[llvm] Fix MachO exports trie parsing.

[ributzka]

Summary

The exports trie parser ordinal validation check doesn't consider the case where
the ordinal can be zero or negative for certain special values that are defined
in BindSpecialDylib. Update the validation to account for that fact and add a
test case.

This fixes rdar://94844233.

[pete]

LGTM

[ributzka]

Thank you Pete

[ributzka]

OpenMP pre-merge check issues seem unrelated to this change.

llvm/lib/Object/MachOObjectFile.cpp

if (State.Flags & MachO::EXPORT_SYMBOL_FLAGS_REEXPORT) {
       if (error) {
         *E = malformedError("dylib ordinal of re-export " + Twine(error) +
                             " in export trie data at node: 0x" +
                             Twine::utohexstr(offset));
         moveToEnd();
         return;
       }
       if (O != nullptr) {
-        if (State.Other > O->getLibraryCount()) {
+        // Only positive numbers represent library ordinals. Zero and negative
+        // numbers have special meaning (see BindSpecialDylib).
+        if ((int64_t)State.Other > 0 && State.Other > O->getLibraryCount()) {
           *E = malformedError(
               "bad library ordinal: " + Twine((int)State.Other) + " (max " +
               Twine((int)O->getLibraryCount()) +
               ") in export trie data at node: 0x" + Twine::utohexstr(offset));
           moveToEnd();
           return;
         }
       }

llvm/test/Object/AArch64/nm-flat-reexport.test

+RUN: rm -rf %t && mkdir -p %t
+RUN: yaml2obj %p/../Inputs/MachO/flat-reexport.yaml -o %t/flat-reexport
+RUN: llvm-nm --dyldinfo-only %t/flat-reexport | FileCheck %s
+
+CHECK-NOT: error
+CHECK: _fputc
+CHECK: _sym1
 No newline at end of file

llvm/test/Object/Inputs/MachO/flat-reexport.yaml

+# echo "_fputc" >> reexports.exp
+# echo "void sym1(void){}" | xcrun clang --target=arm64-apple-macos11.0 -o flat-reexport -dynamiclib -Wl,-reexported_symbols_list,reexports.exp -Wl,-flat_namespace -x c -
+# obj2yaml --raw-segment=data --raw-segment=linkedit flat-reexport > flat-reexport.yaml
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x100000C
+  cpusubtype:      0x0
+  filetype:        0x6
+  ncmds:           13
+  sizeofcmds:      672
+  flags:           0x108004
+  reserved:        0x0
+LoadCommands:
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+    cmdsize:         232
+    segname:         __TEXT
+    vmaddr:          0
+    vmsize:          16384
+    fileoff:         0
+    filesize:        16384
+    maxprot:         5
+    initprot:        5
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+    flags:           0
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+        content:         C0035FD6
+      - sectname:        __unwind_info
+        segname:         __TEXT
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+        offset:          0x3FB8
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+  - cmd:             LC_SEGMENT_64
+    cmdsize:         72
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+    vmsize:          16384
+    fileoff:         16384
+    filesize:        442
+    maxprot:         1
+    initprot:        1
+    nsects:          0
+    flags:           0
+  - cmd:             LC_ID_DYLIB
+    cmdsize:         40
+    dylib:
+      name:            24
+      timestamp:       1
+      current_version: 0
+      compatibility_version: 0
+    Content:         flat-reexport
+    ZeroPadBytes:    3
+  - cmd:             LC_DYLD_INFO_ONLY
+    cmdsize:         48
+    rebase_off:      0
+    rebase_size:     0
+    bind_off:        0
+    bind_size:       0
+    weak_bind_off:   0
+    weak_bind_size:  0
+    lazy_bind_off:   0
+    lazy_bind_size:  0
+    export_off:      16384
+    export_size:     40
+  - cmd:             LC_SYMTAB
+    cmdsize:         24
+    symoff:          16432
+    nsyms:           4
+    stroff:          16496
+    strsize:         40
+  - cmd:             LC_DYSYMTAB
+    cmdsize:         80
+    ilocalsym:       0
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+    iundefsym:       2
+    nundefsym:       2
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+  - cmd:             LC_UUID
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+  - cmd:             LC_BUILD_VERSION
+    cmdsize:         32
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+    minos:           720896
+    sdk:             787712
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+    Tools:
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+        version:         53280768
+  - cmd:             LC_SOURCE_VERSION
+    cmdsize:         16
+    version:         0
+  - cmd:             LC_LOAD_DYLIB
+    cmdsize:         56
+    dylib:
+      name:            24
+      timestamp:       2
+      current_version: 85948417
+      compatibility_version: 65536
+    Content:         '/usr/lib/libSystem.B.dylib'
+    ZeroPadBytes:    6
+  - cmd:             LC_FUNCTION_STARTS
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+    datasize:        8
+  - cmd:             LC_DATA_IN_CODE
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+...