[ELF][PPC64] Fix potentially corrupted section content with empty .got

MaskRay · MaskRay · commit 28d05d672300 · 2022-08-05T15:22:57.000-07:00
D91426 makes .got possibly empty while needed. If .got and .data have the same
address, and .got's content is written after .data, the first word of .data will
be corrupted.

The bug is not testable without D131247.
diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
@@ -678,6 +678,9 @@ bool GotSection::isNeeded() const {
 }
 
 void GotSection::writeTo(uint8_t *buf) {
+  // On PPC64 .got may be needed but empty. Skip the write.
+  if (size == 0)
+    return;
   target->writeGotHeader(buf);
   relocateAlloc(buf, buf + size);
 }

Original file line number	Diff line number	Diff line change
`@@ -678,6 +678,9 @@ bool GotSection::isNeeded() const {`
`678`	`678`	`}`
`679`	`679`
`680`	`680`	`void GotSection::writeTo(uint8_t *buf) {`
	`681`	`+ // On PPC64 .got may be needed but empty. Skip the write.`
	`682`	`+ if (size == 0)`
	`683`	`+ return;`
`681`	`684`	`target->writeGotHeader(buf);`
`682`	`685`	`relocateAlloc(buf, buf + size);`
`683`	`686`	`}`