Bug 956398 - Support text relocations in the custom linker. r=nfroyd

mozglue/linker/CustomElf.cpp

@@ -64,6 +64,13 @@ void debug_phdr(const char *type, const Phdr *phdr)
             phdr->p_flags & PF_W ? 'w' : '-', phdr->p_flags & PF_X ? 'x' : '-');
 }
 
+static int p_flags_to_mprot(Word flags)
+{
+  return ((flags & PF_X) ? PROT_EXEC : 0) |
+         ((flags & PF_W) ? PROT_WRITE : 0) |
+         ((flags & PF_R) ? PROT_READ : 0);
+}
+
 void
 __void_stub(void)
 {
@@ -225,6 +232,28 @@ CustomElf::Load(Mappable *mappable, const char *path, int flags)
   if (!elf->InitDyn(dyn))
     return nullptr;
 
+  if (elf->has_text_relocs) {
+    for (std::vector<const Phdr *>::iterator it = pt_loads.begin();
+         it < pt_loads.end(); ++it)
+      mprotect(PageAlignedPtr(elf->GetPtr((*it)->p_vaddr)),
+               PageAlignedEndPtr((*it)->p_memsz),
+               p_flags_to_mprot((*it)->p_flags) | PROT_WRITE);
+  }
+
+  if (!elf->Relocate() || !elf->RelocateJumps())
+    return nullptr;
+
+  if (elf->has_text_relocs) {
+    for (std::vector<const Phdr *>::iterator it = pt_loads.begin();
+         it < pt_loads.end(); ++it)
+      mprotect(PageAlignedPtr(elf->GetPtr((*it)->p_vaddr)),
+               PageAlignedEndPtr((*it)->p_memsz),
+               p_flags_to_mprot((*it)->p_flags));
+  }
+
+  if (!elf->CallInit())
+    return nullptr;
+
 #ifdef __ARM_EABI__
   if (arm_exidx_phdr)
     elf->arm_exidx.InitSize(elf->GetPtr(arm_exidx_phdr->p_vaddr),
@@ -423,9 +452,7 @@ CustomElf::LoadSegment(const Phdr *pt_load) const
     return false;;
   }
 
-  int prot = ((pt_load->p_flags & PF_X) ? PROT_EXEC : 0) |
-             ((pt_load->p_flags & PF_W) ? PROT_WRITE : 0) |
-             ((pt_load->p_flags & PF_R) ? PROT_READ : 0);
+  int prot = p_flags_to_mprot(pt_load->p_flags);
 
   /* Mmap at page boundary */
   Addr align = PageSize();
@@ -549,8 +576,8 @@ CustomElf::InitDyn(const Phdr *pt_dyn)
         }
         break;
       case DT_TEXTREL:
-        LOG("%s: Text relocations are not supported", GetPath());
-        return false;
+        has_text_relocs = true;
+        break;
       case DT_STRSZ: /* Ignored */
         debug_dyn("DT_STRSZ", dyn);
         break;
@@ -620,8 +647,7 @@ CustomElf::InitDyn(const Phdr *pt_dyn)
            Addr flags = dyn->d_un.d_val;
            /* Treat as a DT_TEXTREL tag */
            if (flags & DF_TEXTREL) {
-             LOG("%s: Text relocations are not supported", GetPath());
-             return false;
+             has_text_relocs = true;
            }
            /* we can treat this like having a DT_SYMBOLIC tag */
            flags &= ~DF_SYMBOLIC;
@@ -677,8 +703,7 @@ CustomElf::InitDyn(const Phdr *pt_dyn)
     dependencies.push_back(handle);
   }
 
-  /* Finish initialization */
-  return Relocate() && RelocateJumps() && CallInit();
+  return true;
 }
 
 bool

mozglue/linker/CustomElf.h

@@ -76,7 +76,12 @@ private:
    * Private constructor
    */
   CustomElf(Mappable *mappable, const char *path)
-  : LibHandle(path), mappable(mappable), init(0), fini(0), initialized(false)
+  : LibHandle(path)
+  , mappable(mappable)
+  , init(0)
+  , fini(0)
+  , initialized(false)
+  , has_text_relocs(false)
   { }
 
   /**
@@ -193,6 +198,8 @@ private:
 
   bool initialized;
 
+  bool has_text_relocs;
+
 #ifdef __ARM_EABI__
   /* ARM.exidx information used by FindExidx */
   Array<uint32_t[2]> arm_exidx;