[PATCH] D66658: [ELF] Align the first section of a PT_LOAD even if its type is SHT_NOBITS

[Peter Collingbourne via Phabricator via llvm-commits]

pcc added a comment.

Thanks @MaskRay and @peter.smith for investigating this problem, I can confirm that this change fixes it for me.



================
Comment at: ELF/Writer.cpp:2277
+  // p_vaddr=p_offset (mod p_align).
+  if (os->type == SHT_NOBITS && !(os->ptLoad && os->ptLoad->firstSec == os))
     return off;
----------------
Maybe it would be better to reorder the if statements here to make the logic slightly easier to understand? This seems to work:
```
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index fde253796a1..f14951f403b 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -2269,8 +2269,16 @@ template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
 // same with its virtual address modulo the page size, so that the loader can
 // load executables without any address adjustment.
 static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
-  // File offsets are not significant for .bss sections. By convention, we keep
-  // section offsets monotonically increasing rather than setting to zero.
+  // The first section in a PT_LOAD has to have congruent offset and address
+  // module the page size.
+  if (os->ptLoad && os->ptLoad->firstSec == os) {
+    uint64_t alignment = std::max<uint64_t>(os->alignment, config->maxPageSize);
+    return alignTo(off, alignment, os->addr);
+  }
+
+  // File offsets are not significant for .bss sections other than the first one
+  // in a PT_LOAD. By convention, we keep section offsets monotonically
+  // increasing rather than setting to zero.
   if (os->type == SHT_NOBITS)
     return off;
 
@@ -2278,16 +2286,9 @@ static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
   if (!os->ptLoad)
     return alignTo(off, os->alignment);
 
-  // The first section in a PT_LOAD has to have congruent offset and address
-  // module the page size.
-  OutputSection *first = os->ptLoad->firstSec;
-  if (os == first) {
-    uint64_t alignment = std::max<uint64_t>(os->alignment, config->maxPageSize);
-    return alignTo(off, alignment, os->addr);
-  }
-
   // If two sections share the same PT_LOAD the file offset is calculated
   // using this formula: Off2 = Off1 + (VA2 - VA1).
+  OutputSection *first = os->ptLoad->firstSec;
   return first->offset + os->addr - first->addr;
 }
 
```


Repository:
  rLLD LLVM Linker

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  https://reviews.llvm.org/D66658/new/

https://reviews.llvm.org/D66658