[llvm] [RISCV] Improvements to .note.gnu.property section. (PR #151436)

[Ming-Yi Lai via llvm-commits]

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@@ -83,29 +86,21 @@ void RISCVTargetStreamer::emitNoteGnuPropertySection(
   OutStreamer.switchSection(NoteSection);
 
   // Emit the note header
-  OutStreamer.emitIntValue(4, 4); // n_namsz
-
-  MCSymbol *const NDescBeginSym = Ctx.createTempSymbol();
-  MCSymbol *const NDescEndSym = Ctx.createTempSymbol();
-  const MCExpr *const NDescSzExpr =
-      MCBinaryExpr::createSub(MCSymbolRefExpr::create(NDescEndSym, Ctx),
-                              MCSymbolRefExpr::create(NDescBeginSym, Ctx), Ctx);
-
-  OutStreamer.emitValue(NDescSzExpr, 4);                    // n_descsz
+  OutStreamer.emitValueToAlignment(NoteAlign);
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mylai-mtk wrote:

By interpreting together "Padding is present, if necessary, to ensure 8 or 4-byte alignment for the descriptor (depending on whether the file is a 64-bit or 32-bit object)." and "Padding is present, if necessary, to ensure 8 or 4-byte alignment for the next note entry (depending on whether the file is a 64-bit or 32-bit object).", it requires every `desc` (your "note", I guess) to be aligned.

And add to it the sauce of "The section alignment (in ELF, sh_addralign) is the maximum value of all alignment directives in the section.", the section will be aligned by at least 8 or 4-byte. But I feel this is more like an implication, not an explicit requirement. Consider the case where there's no `desc` elements and thus no alignment requirement is present in the section content, do we still need to align the note header? I don't know.

https://github.com/llvm/llvm-project/pull/151436