[lld] b00f0d4 - [mips] Support 64-bit relative relocations

[Simon Atanasyan via llvm-commits]

Author: Simon Atanasyan
Date: 2020-06-02T11:44:11+03:00
New Revision: b00f0d4238cb34a54073cc5ab7e2060d58f69e3f

URL: https://github.com/llvm/llvm-project/commit/b00f0d4238cb34a54073cc5ab7e2060d58f69e3f
DIFF: https://github.com/llvm/llvm-project/commit/b00f0d4238cb34a54073cc5ab7e2060d58f69e3f.diff

LOG: [mips] Support 64-bit relative relocations

MIPS 64-bit ABI does not provide special PC-relative relocation like
R_MIPS_PC32 in 32-bit case. But we can use a "chain of relocation"
defined by N64 ABIs. In that case one relocation record might contain up
to three relocations which applied sequentially. Width of a final relocation
mask applied to the result of relocation depends on the last relocation
in the chain. In case of 64-bit PC-relative relocation we need the following
chain: `R_MIPS_PC32 | R_MIPS_64`. The first relocation calculates an
offset, but does not truncate the result. The second relocation just
apply calculated result as a 64-bit value.

The 64-bit PC-relative relocation might be useful in generation of
`.eh_frame` sections to escape passing `-Wl,-z,notext` flags to linker.

Differential Revision: https://reviews.llvm.org/D80390

Added: 
    lld/test/ELF/mips-pc64.s

Modified: 
    llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
    llvm/test/MC/Mips/relocation-n64.s
    llvm/test/MC/Mips/unsupported-relocation.s

Removed: 
    


################################################################################
diff  --git a/lld/test/ELF/mips-pc64.s b/lld/test/ELF/mips-pc64.s
new file mode 100644
index 000000000000..6248c67f735d
--- /dev/null
+++ b/lld/test/ELF/mips-pc64.s
@@ -0,0 +1,24 @@
+# REQUIRES: mips
+
+# Check handling of 64-bit pc-realtive relocation.
+
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-linux %s -o %t.o
+# RUN: echo 'SECTIONS { \
+# RUN:         .text 0x10000 : { *(.text) } \
+# RUN:         .data 0x30000 : { *(.data) } \
+# RUN:       }' > %t.script
+# RUN: ld.lld -shared %t.o -T %t.script -o %t
+# RUN: llvm-readelf -x .data %t | FileCheck %s
+
+# CHECK:      Hex dump of section '.data':
+# CHECK-NEXT:  0x00030000 ffffffff fffffff0 00000001 fffdffe8
+
+  .option pic2
+  .text
+foo:
+  nop
+  .data
+v0:
+  .quad foo+0x1fff0-.
+v1:
+  .quad foo+0x1fffffff0-.

diff  --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
index ee2e8779eb0d..fc0154d414fb 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp
@@ -234,14 +234,15 @@ unsigned MipsELFObjectWriter::getRelocType(MCContext &Ctx,
   case Mips::fixup_Mips_32:
   case FK_Data_4:
     return IsPCRel ? ELF::R_MIPS_PC32 : ELF::R_MIPS_32;
+  case Mips::fixup_Mips_64:
+  case FK_Data_8:
+    return IsPCRel
+               ? setRTypes(ELF::R_MIPS_PC32, ELF::R_MIPS_64, ELF::R_MIPS_NONE)
+               : ELF::R_MIPS_64;
   }
 
   if (IsPCRel) {
     switch (Kind) {
-    case FK_Data_8:
-      Ctx.reportError(Fixup.getLoc(),
-                      "MIPS does not support 64-bit PC-relative relocations");
-      return ELF::R_MIPS_NONE;
     case Mips::fixup_Mips_Branch_PCRel:
     case Mips::fixup_Mips_PC16:
       return ELF::R_MIPS_PC16;
@@ -277,9 +278,6 @@ unsigned MipsELFObjectWriter::getRelocType(MCContext &Ctx,
   }
 
   switch (Kind) {
-  case Mips::fixup_Mips_64:
-  case FK_Data_8:
-    return ELF::R_MIPS_64;
   case FK_DTPRel_4:
     return ELF::R_MIPS_TLS_DTPREL32;
   case FK_DTPRel_8:

diff  --git a/llvm/test/MC/Mips/relocation-n64.s b/llvm/test/MC/Mips/relocation-n64.s
index 155ac20653a9..297b1a696c2b 100644
--- a/llvm/test/MC/Mips/relocation-n64.s
+++ b/llvm/test/MC/Mips/relocation-n64.s
@@ -70,4 +70,6 @@
         .word 0
 bar:
         .word 1
+        .option pic2
+        .quad foo+0x1fffffff0-.               // RELOC: R_MIPS_PC32/R_MIPS_64/R_MIPS_NONE foo 0x1FFFFFFF0
 // DATA-LABEL: Section {

diff  --git a/llvm/test/MC/Mips/unsupported-relocation.s b/llvm/test/MC/Mips/unsupported-relocation.s
index 258b48399873..311c0c7d60f2 100644
--- a/llvm/test/MC/Mips/unsupported-relocation.s
+++ b/llvm/test/MC/Mips/unsupported-relocation.s
@@ -11,5 +11,3 @@ foo:
 # CHECK: :[[@LINE-1]]:17: error: MIPS does not support one byte relocations
         .byte   x+1
 # CHECK: :[[@LINE-1]]:17: error: MIPS does not support one byte relocations
-        .quad   x-foo
-# CHECK: :[[@LINE-1]]:17: error: MIPS does not support 64-bit PC-relative relocations