Add support for the .base64 directive (fixes #165499)

[kenballus]

Starting in version 15, GCC emits a .base64 directive instead of .string or .ascii for char arrays of length >= 3.

See this godbolt link for an example.

This patch adds support for the .base64 directive to AsmParser.cpp, so tools like llvm-mc can process the output of GCC more effectively.

This addresses #165499.

[github-actions]

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

[llvmbot]

@llvm/pr-subscribers-llvm-mc

Author: Ben Kallus (kenballus)

Changes

Starting in version 15, GCC emits a .base64 directive instead of .string or .ascii for char arrays of length >= 3.

See this godbolt link for an example.

This patch adds support for the .base64 directive to AsmParser.cpp, so tools like llvm-mc can process the output of GCC more effectively.

This addresses #165499.

---

Full diff: https://github.com/llvm/llvm-project/pull/165549.diff

1 Files Affected:

• (modified) llvm/lib/MC/MCParser/AsmParser.cpp (+21)

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index dd1bc2be5feb4..54bb1451a5a73 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -46,6 +46,7 @@
 #include "llvm/MC/MCSymbolMachO.h"
 #include "llvm/MC/MCTargetOptions.h"
 #include "llvm/MC/MCValue.h"
+#include "llvm/Support/Base64.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -530,6 +531,7 @@ class AsmParser : public MCAsmParser {
     DK_LTO_SET_CONDITIONAL,
     DK_CFI_MTE_TAGGED_FRAME,
     DK_MEMTAG,
+    DK_BASE64,
     DK_END
   };
 
@@ -552,6 +554,7 @@ class AsmParser : public MCAsmParser {
 
   // ".ascii", ".asciz", ".string"
   bool parseDirectiveAscii(StringRef IDVal, bool ZeroTerminated);
+  bool parseDirectiveBase64();                  // ".base64"
   bool parseDirectiveReloc(SMLoc DirectiveLoc); // ".reloc"
   bool parseDirectiveValue(StringRef IDVal,
                            unsigned Size);       // ".byte", ".long", ...
@@ -1953,6 +1956,8 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
     case DK_ASCIZ:
     case DK_STRING:
       return parseDirectiveAscii(IDVal, true);
+    case DK_BASE64:
+      return parseDirectiveBase64();
     case DK_BYTE:
     case DK_DC_B:
       return parseDirectiveValue(IDVal, 1);
@@ -3076,6 +3081,21 @@ bool AsmParser::parseDirectiveAscii(StringRef IDVal, bool ZeroTerminated) {
   return parseMany(parseOp);
 }
 
+/// parseDirectiveBase64:
+//    ::= .base64 "string"
+bool AsmParser::parseDirectiveBase64() {
+  std::vector<char> Decoded;
+
+  std::string str;
+
+  if (parseEscapedString(str) || str.empty() || decodeBase64(str, Decoded)) {
+    return true;
+  }
+
+  getStreamer().emitBytes(std::string(Decoded.begin(), Decoded.end()));
+  return false;
+}
+
 /// parseDirectiveReloc
 ///  ::= .reloc expression , identifier [ , expression ]
 bool AsmParser::parseDirectiveReloc(SMLoc DirectiveLoc) {
@@ -5345,6 +5365,7 @@ void AsmParser::initializeDirectiveKindMap() {
   DirectiveKindMap[".asciz"] = DK_ASCIZ;
   DirectiveKindMap[".string"] = DK_STRING;
   DirectiveKindMap[".byte"] = DK_BYTE;
+  DirectiveKindMap[".base64"] = DK_BASE64;
   DirectiveKindMap[".short"] = DK_SHORT;
   DirectiveKindMap[".value"] = DK_VALUE;
   DirectiveKindMap[".2byte"] = DK_2BYTE;

[lenary]

Please add tests.

[kenballus]

Tests added. If you'd like anything else tested, please let me know.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[lenary]

LGTM. Please wait for any more comments from Maskray before landing.

[kenballus]

One more thing to consider:

The .base64 directive from GNU as accepts a comma-separated list of strings, and decodes them all. However, GCC doesn't emit a comma-separated list for this directive, and the point of this patch is to be more compatible with GCC, not as.

If we want llvm-mc to be perfectly compatible with as, then I should probably add that functionality. If we instead only want to be compatible with GCC without complicating things too much, then this is likely fine as-is. I'll leave the decision to you all.

[lenary]

Oh. Please can you add support for multiple string arguments (to align with gnu as), as we would like portability between as-compatible code and Clang/LLVM's integrated assembler.

[kenballus]

Oh. Please can you add support for multiple string arguments (to align with gnu as), as we would like portability between as-compatible code and Clang/LLVM's integrated assembler.

Will do!

[kenballus]

Oh. Please can you add support for multiple string arguments (to align with gnu as), as we would like portability between as-compatible code and Clang/LLVM's integrated assembler.

Done.

[lenary]

You probably need to merge main into your branch to get the tests to pass, I'm not sure though. The failures are unrelated as far as I can tell.

Can you also check your code formatting again? The comment above has been re-used to show the diff for where things need to be updated.

[kenballus]

You probably need to merge main into your branch to get the tests to pass, I'm not sure though. The failures are unrelated as far as I can tell.

Can you also check your code formatting again? The comment above has been re-used to show the diff for where things need to be updated.

Got it. Now merged and reformatted.

[lenary]

LGTM. Thanks for the updates.

[lenary]

@kenballus please can you follow these instructions: https://llvm.org/docs/DeveloperPolicy.html#github-email-address (and then I will merge this PR)

[kenballus]

@kenballus please can you follow these instructions: https://llvm.org/docs/DeveloperPolicy.html#github-email-address (and then I will merge this PR)

Done.

[github-actions]

@kenballus Congratulations on having your first Pull Request (PR) merged into the LLVM Project!

Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR.

Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues.

How to do this, and the rest of the post-merge process, is covered in detail here.

If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again.

If you don't get any reports, no action is required from you. Your changes are working as expected, well done!