[PATCH] D123283: [MC] Improve st_size propagation rule

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 421364.
MaskRay marked 2 inline comments as done.
MaskRay edited the summary of this revision.
MaskRay added a comment.

Implement the chained lookup. Fix zatrazz's case.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123283/new/

https://reviews.llvm.org/D123283

Files:
  llvm/lib/MC/ELFObjectWriter.cpp
  llvm/test/MC/ELF/offset.s


Index: llvm/test/MC/ELF/offset.s
===================================================================
--- llvm/test/MC/ELF/offset.s
+++ llvm/test/MC/ELF/offset.s
@@ -14,15 +14,15 @@
 # CHECK-NEXT:    000000000000000d    42 OBJECT  GLOBAL DEFAULT [[#A]]  d1
 # CHECK-NEXT:    000000000000000d    42 OBJECT  GLOBAL DEFAULT [[#A]]  d2
 # CHECK-NEXT:    0000000000000001    41 OBJECT  GLOBAL DEFAULT [[#A]]  e
-# CHECK-NEXT:    0000000000000001    42 OBJECT  GLOBAL DEFAULT [[#A]]  e1
-# CHECK-NEXT:    0000000000000001    42 OBJECT  GLOBAL DEFAULT [[#A]]  e2
+# CHECK-NEXT:    0000000000000001    41 OBJECT  GLOBAL DEFAULT [[#A]]  e1
+# CHECK-NEXT:    0000000000000001    41 OBJECT  GLOBAL DEFAULT [[#A]]  e2
 # CHECK-NEXT:    0000000000000002    42 OBJECT  GLOBAL DEFAULT [[#A]]  e3
 # CHECK-NEXT:    0000000000000005     0 NOTYPE  GLOBAL DEFAULT [[#A]]  test2_a
 # CHECK-NEXT:    0000000000000005     0 NOTYPE  GLOBAL DEFAULT [[#A]]  test2_b
 # CHECK-NEXT:    0000000000000009     0 NOTYPE  GLOBAL DEFAULT [[#A]]  test2_c
 # CHECK-NEXT:    0000000000000009     0 NOTYPE  GLOBAL DEFAULT [[#A]]  test2_d
 # CHECK-NEXT:    0000000000000004     0 NOTYPE  GLOBAL DEFAULT  ABS    test2_e
-# CHECK-NEXT:    0000000000000001    42 OBJECT  GLOBAL DEFAULT [[#A]]  e at v1
+# CHECK-NEXT:    0000000000000001    41 OBJECT  GLOBAL DEFAULT [[#A]]  e at v1
 
 
         .data
@@ -45,7 +45,8 @@
 
 e = a + (1 - 1)
 .size e, 41
-## FIXME These st_size fields inherit from e instead of a.
+## These st_size fields inherit from e instead of a.
+## TODO e3's st_size should inherit from e.
 .set e1, e
 .set e2, e1
 e3 = e1 + 1
Index: llvm/lib/MC/ELFObjectWriter.cpp
===================================================================
--- llvm/lib/MC/ELFObjectWriter.cpp
+++ llvm/lib/MC/ELFObjectWriter.cpp
@@ -547,9 +547,27 @@
   uint64_t Size = 0;
 
   const MCExpr *ESize = MSD.Symbol->getSize();
-  if (!ESize && Base)
+  if (!ESize && Base) {
+    // For expressions like .set y, x+1, if y's size is unset, inherit from x.
     ESize = Base->getSize();
 
+    // For `.size x, 2; y = x; .size y, 1; z = y; z1 = z; .symver y, y at v1`, z,
+    // z1, and y at v1's st_size equals y's. However, `Base` is `x` which will give
+    // us 2. Follow the MCSymbolRefExpr assignment chain, which covers most
+    // needs. MCBinaryExpr is not handled.
+    const MCSymbolELF *Sym = &Symbol;
+    while (Sym->isVariable()) {
+      if (auto *Expr =
+              dyn_cast<MCSymbolRefExpr>(Sym->getVariableValue(false))) {
+        Sym = cast<MCSymbolELF>(&Expr->getSymbol());
+        if (!Sym->getSize())
+          continue;
+        ESize = Sym->getSize();
+      }
+      break;
+    }
+  }
+
   if (ESize) {
     int64_t Res;
     if (!ESize->evaluateKnownAbsolute(Res, Layout))


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D123283.421364.patch
Type: text/x-patch
Size: 2747 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220407/fa6d02d1/attachment.bin>