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

[Jesse Huang via llvm-commits]

================
@@ -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);
----------------
jaidTw wrote:

My "note" here does not mean `desc`, I mean the whole (`namesz`, `descsz`, `type`, `name`, `desc`) structure.
There is a figure in your link that shows the alignment of two notes, which `desc` is absent in the first note. This means it is possible to have several nodes stacked one by another. So **"the next note entry"** could also be the starting address of the next note (which is `namesz`)

<img width="373" height="318" alt="圖片" src="https://github.com/user-attachments/assets/a5b1322a-8084-47de-94c7-6ee667e0b181" />

I believe we are safe to assume every note is well-aligned (I reviewed glibc/binutils and they also have the note alignment check), instead of using `desc` as the basis of alignment.

With you suggestions, I think we can
1. Remove the section alignment
2. Align at the beginning of the note (which this patch is doing)
3. For the trailing padding, I have no strong opinions on using `emitIntValue` or `emitValueToAlignment`

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