lld/test/MachO/local-alias-to-weak.s

   1 # REQUIRES: x86
   2 ## This test checks that when we coalesce weak definitions, their local symbol
   3 ## aliases defs don't cause the coalesced data to be retained. This was
   4 ## motivated by MC's aarch64 backend which automatically creates `ltmp<N>`
   5 ## symbols at the start of each .text section. These symbols are frequently
   6 ## aliases of other symbols created by clang or other inputs to MC. I've chosen
   7 ## to explicitly create them here since we can then reference those symbols for
   8 ## a more complete test.
   9 ##
  10 ## Not retaining the data matters for more than just size -- we have a use case
  11 ## that depends on proper data coalescing to emit a valid file format. We also
  12 ## need this behavior to properly deduplicate the __objc_protolist section;
  13 ## failure to do this can result in dyld crashing on iOS 13.
  14 ##
  15 ## Finally, ld64 does all this regardless of whether .subsections_via_symbols is
  16 ## specified. We don't. But again, given how rare the lack of that directive is
  17 ## (I've only seen it from hand-written assembly inputs), I don't think we need
  18 ## to worry about it.
  19
  20 # RUN: rm -rf %t; split-file %s %t
  21 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/weak-then-local.s -o %t/weak-then-local.o
  22 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/local-then-weak.s -o %t/local-then-weak.o
  23 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/no-subsections.s -o %t/no-subsections.o
  24 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/no-dead-strip.s -o %t/no-dead-strip.o
  25
  26 # RUN: %lld -lSystem -dylib %t/weak-then-local.o %t/local-then-weak.o -o %t/test1
  27 # RUN: llvm-objdump --macho --syms --section="__DATA,__data" --weak-bind %t/test1 | FileCheck %s
  28 # RUN: %lld -lSystem -dylib %t/local-then-weak.o %t/weak-then-local.o -o %t/test2
  29 # RUN: llvm-objdump --macho --syms --section="__DATA,__data" --weak-bind %t/test2 | FileCheck %s
  30
  31 ## Check that we only have one copy of 0x123 in the data, not two.
  32 # CHECK:       Contents of (__DATA,__data) section
  33 # CHECK-NEXT:  0000000000001000  23 01 00 00 00 00 00 00 00 10 00 00 00 00 00 00 {{$}}
  34 # CHECK-NEXT:  0000000000001010  00 10 00 00 00 00 00 00 {{$}}
  35 # CHECK-EMPTY:
  36 # CHECK-NEXT:  SYMBOL TABLE:
  37 # CHECK-NEXT:  0000000000001000 l     O __DATA,__data _alias
  38 # CHECK-NEXT:  0000000000001008 l     O __DATA,__data _ref
  39 # CHECK-NEXT:  0000000000001000 l     O __DATA,__data _alias
  40 # CHECK-NEXT:  0000000000001010 l     O __DATA,__data _ref
  41 # CHECK-NEXT:  0000000000001000  w    O __DATA,__data _weak
  42 # CHECK-NEXT:  0000000000000000         *UND* dyld_stub_binder
  43 # CHECK-EMPTY:
  44 ## Even though the references were to the non-weak `_alias` symbols, ld64 still
  45 ## emits weak binds as if they were the `_weak` symbol itself. We do not. I
  46 ## don't know of any programs that rely on this behavior, so I'm just
  47 ## documenting it here.
  48 # CHECK-NEXT:  Weak bind table:
  49 # CHECK-NEXT:  segment  section            address     type       addend   symbol
  50 # CHECK-EMPTY:
  51
  52 # RUN: %lld -lSystem -dylib %t/local-then-weak.o %t/no-subsections.o -o %t/sub-nosub
  53 # RUN: llvm-objdump --macho --syms --section="__DATA,__data" %t/sub-nosub | FileCheck %s --check-prefix SUB-NOSUB
  54
  55 ## This test case demonstrates a shortcoming of LLD: If .subsections_via_symbols
  56 ## isn't enabled, we don't elide the contents of coalesced weak symbols if they
  57 ## are part of a section that has other non-coalesced symbols. In contrast, LD64
  58 ## does elide the contents.
  59 # SUB-NOSUB:       Contents of (__DATA,__data) section
  60 # SUB-NOSUB-NEXT:  0000000000001000    23 01 00 00 00 00 00 00 00 10 00 00 00 00 00 00
  61 # SUB-NOSUB-NEXT:  0000000000001010    00 00 00 00 00 00 00 00 23 01 00 00 00 00 00 00
  62 # SUB-NOSUB-EMPTY:
  63 # SUB-NOSUB-NEXT:  SYMBOL TABLE:
  64 # SUB-NOSUB-NEXT:  0000000000001000 l     O __DATA,__data _alias
  65 # SUB-NOSUB-NEXT:  0000000000001008 l     O __DATA,__data _ref
  66 # SUB-NOSUB-NEXT:  0000000000001010 l     O __DATA,__data _zeros
  67 # SUB-NOSUB-NEXT:  0000000000001000 l     O __DATA,__data _alias
  68 # SUB-NOSUB-NEXT:  0000000000001000  w    O __DATA,__data _weak
  69 # SUB-NOSUB-NEXT:  0000000000000000         *UND* dyld_stub_binder
  70
  71 # RUN: %lld -lSystem -dylib %t/no-subsections.o %t/local-then-weak.o -o %t/nosub-sub
  72 # RUN: llvm-objdump --macho --syms --section="__DATA,__data" %t/nosub-sub | FileCheck %s --check-prefix NOSUB-SUB
  73
  74 # NOSUB-SUB:       Contents of (__DATA,__data) section
  75 # NOSUB-SUB-NEXT:  0000000000001000    00 00 00 00 00 00 00 00 23 01 00 00 00 00 00 00
  76 # NOSUB-SUB-NEXT:  0000000000001010    08 10 00 00 00 00 00 00 {{$}}
  77 # NOSUB-SUB-EMPTY:
  78 # NOSUB-SUB-NEXT:  SYMBOL TABLE:
  79 # NOSUB-SUB-NEXT:  0000000000001000 l     O __DATA,__data _zeros
  80 # NOSUB-SUB-NEXT:  0000000000001008 l     O __DATA,__data _alias
  81 # NOSUB-SUB-NEXT:  0000000000001008 l     O __DATA,__data _alias
  82 # NOSUB-SUB-NEXT:  0000000000001010 l     O __DATA,__data _ref
  83 # NOSUB-SUB-NEXT:  0000000000001008  w    O __DATA,__data _weak
  84 # NOSUB-SUB-NEXT:  0000000000000000         *UND* dyld_stub_binder
  85
  86 ## Verify that we don't drop any flags that the aliases have (such as
  87 ## .no_dead_strip). This is a regression test. We previously had subsections
  88 ## that were mistakenly stripped.
  89
  90 # RUN: %lld -lSystem -dead_strip %t/no-dead-strip.o -o %t/no-dead-strip
  91 # RUN: llvm-objdump --macho --section-headers %t/no-dead-strip | FileCheck %s \
  92 # RUN:   --check-prefix=NO-DEAD-STRIP
  93 # NO-DEAD-STRIP: __data        00000010
  94
  95 #--- weak-then-local.s
  96 .globl _weak
  97 .weak_definition _weak
  98 .data
  99 _weak:
 100 _alias:
 101   .quad 0x123
 102
 103 _ref:
 104   .quad _alias
 105
 106 .subsections_via_symbols
 107
 108 #--- local-then-weak.s
 109 .globl _weak
 110 .weak_definition _weak
 111 .data
 112 _alias:
 113 _weak:
 114   .quad 0x123
 115
 116 _ref:
 117   .quad _alias
 118
 119 .subsections_via_symbols
 120
 121 #--- no-subsections.s
 122 .globl _weak
 123 .weak_definition _weak
 124 .data
 125 _zeros:
 126 .space 8
 127
 128 _weak:
 129 _alias:
 130   .quad 0x123
 131
 132 #--- no-dead-strip.s
 133 .globl _main
 134
 135 _main:
 136   ret
 137
 138 .data
 139 .no_dead_strip l_foo, l_bar
 140
 141 _foo:
 142 l_foo:
 143   .quad 0x123
 144
 145 l_bar:
 146 _bar:
 147   .quad 0x123
 148
 149 .subsections_via_symbols