[PATCH] D79211: [lld-macho] Support pc-relative section relocations

[Jez Ng via Phabricator via llvm-commits]

int3 created this revision.
int3 added reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

So far we've only supported symbol relocations.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D79211

Files:
  lld/MachO/InputFiles.cpp
  lld/MachO/InputSection.cpp
  lld/MachO/InputSection.h
  lld/test/MachO/relocations.s


Index: lld/test/MachO/relocations.s
===================================================================
--- lld/test/MachO/relocations.s
+++ lld/test/MachO/relocations.s
@@ -12,9 +12,12 @@
 # CHECK-LABEL: <_main>:
 ## Test X86_64_RELOC_BRANCH
 # CHECK:       callq 0x[[#%x, F_ADDR]] <_f>
-## Test X86_64_RELOC_SIGNED
+## Test extern (symbol) X86_64_RELOC_SIGNED
 # CHECK:       leaq [[#%u, STR_OFF:]](%rip), %rsi
 # CHECK-NEXT:  [[#%x, CSTRING_ADDR - STR_OFF]]
+## Test non-extern (section) X86_64_RELOC_SIGNED
+# CHECK:       leaq [[#%u, LSTR_OFF:]](%rip), %rsi
+# CHECK-NEXT:  [[#%x, CSTRING_ADDR + 22 - LSTR_OFF]]
 
 .section __TEXT,__text
 .globl _main, _f
@@ -26,11 +29,21 @@
 _f:
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
-  leaq str(%rip), %rsi
-  mov $13, %rdx # length of str
+  leaq _str(%rip), %rsi
+  mov $21, %rdx # length of str
+  syscall
+
+  movl $0x2000004, %eax # write() syscall
+  mov $1, %rdi # stdout
+  leaq L_.str(%rip), %rsi
+  mov $15, %rdx # length of str
   syscall
   ret
 
 .section __TEXT,__cstring
-str:
-  .asciz "Hello world!\n"
+## References to this generate a symbol relocation
+_str:
+  .asciz "Local defined symbol\n"
+## References to this generate a section relocation
+L_.str:
+  .asciz "Private symbol\n"
Index: lld/MachO/InputSection.h
===================================================================
--- lld/MachO/InputSection.h
+++ lld/MachO/InputSection.h
@@ -40,6 +40,8 @@
   StringRef name;
   StringRef segname;
 
+  // This provides access to the address of the section in the input file.
+  const llvm::MachO::section_64 *header;
   ArrayRef<uint8_t> data;
 
   // TODO these properties ought to live in an OutputSection class.
Index: lld/MachO/InputSection.cpp
===================================================================
--- lld/MachO/InputSection.cpp
+++ lld/MachO/InputSection.cpp
@@ -47,7 +47,16 @@
       else
         va = s->getVA();
     } else {
-      fatal("TODO: Non-extern relocations are not supported");
+      uint32_t sectIdx = rel.r_symbolnum - 1;
+      if (sectIdx > file->sections.size())
+        fatal("Relocation section index is greater than number of sections");
+      InputSection *isec = file->sections[sectIdx];
+      va = isec->addr;
+      // The implicit addend for pcrel section relocations is the pcrel offset
+      // in terms of the addresses in the input file. Here we adjust it so that
+      // it describes the offset from the start of the relocated section.
+      // TODO: Figure out what to do for non-pcrel section relocations.
+      addend -= isec->header->addr - (rel.r_address + 4);
     }
 
     uint64_t val = va + addend;
Index: lld/MachO/InputFiles.cpp
===================================================================
--- lld/MachO/InputFiles.cpp
+++ lld/MachO/InputFiles.cpp
@@ -134,6 +134,7 @@
   for (const section_64 &sec : sections) {
     InputSection *isec = make<InputSection>();
     isec->file = this;
+    isec->header = &sec;
     isec->name = StringRef(sec.sectname, strnlen(sec.sectname, 16));
     isec->segname = StringRef(sec.segname, strnlen(sec.segname, 16));
     isec->data = {buf + sec.offset, static_cast<size_t>(sec.size)};


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