Bug 1499915 - Remove support for the elfhack filler segment r=froydnj

This effectively backs out bug 822584, which worked around a similar
problem to what we are facing with Android xpcshell, being that the
crash reporter doesn't handle the address space "fragmentation" induced
by elfhack. The work around worked, at the expense of some added
complexity.

It was used for B2G only, and has effectively been unused since B2G was
retired.

Differential Revision: https://phabricator.services.mozilla.com/D9622

--HG--
extra : moz-landing-system : lando

build/unix/elfhack/elf.cpp

@@ -626,7 +626,7 @@ void ElfSegment::removeSection(ElfSection *section)
 
 unsigned int ElfSegment::getFileSize()
 {
-    if (type == PT_GNU_RELRO || isElfHackFillerSegment())
+    if (type == PT_GNU_RELRO)
         return filesz;
 
     if (sections.empty())
@@ -645,7 +645,7 @@ unsigned int ElfSegment::getFileSize()
 
 unsigned int ElfSegment::getMemSize()
 {
-    if (type == PT_GNU_RELRO || isElfHackFillerSegment())
+    if (type == PT_GNU_RELRO)
         return memsz;
 
     if (sections.empty())
@@ -662,10 +662,6 @@ unsigned int ElfSegment::getOffset()
         (sections.front()->getAddr() != vaddr))
         throw std::runtime_error("PT_GNU_RELRO segment doesn't start on a section start");
 
-    // Neither bionic nor glibc linkers seem to like when the offset of that segment is 0
-    if (isElfHackFillerSegment())
-        return vaddr;
-
     return sections.empty() ? 0 : sections.front()->getOffset();
 }
 
@@ -675,9 +671,6 @@ unsigned int ElfSegment::getAddr()
         (sections.front()->getAddr() != vaddr))
         throw std::runtime_error("PT_GNU_RELRO segment doesn't start on a section start");
 
-    if (isElfHackFillerSegment())
-        return vaddr;
-
     return sections.empty() ? 0 : sections.front()->getAddr();
 }
 

build/unix/elfhack/elfhack.cpp

@@ -464,7 +464,7 @@ void set_relative_reloc(Elf_Rela *rel, Elf *elf, unsigned int value) {
     rel->r_addend = value;
 }
 
-void maybe_split_segment(Elf *elf, ElfSegment *segment, bool fill)
+void maybe_split_segment(Elf *elf, ElfSegment *segment)
 {
     std::list<ElfSection *>::iterator it = segment->begin();
     for (ElfSection *last = *(it++); it != segment->end(); last = *(it++)) {
@@ -484,45 +484,12 @@ void maybe_split_segment(Elf *elf, ElfSegment *segment, bool fill)
             phdr.p_memsz = (unsigned int)-1;
             ElfSegment *newSegment = new ElfSegment(&phdr);
             elf->insertSegmentAfter(segment, newSegment);
-            ElfSection *section = *it;
             for (; it != segment->end(); ++it) {
                 newSegment->addSection(*it);
             }
             for (it = newSegment->begin(); it != newSegment->end(); ++it) {
                 segment->removeSection(*it);
             }
-            // Fill the virtual address space gap left between the two PT_LOADs
-            // with a new PT_LOAD with no permissions. This avoids the linker
-            // (especially bionic's) filling the gap with anonymous memory,
-            // which breakpad doesn't like.
-            // /!\ running strip on a elfhacked binary will break this filler
-            // PT_LOAD.
-            if (!fill)
-                break;
-            // Insert dummy segment to normalize the entire Elf with the header
-            // sizes adjusted, before inserting a filler segment.
-            {
-              memset(&phdr, 0, sizeof(phdr));
-              ElfSegment dummySegment(&phdr);
-              elf->insertSegmentAfter(segment, &dummySegment);
-              elf->normalize();
-              elf->removeSegment(&dummySegment);
-            }
-            ElfSection *previous = section->getPrevious();
-            phdr.p_type = PT_LOAD;
-            phdr.p_vaddr = (previous->getAddr() + previous->getSize() + segment->getAlign() - 1) & ~(segment->getAlign() - 1);
-            phdr.p_paddr = phdr.p_vaddr + segment->getVPDiff();
-            phdr.p_flags = 0;
-            phdr.p_align = 0;
-            phdr.p_filesz = (section->getAddr() & ~(newSegment->getAlign() - 1)) - phdr.p_vaddr;
-            phdr.p_memsz = phdr.p_filesz;
-            if (phdr.p_filesz) {
-                newSegment = new ElfSegment(&phdr);
-                assert(newSegment->isElfHackFillerSegment());
-                elf->insertSegmentAfter(segment, newSegment);
-            } else {
-                elf->normalize();
-            }
             break;
         }
     }
@@ -767,7 +734,7 @@ malformed:
 }
 
 template <typename Rel_Type>
-int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type2, bool force, bool fill)
+int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type2, bool force)
 {
     ElfDynamic_Section *dyn = elf->getDynSection();
     if (dyn == nullptr) {
@@ -1136,7 +1103,7 @@ int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type
     // Adjust PT_LOAD segments
     for (ElfSegment *segment = elf->getSegmentByType(PT_LOAD); segment;
          segment = elf->getSegmentByType(PT_LOAD, segment)) {
-        maybe_split_segment(elf, segment, fill);
+        maybe_split_segment(elf, segment);
     }
 
     // Ensure Elf sections will be at their final location.
@@ -1167,7 +1134,7 @@ static inline int backup_file(const char *name)
     return rename(name, fname.c_str());
 }
 
-void do_file(const char *name, bool backup = false, bool force = false, bool fill = false)
+void do_file(const char *name, bool backup = false, bool force = false)
 {
     std::ifstream file(name, std::ios::in|std::ios::binary);
     Elf elf(file);
@@ -1190,13 +1157,13 @@ void do_file(const char *name, bool backup = false, bool force = false, bool fil
     int exit = -1;
     switch (elf.getMachine()) {
     case EM_386:
-        exit = do_relocation_section<Elf_Rel>(&elf, R_386_RELATIVE, R_386_32, force, fill);
+        exit = do_relocation_section<Elf_Rel>(&elf, R_386_RELATIVE, R_386_32, force);
         break;
     case EM_X86_64:
-        exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE, R_X86_64_64, force, fill);
+        exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE, R_X86_64_64, force);
         break;
     case EM_ARM:
-        exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32, force, fill);
+        exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32, force);
         break;
     }
     if (exit == 0) {
@@ -1246,12 +1213,6 @@ void undo_file(const char *name, bool backup = false)
         return;
     }
     second = elf.getSegmentByType(PT_LOAD, first);
-    ElfSegment *filler = nullptr;
-    // If the second PT_LOAD is a filler from elfhack --fill, check the third.
-    if (second->isElfHackFillerSegment()) {
-        filler = second;
-        second = elf.getSegmentByType(PT_LOAD, filler);
-    }
     if (second->getFlags() != first->getFlags()) {
         fprintf(stderr, "Couldn't identify elfhacked PT_LOAD segments. Skipping\n");
         return;
@@ -1263,8 +1224,6 @@ void undo_file(const char *name, bool backup = false)
         first->addSection(*section);
 
     elf.removeSegment(second);
-    if (filler)
-        elf.removeSegment(filler);
 
     if (backup && backup_file(name) != 0) {
         fprintf(stderr, "Couln't create backup file\n");
@@ -1281,7 +1240,6 @@ int main(int argc, char *argv[])
     bool backup = false;
     bool force = false;
     bool revert = false;
-    bool fill = false;
     char *lastSlash = rindex(argv[0], '/');
     if (lastSlash != nullptr)
         rundir = strndup(argv[0], lastSlash - argv[0]);
@@ -1292,12 +1250,10 @@ int main(int argc, char *argv[])
             backup = true;
         else if (strcmp(argv[arg], "-r") == 0)
             revert = true;
-        else if (strcmp(argv[arg], "--fill") == 0)
-            fill = true;
         else if (revert) {
             undo_file(argv[arg], backup);
         } else
-            do_file(argv[arg], backup, force, fill);
+            do_file(argv[arg], backup, force);
     }
 
     free(rundir);

build/unix/elfhack/elfxx.h

@@ -486,10 +486,6 @@ public:
     std::list<ElfSection *>::iterator end() { return sections.end(); }
 
     void clear();
-
-    bool isElfHackFillerSegment() {
-      return type == PT_LOAD && flags == 0;
-    }
 private:
     unsigned int type;
     int v_p_diff; // Difference between physical and virtual address