[LLD][COFF] Move entry thunk offset writing to writeSections (NFC)

[cjacek]

To make it easier to add entry thunks to other chunk types.

[llvmbot]

@llvm/pr-subscribers-lld-coff

@llvm/pr-subscribers-lld

Author: Jacek Caban (cjacek)

Changes

To make it easier to add entry thunks to other chunk types.

---

Full diff: https://github.com/llvm/llvm-project/pull/151254.diff

2 Files Affected:

• (modified) lld/COFF/Chunks.cpp (-6)
• (modified) lld/COFF/Writer.cpp (+9-1)

diff --git a/lld/COFF/Chunks.cpp b/lld/COFF/Chunks.cpp
index 01752cdc6a9da..4ba5d80b581ef 100644
--- a/lld/COFF/Chunks.cpp
+++ b/lld/COFF/Chunks.cpp
@@ -422,12 +422,6 @@ void SectionChunk::writeTo(uint8_t *buf) const {
 
     applyRelocation(buf + rel.VirtualAddress, rel);
   }
-
-  // Write the offset to EC entry thunk preceding section contents. The low bit
-  // is always set, so it's effectively an offset from the last byte of the
-  // offset.
-  if (Defined *entryThunk = getEntryThunk())
-    write32le(buf - sizeof(uint32_t), entryThunk->getRVA() - rva + 1);
 }
 
 void SectionChunk::applyRelocation(uint8_t *off,
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 076561807af47..62019f19292a1 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -2544,7 +2544,15 @@ void Writer::writeSections() {
     }
 
     parallelForEach(sec->chunks, [&](Chunk *c) {
-      c->writeTo(secBuf + c->getRVA() - sec->getRVA());
+      uint8_t *buf = secBuf + c->getRVA() - sec->getRVA();
+      c->writeTo(buf);
+
+      // Write the offset to EC entry thunk preceding section contents. The low
+      // bit is always set, so it's effectively an offset from the last byte of
+      // the offset.
+      if (Defined *entryThunk = c->getEntryThunk())
+        write32le(buf - sizeof(uint32_t),
+                  entryThunk->getRVA() - c->getRVA() + 1);
     });
   }
 }

[llvmbot]

@llvm/pr-subscribers-platform-windows

Author: Jacek Caban (cjacek)

Changes

To make it easier to add entry thunks to other chunk types.

---

Full diff: https://github.com/llvm/llvm-project/pull/151254.diff

2 Files Affected:

• (modified) lld/COFF/Chunks.cpp (-6)
• (modified) lld/COFF/Writer.cpp (+9-1)

diff --git a/lld/COFF/Chunks.cpp b/lld/COFF/Chunks.cpp
index 01752cdc6a9da..4ba5d80b581ef 100644
--- a/lld/COFF/Chunks.cpp
+++ b/lld/COFF/Chunks.cpp
@@ -422,12 +422,6 @@ void SectionChunk::writeTo(uint8_t *buf) const {
 
     applyRelocation(buf + rel.VirtualAddress, rel);
   }
-
-  // Write the offset to EC entry thunk preceding section contents. The low bit
-  // is always set, so it's effectively an offset from the last byte of the
-  // offset.
-  if (Defined *entryThunk = getEntryThunk())
-    write32le(buf - sizeof(uint32_t), entryThunk->getRVA() - rva + 1);
 }
 
 void SectionChunk::applyRelocation(uint8_t *off,
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index 076561807af47..62019f19292a1 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -2544,7 +2544,15 @@ void Writer::writeSections() {
     }
 
     parallelForEach(sec->chunks, [&](Chunk *c) {
-      c->writeTo(secBuf + c->getRVA() - sec->getRVA());
+      uint8_t *buf = secBuf + c->getRVA() - sec->getRVA();
+      c->writeTo(buf);
+
+      // Write the offset to EC entry thunk preceding section contents. The low
+      // bit is always set, so it's effectively an offset from the last byte of
+      // the offset.
+      if (Defined *entryThunk = c->getEntryThunk())
+        write32le(buf - sizeof(uint32_t),
+                  entryThunk->getRVA() - c->getRVA() + 1);
     });
   }
 }

[cjacek]

Split from a larger -arm64xsameaddress patch, which will use it for a same-address thunks.

[mstorsjo]

This is probably fine - it looks a bit unintuitive, but probably is good if it makes the following commit easier. However I don't quite see in which way this makes the later commit easier, as I don't see anything touching this area in that commit?

[cjacek]

With #151255, we also need entry thunk support for SameAddressThunkARM64EC. On top of this PR, that just requires overriding getEntryThunk. Before the recent change that moved the write logic, I also had to override writeTo to write the offset there (that’s not a big deal, so I can go back to that if preferred).

[mstorsjo]

With #151255, we also need entry thunk support for SameAddressThunkARM64EC. On top of this PR, that just requires overriding getEntryThunk. Before the recent change that moved the write logic, I also had to override writeTo to write the offset there (that’s not a big deal, so I can go back to that if preferred).

Ah, I see, thanks! Then this does indeed seem well motivated.