[PATCH] D18948: [ELF][MIPS] Create GOT entries for R_MIPS_REL32 dynamic relocations

[Simon Atanasyan via llvm-commits]

atanasyan updated this revision to Diff 53840.
atanasyan added a comment.

Rebase the patch.


Repository:
  rL LLVM

http://reviews.llvm.org/D18948

Files:
  ELF/Writer.cpp
  test/ELF/mips-32.s

Index: test/ELF/mips-32.s
===================================================================
--- test/ELF/mips-32.s
+++ test/ELF/mips-32.s
@@ -4,13 +4,15 @@
 # RUN: ld.lld -shared %t-be.o -o %t-be.so
 # RUN: llvm-objdump -t -s %t-be.so \
 # RUN:   | FileCheck -check-prefix=SYM -check-prefix=BE %s
-# RUN: llvm-readobj -r -dynamic-table %t-be.so | FileCheck -check-prefix=REL %s
+# RUN: llvm-readobj -r -dynamic-table -mips-plt-got %t-be.so \
+# RUN:   | FileCheck -check-prefix=REL %s
 
 # RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux %s -o %t-el.o
 # RUN: ld.lld -shared %t-el.o -o %t-el.so
 # RUN: llvm-objdump -t -s %t-el.so \
 # RUN:   | FileCheck -check-prefix=SYM -check-prefix=EL %s
-# RUN: llvm-readobj -r -dynamic-table %t-el.so | FileCheck -check-prefix=REL %s
+# RUN: llvm-readobj -r -dynamic-table -mips-plt-got %t-el.so \
+# RUN:   | FileCheck -check-prefix=REL %s
 
 # REQUIRES: mips
 
@@ -54,3 +56,23 @@
 # REL:   Tag        Type                 Name/Value
 # REL:   0x00000012 RELSZ                16 (bytes)
 # REL:   0x00000013 RELENT               8 (bytes)
+
+# REL:      Primary GOT {
+# REL-NEXT:   Canonical gp value:
+# REL-NEXT:   Reserved entries [
+# REL:        ]
+# REL-NEXT:   Local entries [
+# REL-NEXT:   ]
+# REL-NEXT:   Global entries [
+# REL-NEXT:     Entry {
+# REL-NEXT:       Address:
+# REL-NEXT:       Access:
+# REL-NEXT:       Initial: 0x30004
+# REL-NEXT:       Value: 0x30004
+# REL-NEXT:       Type: Object
+# REL-NEXT:       Section: .data
+# REL-NEXT:       Name: v2
+# REL-NEXT:     }
+# REL-NEXT:   ]
+# REL-NEXT:   Number of TLS and multi-GOT entries: 0
+# REL-NEXT: }
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -600,6 +600,23 @@
       // We don't know anything about the finaly symbol. Just ask the dynamic
       // linker to handle the relocation for us.
       AddDyn({Target->getDynRel(Type), C.OutSec, Offset, false, &Body, Addend});
+      // MIPS ABI turns using of GOT and dynamic relocations inside out.
+      // While regular ABI uses dynamic relocations to fill up GOT entries
+      // MIPS ABI requires dynamic linker to fills up GOT entries using
+      // specially sorted dynamic symbol table. This affects even dynamic
+      // relocations against symbols which do not require GOT entries
+      // creation explicitly, i.e. do not have any GOT-relocations. So if
+      // a preemptible symbol has a dynamic relocation we anyway have
+      // to create a GOT entry for it.
+      // If a non-preemptible symbol has a dynamic relocation against it,
+      // dynamic linker takes it st_value, adds offset and writes down
+      // result of the dynamic relocation. In case of preemptible symbol
+      // dynamic linker performs symbol resolution, writes the symbol value
+      // to the GOT entry and reads the GOT entry when it needs to perform
+      // a dynamic relocation.
+      // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
+      if (Config->EMachine == EM_MIPS && !Body.isInGot())
+        Out<ELFT>::Got->addEntry(Body);
       continue;
     }
 


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