Index: lib/ObjectYAML/ELFYAML.cpp
===================================================================
--- lib/ObjectYAML/ELFYAML.cpp
+++ lib/ObjectYAML/ELFYAML.cpp
@@ -888,9 +888,25 @@
   IO.mapOptional("Binding", Symbol.Binding, ELFYAML::ELF_STB(0));
   IO.mapOptional("Value", Symbol.Value, Hex64(0));
   IO.mapOptional("Size", Symbol.Size, Hex64(0));
-  MappingNormalization<NormalizedOther, uint8_t> Keys(IO, Symbol.Other);
-  IO.mapOptional("Visibility", Keys->Visibility, ELFYAML::ELF_STV(0));
-  IO.mapOptional("Other", Keys->Other, ELFYAML::ELF_STO(0));
+
+  // Symbol's Other field is a bit special. It is a bit field that represents
+  // st_other and usually holds symbol visibility. When we write a YAML document
+  // we split it into two fields named "Visibility" and "Other". The latter one
+  // usually holds no value, and so is almost never printed, although some
+  // targets (e.g. MIPS) may use it to specify the named bits to set (e.g.
+  // STO_MIPS_OPTIONAL). For producing broken objects we want to allow writing
+  // any value to st_other. To do this we allow one more field called "StOther".
+  // If it is present in a YAML document, we set st_other to that integer,
+  // ignoring the other fields.
+  Optional<llvm::yaml::Hex64> Other;
+  IO.mapOptional("StOther", Other);
+  if (Other) {
+    Symbol.Other = *Other;
+  } else {
+    MappingNormalization<NormalizedOther, uint8_t> Keys(IO, Symbol.Other);
+    IO.mapOptional("Visibility", Keys->Visibility, ELFYAML::ELF_STV(0));
+    IO.mapOptional("Other", Keys->Other, ELFYAML::ELF_STO(0));
+  }
 }
 
 StringRef MappingTraits<ELFYAML::Symbol>::validate(IO &IO,
Index: test/tools/llvm-readobj/elf-symbol-visibility.test
===================================================================
--- test/tools/llvm-readobj/elf-symbol-visibility.test
+++ test/tools/llvm-readobj/elf-symbol-visibility.test
@@ -1,11 +1,9 @@
 # Show that llvm-readobj prints the symbol visibility where recognised, or
 # something sensible when not, for both GNU and LLVM output.
 
-# Use --dyn-symbols because it is only possible to hand-craft symbols with
-# non-standard st_other values for .dynsym.
 # RUN: yaml2obj %s > %t
-# RUN: llvm-readobj --symbols --dyn-symbols %t | FileCheck %s --check-prefix=LLVM
-# RUN: llvm-readelf --symbols --dyn-symbols %t | FileCheck %s --check-prefix=GNU
+# RUN: llvm-readobj --symbols %t | FileCheck %s --check-prefix=LLVM
+# RUN: llvm-readelf --symbols %t | FileCheck %s --check-prefix=GNU
 
 # LLVM:      Name: default
 # LLVM:      Other: 0
@@ -27,11 +25,11 @@
 
 # FIXME - the "other" symbol should print something indicating its non-zero st_other value.
 # See https://bugs.llvm.org/show_bug.cgi?id=40785.
-# GNU:      DEFAULT   {{.*}} other
 # GNU:      DEFAULT   {{.*}} default
 # GNU-NEXT: INTERNAL  {{.*}} internal
 # GNU-NEXT: HIDDEN    {{.*}} hidden
 # GNU-NEXT: PROTECTED {{.*}} protected
+# GNU-NEXT: DEFAULT   {{.*}} other
 
 !ELF
 FileHeader:
@@ -39,18 +37,6 @@
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_386
-Sections:
-  - Name: .dynstr
-    Type: SHT_STRTAB
-    #\0other\0
-    Content: "006f7468657200"
-  - Name: .dynsym
-    Type: SHT_DYNSYM
-    Link: .dynstr
-    EntSize: 16
-    # Null symbol
-    # Symbol with st_name = 1, st_other = 0x4
-    Content: "0000000000000000000000000000000001000000000000000000000000040000"
 Symbols:
   - Name: default
     Visibility: STV_DEFAULT
@@ -64,3 +50,6 @@
   - Name: protected
     Visibility: STV_PROTECTED
     Binding: STB_GLOBAL
+  - Name: other
+    Binding: STB_GLOBAL
+    StOther: 4
Index: test/tools/yaml2obj/elf-symbol-stother.yaml
===================================================================
--- /dev/null
+++ test/tools/yaml2obj/elf-symbol-stother.yaml
@@ -0,0 +1,79 @@
+## Test how yaml2obj sets the value of a symbol's st_other fields.
+
+## Show that yaml2obj reports an error when STO_* flag that belongs
+## to a different machine type to what is specified by the YAML.
+
+# RUN: not yaml2obj --docnum=1 2>&1 %s | FileCheck %s --check-prefix=ERR
+# ERR:      error: unknown bit value
+# ERR-NEXT: Other: [ STO_MIPS_OPTIONAL ]
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_386
+Symbols:
+  - Name:  foo
+    Other: [ STO_MIPS_OPTIONAL ]
+
+## Test that STO_* can be used with their correct machine type.
+## We use the same YAML as above, but with a change of machine type.
+
+# RUN: yaml2obj --docnum=2 %s > %t2
+# RUN: llvm-readobj --symbols %t2 | FileCheck %s --check-prefix=USE-OTHER
+
+# USE-OTHER:      Name: foo
+# USE-OTHER:      Other [ (0x4)
+# USE-OTHER-NEXT:   STO_MIPS_OPTIONAL (0x4)
+# USE-OTHER-NEXT: ]
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_MIPS
+Symbols:
+  - Name:  foo
+    Other: [ STO_MIPS_OPTIONAL ]
+
+## Test that instead of using the "Other" field we can use the "StOther" field
+## to set st_other to any arbitrary value.
+
+# RUN: yaml2obj --docnum=3 %s > %t3
+# RUN: llvm-readobj --symbols %t3 | FileCheck %s --check-prefix=USE-STOTHER
+# RUN: yaml2obj --docnum=4 %s > %t4
+# RUN: llvm-readobj --symbols %t4 | FileCheck %s --check-prefix=USE-STOTHER
+
+# USE-STOTHER:      Name: foo
+# USE-STOTHER:      Other [
+# USE-STOTHER-SAME: (0x4)
+
+# USE-STOTHER:      Name: bar
+# USE-STOTHER:      Other [
+# USE-STOTHER-SAME: (0xFF)
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_MIPS
+Symbols:
+  - Name:    foo
+    StOther: 4
+  - Name:    bar
+    StOther: 0xff
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_386
+Symbols:
+  - Name:    foo
+    StOther: 4
+  - Name:    bar
+    StOther: 0xff