149 0x00149 R   0x1000
+// DIFF:      LOAD           0x000000 0x00000000 0x00000000 0x0014d 0x0014d R   0x1000
 // DIFF:      LOAD           0x001000 0x00001000 0x00001000 0x0000c 0x0000c R E 0x1000
 // DIFF:      LOAD           0x002000 0x00002000 0x00002000 0x00038 0x00038 RW  0x1000
 // DIFF-NOT:  LOAD
Index: test/ELF/dynamic-no-rosegment.s
===================================================================
--- test/ELF/dynamic-no-rosegment.s
+++ test/ELF/dynamic-no-rosegment.s
@@ -7,9 +7,9 @@
 # CHECK-NEXT:   Tag                Type                 Name/Value
 # CHECK-NEXT:   0x0000000000000006 SYMTAB               0x120
 # CHECK-NEXT:   0x000000000000000B SYMENT               24 (bytes)
-# CHECK-NEXT:   0x0000000000000005 STRTAB               0x1D0
+# CHECK-NEXT:   0x0000000000000005 STRTAB               0x1D8
 # CHECK-NEXT:   0x000000000000000A STRSZ                1 (bytes)
 # CHECK-NEXT:   0x000000006FFFFEF5 GNU_HASH             0x138
-# CHECK-NEXT:   0x0000000000000004 HASH                 0x150
+# CHECK-NEXT:   0x0000000000000004 HASH                 0x154
 # CHECK-NEXT:   0x0000000000000000 NULL                 0x0
 # CHECK-NEXT: ]
Index: test/ELF/gnu-hash-table.s
===================================================================
--- test/ELF/gnu-hash-table.s
+++ test/ELF/gnu-hash-table.s
@@ -51,12 +51,12 @@
 # EMPTY-NEXT:   }
 # EMPTY-NEXT: ]
 # EMPTY:      GnuHashTable {
-# EMPTY-NEXT:   Num Buckets: 0
+# EMPTY-NEXT:   Num Buckets: 1
 # EMPTY-NEXT:   First Hashed Symbol Index: 2
 # EMPTY-NEXT:   Num Mask Words: 1
 # EMPTY-NEXT:   Shift Count: 5
 # EMPTY-NEXT:   Bloom Filter: [0x0]
-# EMPTY-NEXT:   Buckets: []
+# EMPTY-NEXT:   Buckets: [0]
 # EMPTY-NEXT:   Values: []
 # EMPTY-NEXT: }
 


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