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

Currently, we can end up with NBuckets==0 and android loader
does not like it (PR36537).

Seems we can go with a minimal amount of changes here for simplicity
and be consistent with gold and so just always use >= 1 value for NBuckets.

Differential revision: https://reviews.llvm.org/D44422

llvm-svn: 327481
This commit is contained in:
George Rimar 2018-03-14 08:52:39 +00:00
parent 271ed6eb0d
commit 2ab9362bf5
4 changed files with 16 additions and 12 deletions
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16
lld/ELF/SyntheticSections.cpp
View File

@ -1799,15 +1799,19 @@ void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
return SS->CopyRelSec == nullptr && !SS->NeedsPltAddr;
return !S.Sym->isDefined();
});
// 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;
// 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);
for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
Symbol *B = Ent.Sym;
uint32_t Hash = hashGnu(B->getName());

4
lld/test/ELF/arm-execute-only.s
View File

@ -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

4
lld/test/ELF/dynamic-no-rosegment.s
View File

@ -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: ]

4
lld/test/ELF/gnu-hash-table.s
View File

@ -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: }