[ELF] Support . and $ in symbol names in expressions

[MaskRay]

Summary

GNU ld supports . and $ in symbol names while LLD doesn't support them in
readPrimary expressions. Using . can result in such an error:

https://github.com/ClangBuiltLinux/linux/issues/1318
ld.lld: error: ./arch/powerpc/kernel/vmlinux.lds:255: malformed number: .TOC.
>>>   __toc_ptr = (DEFINED (.TOC.) ? .TOC. : ADDR (.got)) + 0x8000;

Allow . (ppc64 special symbol .TOC.) and $ (RISC-V special symbol __global_pointer$).

Change diag[3-5].test to use an invalid character ^.

Note: GNU ld allows ~ in non-leading positions of a symbol name. ~
is not used in practice, conflicts with the unary operator, and can
cause some parsing difficulty, so this patch does not add it.

[peter.smith]

Noticed that ld.bfd will also accept ~ which may be worth adding as well; other than that looks reasonable to me.

lld/ELF/ScriptParser.cpp

1239

Looks like ld will also accept a '~' at least in some places, for example:

tem~p = 0x1000;
SECTIONS {
  boom tem~p : { *(.temp) }
}

Unlikely this will come up in practice but maybe worth matching it as well.

[MaskRay]

In D98306#2616116, @peter.smith wrote:

Noticed that ld.bfd will also accept ~ which may be worth adding as well; other than that looks reasonable to me.

We could support ~ in non-leading positions in a symbol name but that would just add unneeded complexity.

~ is also a valid unary operator so supporting it requires us to tokenize ~. A simple try

--- a/lld/ELF/ScriptLexer.cpp
+++ b/lld/ELF/ScriptLexer.cpp
@@ -174,3 +174,3 @@ bool ScriptLexer::atEOF() { return errorCount() || tokens.size() == pos; }
 static std::vector<StringRef> tokenizeExpr(StringRef s) {
-  StringRef ops = "+-*/:!~=<>"; // List of operators
+  StringRef ops = "+-*/:!=<>"; // List of operators
 
diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
index 4b15a71f029b..0b10d3a67754 100644
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -1236,2 +1236,9 @@ static void checkIfExists(OutputSection *cmd, StringRef location) {
 
+static bool isValidSymbolName(StringRef s) {
+  auto valid = [](char c) {
+    return isAlnum(c) || c == '$' || c == '.' || c == '_' || c == '~';
+  };
+  return !s.empty() && !isDigit(s[0]) && s[0] != '~' && llvm::all_of(s, valid);
+}
+
 Expr ScriptParser::readPrimary() {

does not work because symbol5 = symbol - ~0xfffb; in symbol-assignexpr.s will fail to parse.
The reason is that tokenizeExpr needs to recognize that the leading ~ in ~0xfffb can still be parsed.

Put these things together, I think ~ causes some ambiguity. Since no practical symbol names use ~, I incline to not support it.

[peter.smith]

Fair enough, I think '$' and '.' are the important ones. LGTM.

[jhenderson]

lld/ELF/ScriptParser.cpp

1419

Idle thought I had whislt taking a quick look at this change: this error message doesn't seem particularly suitable to me. There's no guarantee that the user was trying to write a number. It could easily be they wanted a symbol name.

[MaskRay]

lld/ELF/ScriptParser.cpp

1419

I noticed the same while touching this line but thought this should be a separate change.

lld/ELF/ScriptParser.cpp

StringRef ScriptParser::readParenLiteral() {
   return tok;
 }
 
 static void checkIfExists(OutputSection *cmd, StringRef location) {
   if (cmd->location.empty() && script->errorOnMissingSection)
     error(location + ": undefined section " + cmd->name);
 }
 
+static bool isValidSymbolName(StringRef s) {
+  auto valid = [](char c) {
+    return isAlnum(c) || c == '$' || c == '.' || c == '_';
+  };
+  return !s.empty() && !isDigit(s[0]) && llvm::all_of(s, valid);
+}
+
 Expr ScriptParser::readPrimary() {
   if (peek() == "(")
     return readParenExpr();
 
   if (consume("~")) {
     Expr e = readPrimary();
     return [=] { return ~e().getValue(); };
   }
Expr ScriptParser::readPrimary() {
   if (tok == ".")
     return [=] { return script->getSymbolValue(tok, location); };
 
   // Tok is a literal number.
   if (Optional<uint64_t> val = parseInt(tok))
     return [=] { return *val; };
 
   // Tok is a symbol name.
-  if (!isValidCIdentifier(tok))
+  if (!isValidSymbolName(tok))
     setError("malformed number: " + tok);
   script->referencedSymbols.push_back(tok);
   return [=] { return script->getSymbolValue(tok, location); };
 }
 
 Expr ScriptParser::readTernary(Expr cond) {
   Expr l = readExpr();
   expect(":");
   Expr r = readExpr();

lld/test/ELF/linkerscript/diag3.test

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux /dev/null -o %t.o
 # RUN: not ld.lld -shared %t.o -o /dev/null --script %s 2>&1 | FileCheck -strict-whitespace %s
 
 SECTIONS {
   .text : { *(.text) }
   .keep : { *(.keep) }
-  boom .temp : { *(.temp) }
+  boom ^temp : { *(.temp) }
 }
 
-# CHECK:      8: malformed number: .temp
-# CHECK-NEXT: >>>   boom .temp : { *(.temp) }
+# CHECK:      8: malformed number: ^temp
+# CHECK-NEXT: >>>   boom ^temp : { *(.temp) }
 # CHECK-NEXT: >>>        ^

lld/test/ELF/linkerscript/diag4.test

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux /dev/null -o %t.o
 # RUN: echo "INCLUDE \"%s\"" > %t.script
 # RUN: not ld.lld -shared %t.o -o /dev/null --script %t.script 2>&1 | FileCheck -strict-whitespace %s
 
 SECTIONS {
   .text : { *(.text) }
   .keep : { *(.keep) }
-  boom .temp : { *(.temp) }
+  boom ^temp : { *(.temp) }
 }
 
-# CHECK:      9: malformed number: .temp
-# CHECK-NEXT: >>>   boom .temp : { *(.temp) }
-# CHECK-NEXT: >>>        ^
+# CHECK:      9: malformed number: ^temp
+# CHECK-NEXT: >>>   boom ^temp : { *(.temp) }
+# CHECK-NEXT: >>>        ^
 

lld/test/ELF/linkerscript/diag5.test

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux /dev/null -o %t.o
 # RUN: echo "INCLUDE \"%s\"" > %t.script
 # RUN: not ld.lld -shared %t.o -o /dev/null --script %t.script 2>&1 | FileCheck -strict-whitespace %s
 
 SECTIONS {
   .text : { *(.text) }
   .keep : { *(.keep) }
-  boom .temp : { *(.temp) }
+  boom ^temp : { *(.temp) }
 }
 
-# CHECK:      9: malformed number: .temp
-# CHECK-NEXT: >>>   boom .temp : { *(.temp) }
+# CHECK:      9: malformed number: ^temp
+# CHECK-NEXT: >>>   boom ^temp : { *(.temp) }
 # CHECK-NEXT: >>>        ^

lld/test/ELF/linkerscript/symbol-name.test

+# REQUIRES: x86
+## Test that . and $ can be used by symbol names in expressions.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 /dev/null -o %t.o
+# RUN: ld.lld -T %s %t.o -o /dev/null
+
+a0 = DEFINED(.TOC.) ? .TOC. : 0;
+a1 = DEFINED(__global_pointer$) ? __global_pointer$ : 0;