[lld][WebAssembly] Add support for -soname

[sbc100]

Summary

This change writes the module name to the name section of the wasm
binary. We use the -soname argument to determine the name and we
default the output file basename if this option is not specified.

In the future we will likely want to embed the soname in the dylink
section too, but this the first step in supporting -soname.

[dschuff]

Do we really want to always write a module name even if the output is not a DSO?
For DSOs it makes sense since they would usually have symbols and names, but for final linked modules it seems to me that we should write one if there are any other debug names in the module, but maybe not otherwise. I don't know why someone would want a module name if it were the only name in the binary?

[sbc100]

In D158001#4590476, @dschuff wrote:

Do we really want to always write a module name even if the output is not a DSO?
For DSOs it makes sense since they would usually have symbols and names, but for final linked modules it seems to me that we should write one if there are any other debug names in the module, but maybe not otherwise. I don't know why someone would want a module name if it were the only name in the binary?

The entire name section is skipped if you link with --strip-all.. otherwise we generate a name section. I don't really think we would ever create a module without a name section unless --strip-all is passed since any function that has a name will be in the name section (so your module would have to have no exported symbols at all to avoid a name section in the absence of --strip-all).

In other words, I think there is little risk that this change will add a name section where there was not one previously.

[sbc100]

In D158001#4590476, @dschuff wrote:

Do we really want to always write a module name even if the output is not a DSO?

In general, yes I think this is useful feature. Especially in cases where the original filename might otherwise be lost to the runtime (e.g.. when using WebAssembly.instantiate rather than WebAssembly.instantiateStreaming)

For DSOs it makes sense since they would usually have symbols and names, but for final linked modules it seems to me that we should write one if there are any other debug names in the module, but maybe not otherwise. I don't know why someone would want a module name if it were the only name in the binary?

[dschuff]

Ah ok that makese sense.

[glandium]

FWIW, this patch breaks wasm2c, in the sense that it now generates different symbols for the same wasm linked with lld before and after this change, with no change in the link command line. Example: w2c_rlbox_0x5F_wasm_init_memory became w2c_0x24rlbox0x2Ewasm_0x5F_wasm_init_memory, and -soname doesn't make a difference.
Edit: one can use wasm2c's -n option to avoid using the module name that is now always provided by lld.

[sbc100]

In D158001#4593256, @glandium wrote:

FWIW, this patch breaks wasm2c, in the sense that it now generates different symbols for the same wasm linked with lld before and after this change, with no change in the link command line. Example: w2c_rlbox_0x5F_wasm_init_memory became w2c_0x24rlbox0x2Ewasm_0x5F_wasm_init_memory, and -soname doesn't make a difference.
Edit: one can use wasm2c's -n option to avoid using the module name that is now always provided by lld.

I see, yes it sounds like -n is probably the best solution.

Separately, I do wonder if wasm2c should strip the file extension when it sees rlbox.wasm as the module name. The .wasm part seem to translate to 0x2Ewasm in the function names which doesn't seem like it adds anything useful.

[sbc100]

In D158001#4593337, @sbc100 wrote:

In D158001#4593256, @glandium wrote:

FWIW, this patch breaks wasm2c, in the sense that it now generates different symbols for the same wasm linked with lld before and after this change, with no change in the link command line. Example: w2c_rlbox_0x5F_wasm_init_memory became w2c_0x24rlbox0x2Ewasm_0x5F_wasm_init_memory, and -soname doesn't make a difference.
Edit: one can use wasm2c's -n option to avoid using the module name that is now always provided by lld.

I see, yes it sounds like -n is probably the best solution.

Separately, I do wonder if wasm2c should strip the file extension when it sees rlbox.wasm as the module name. The .wasm part seem to translate to 0x2Ewasm in the function names which doesn't seem like it adds anything useful.

Also, it looks like the first 0x24 should probably not be there either.. that is the $ which wabt adds to names in the name section under some ciscumstances.

[glandium]

In D158001#4593337, @sbc100 wrote:

Separately, I do wonder if wasm2c should strip the file extension when it sees rlbox.wasm as the module name. The .wasm part seem to translate to 0x2Ewasm in the function names which doesn't seem like it adds anything useful.

It sure is interesting that "-n foo" doesn't do the same thing as the .wasm containing a module name of "foo".

[sbc100]

In D158001#4593397, @glandium wrote:

In D158001#4593337, @sbc100 wrote:

Separately, I do wonder if wasm2c should strip the file extension when it sees rlbox.wasm as the module name. The .wasm part seem to translate to 0x2Ewasm in the function names which doesn't seem like it adds anything useful.

It sure is interesting that "-n foo" doesn't do the same thing as the .wasm containing a module name of "foo".

Do you mean the 0x24 ($) that seems to get added by wasm2c?

[glandium]

In D158001#4605468, @sbc100 wrote:

Do you mean the 0x24 ($) that seems to get added by wasm2c?

Yes.

[sbc100]

In D158001#4606228, @glandium wrote:

In D158001#4605468, @sbc100 wrote:

Do you mean the 0x24 ($) that seems to get added by wasm2c?

Yes.

Thats seems fairly clearly to be a bug in wasm2c (to me anyway).

lld/test/wasm/build-id.test

.section .data.foo,"",@
         .hidden  foo
         .p2align        2
 foo:
         .int32  1
         .size   foo, 4
 
 
 # DEFAULT:      Contents of section build_id:
-# DEFAULT-NEXT: 0000 100e228e 4e2fa853 6393b43d ed1d4676
-# DEFAULT-NEXT: 0010 13 .
+# DEFAULT-NEXT: 0000 10299168 1e3c845a 3c8f80ae 2f16cc22  .).h.<.Z<.../.."
+# DEFAULT-NEXT: 0010 2d
 
 # SHA1:      Contents of section build_id:
-# SHA1-NEXT: 0000 14ad22e8 54d72438 94af85de 3c5592bd  ..".T.$8....<U..
-# SHA1-NEXT: 0010 1b5ec96f 6b                          .^.ok
+# SHA1-NEXT: 0000 145abdda 387a9bc4 e3aed3c3 3319cd37  .Z..8z......3..7
+# SHA1-NEXT: 0010 0212237c e4                          ..#|.
 
 # UUID:      Contents of section build_id:
 # UUID-NEXT: 0000 10
 
 # HEX:      Contents of section build_id:
 # HEX-NEXT:  0000 04123456 78                          ..4Vx
 
 
 # NONE-NOT: Contents of section build_id:

lld/test/wasm/map-file.s

 # CHECK-NEXT:       -       82       11 DATA
 # CHECK-NEXT:     400       83        8 .data
 # CHECK-NEXT:     400       89        8         {{.*}}{{/|\\}}map-file.s.tmp1.o:(.data.somedata)
 # CHECK-NEXT:     400       89        8                 somedata
 # CHECK-NEXT:     408       82        4 .bss
 # CHECK-NEXT:     408        0        4         {{.*}}{{/|\\}}map-file.s.tmp1.o:(.bss.somezeroes)
 # CHECK-NEXT:     408        0        4                 somezeroes
 # CHECK-NEXT:       -       93       12 CUSTOM(.debug_info)
-# CHECK-NEXT:       -       a5       50 CUSTOM(name)
+# CHECK-NEXT:       -       a5       61 CUSTOM(name)
 
 # RUN: not wasm-ld %t1.o -o /dev/null -Map=/ 2>&1 \
 # RUN:  | FileCheck -check-prefix=FAIL %s
 # FAIL: wasm-ld: error: cannot open map file /

lld/test/wasm/weak-alias.ll

 ; CHECK-NEXT:             Count:           2
 ; CHECK-NEXT:         Body:            23808080800041106B220024808080800020004181808080003602081081808080002101200041106A24808080800020010B
 ; CHECK-NEXT:       - Index:           5
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:           - Type:            I32
 ; CHECK-NEXT:             Count:           2
 ; CHECK-NEXT:         Body:            23808080800041106B220024808080800020004181808080003602081081808080002101200041106A24808080800020010B
 ; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     HeaderSecSizeEncodingLen: 2
 ; CHECK-NEXT:     Name:            name
 ; CHECK-NEXT:     FunctionNames:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Name:            _start
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Name:            direct_fn
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Name:            call_direct

lld/wasm/Config.h

struct Configuration {
   llvm::StringRef thinLTOJobs;
   bool ltoDebugPassManager;
   UnresolvedPolicy unresolvedSymbols;
   BuildIdKind buildId = BuildIdKind::None;
 
   llvm::StringRef entry;
   llvm::StringRef mapFile;
   llvm::StringRef outputFile;
+  llvm::StringRef soName;
   llvm::StringRef thinLTOCacheDir;
   llvm::StringRef whyExtract;
 
   llvm::StringSet<> allowUndefinedSymbols;
   llvm::StringSet<> exportedSymbols;
   std::vector<llvm::StringRef> requiredExports;
   llvm::SmallVector<llvm::StringRef, 0> searchPaths;
   llvm::CachePruningPolicy thinLTOCachePolicy;

lld/wasm/Driver.cpp

config->memoryExport =
         args.getLastArgValue(OPT_export_memory_with_name);
   } else if (args.hasArg(OPT_export_memory)) {
     config->memoryExport = memoryName;
   } else {
     config->memoryExport = std::optional<llvm::StringRef>();
   }
 
   config->sharedMemory = args.hasArg(OPT_shared_memory);
+  config->soName = args.getLastArgValue(OPT_soname);
   config->importTable = args.hasArg(OPT_import_table);
   config->importUndefined = args.hasArg(OPT_import_undefined);
   config->ltoo = args::getInteger(args, OPT_lto_O, 2);
   if (config->ltoo > 3)
     error("invalid optimization level for LTO: " + Twine(config->ltoo));
   unsigned ltoCgo =
       args::getInteger(args, OPT_lto_CGO, args::getCGOptLevel(config->ltoo));
   if (auto level = CodeGenOpt::getLevel(ltoCgo))

lld/wasm/Options.td

 def export_memory: FF<"export-memory">,
   HelpText<"Export the module's memory with the default name of \"memory\"">;
 def export_memory_with_name: JJ<"export-memory=">,
   HelpText<"Export the module's memory with the passed name">;
 
 def shared_memory: FF<"shared-memory">,
   HelpText<"Use shared linear memory">;
 
+defm soname: Eq<"soname", "Set the module name in the generated name section">;
+
 def import_table: FF<"import-table">,
   HelpText<"Import function table from the environment">;
 
 def initial_memory: JJ<"initial-memory=">,
   HelpText<"Initial size of the linear memory">;
 
 def max_memory: JJ<"max-memory=">,
   HelpText<"Maximum size of the linear memory">;

lld/wasm/SyntheticSections.h

 // Create the custom "name" section containing debug symbol names.
 class NameSection : public SyntheticSection {
 public:
   NameSection(ArrayRef<OutputSegment *> segments)
       : SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, "name"),
         segments(segments) {}
   bool isNeeded() const override { return !config->stripAll && numNames() > 0; }
   void writeBody() override;
-  unsigned numNames() const { return numNamedGlobals() + numNamedFunctions(); }
+  unsigned numNames() const {
+    // We always write at least one name which is the name of the
+    // module itself.
+    return 1 + numNamedGlobals() + numNamedFunctions();
+  }
   unsigned numNamedGlobals() const;
   unsigned numNamedFunctions() const;
   unsigned numNamedDataSegments() const;
 
 protected:
   ArrayRef<OutputSegment *> segments;
 };
 

lld/wasm/SyntheticSections.cpp

for (const OutputSegment *s : segments)
     if (!s->name.empty() && s->requiredInBinary())
       ++numNames;
 
   return numNames;
 }
 
 // Create the custom "name" section containing debug symbol names.
 void NameSection::writeBody() {
+  {
+    SubSection sub(WASM_NAMES_MODULE);
+    StringRef moduleName = config->soName;
+    if (config->soName.empty())
+      moduleName = llvm::sys::path::filename(config->outputFile);
+    writeStr(sub.os, moduleName, "module name");
+    sub.writeTo(bodyOutputStream);
+  }
+
   unsigned count = numNamedFunctions();
   if (count) {
     SubSection sub(WASM_NAMES_FUNCTION);
     writeUleb128(sub.os, count, "name count");
 
     // Function names appear in function index order.  As it happens
     // importedSymbols and inputFunctions are numbered in order with imported
     // functions coming first.

llvm/include/llvm/BinaryFormat/Wasm.h

 enum : uint8_t {
   WASM_FEATURE_PREFIX_USED = '+',
   WASM_FEATURE_PREFIX_REQUIRED = '=',
   WASM_FEATURE_PREFIX_DISALLOWED = '-',
 };
 
 // Kind codes used in the custom "name" section
 enum : unsigned {
+  WASM_NAMES_MODULE = 0,
   WASM_NAMES_FUNCTION = 1,
   WASM_NAMES_LOCAL = 2,
   WASM_NAMES_GLOBAL = 7,
   WASM_NAMES_DATA_SEGMENT = 9,
 };
 
 // Kind codes used in the custom "linking" section
 enum : unsigned {