[PATCH] D39493: [ELF] Fix DT_MIPS_LOCAL_GOTNO value when using linker scripts to change section sizes

[James Henderson via Phabricator via llvm-commits]

jhenderson created this revision.
Herald added subscribers: arichardson, sdardis, emaste.

The MIPS GOT section has a number of local entries based on the number of pages needed for output sections referenced by GOT page relocations. The number is recorded in the DT_MIPS_LOCAL_GOTNO dynamic section tag. However, the dynamic tag is added before assignAddresses has been called, meaning that any section size used to calculate the value will not include size modifications caused by linker scripts, thunks, etc.

This change moves the calculation of DT_MIPS_LOCAL_GOTNO until writeTo, by which time the output section sizes have been finalized.

I have spun it off from https://reviews.llvm.org/D38361, because the behaviour is already broken.


https://reviews.llvm.org/D39493

Files:
  ELF/SyntheticSections.cpp
  test/ELF/mips-got-script.s


Index: test/ELF/mips-got-script.s
===================================================================
--- test/ELF/mips-got-script.s
+++ test/ELF/mips-got-script.s
@@ -0,0 +1,47 @@
+# Check number of got entries is adjusted for linker script-added space.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS { .data : { *(.data.1); . += 0x10000; *(.data.2) } }" > %t.script
+# RUN: ld.lld %t.o -shared -o %t.so -T %t.script
+# RUN: llvm-readobj -mips-plt-got -dynamic-table %t.so | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK: 0x7000000A MIPS_LOCAL_GOTNO 5
+#                                    ^-- 2 * header + 3 local entries
+# CHECK:      Local entries [
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32744
+# CHECK-NEXT:     Initial: 0x0
+#                          ^-- loc1
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32740
+# CHECK-NEXT:     Initial: 0x10000
+#                          ^-- loc2
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32736
+# CHECK-NEXT:     Initial: 0x20000
+#                          ^-- redundant
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+
+  .text
+  .globl  foo
+foo:
+  lw      $t0, %got(loc1)($gp)
+  addi    $t0, $t0, %lo(loc1)
+  lw      $t0, %got(loc2)($gp)
+  addi    $t0, $t0, %lo(loc2)
+
+  .section .data.1,"aw",%progbits
+loc1:
+  .word 0
+
+  .section .data.2,"aw",%progbits
+loc2:
+  .word 0
Index: ELF/SyntheticSections.cpp
===================================================================
--- ELF/SyntheticSections.cpp
+++ ELF/SyntheticSections.cpp
@@ -1147,7 +1147,11 @@
     add({DT_MIPS_FLAGS, RHF_NOTPOT});
     add({DT_MIPS_BASE_ADDRESS, Target->getImageBase()});
     add({DT_MIPS_SYMTABNO, InX::DynSymTab->getNumSymbols()});
-    add({DT_MIPS_LOCAL_GOTNO, InX::MipsGot->getLocalEntriesNum()});
+
+    // The number of local got entries has not yet been finalized. This value
+    // will be set in writeTo().
+    add({DT_MIPS_LOCAL_GOTNO, uint64_t(0)});
+
     if (const SymbolBody *B = InX::MipsGot->getFirstGlobalEntry())
       add({DT_MIPS_GOTSYM, B->DynsymIndex});
     else
@@ -1182,7 +1186,10 @@
       P->d_un.d_ptr = E.Sym->getVA();
       break;
     case Entry::PlainInt:
-      P->d_un.d_val = E.Val;
+      if (E.Tag == DT_MIPS_LOCAL_GOTNO)
+        P->d_un.d_val = InX::MipsGot->getLocalEntriesNum();
+      else
+        P->d_un.d_val = E.Val;
       break;
     }
     ++P;


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