Bug 822584 - Workaround in elfhack to accomodate for breakpad not handling the memory mapping induced by the elfhack/bionic linker combination. r=nfroyd,a=akeybl

--HG--
extra : transplant_source : %E0%17%F3%A2m%1ASd%11%01%0E2%D6%C2%C3%D0h%8E%CF%3B

build/unix/elfhack/elf.cpp

@@ -585,7 +585,7 @@ void ElfSegment::removeSection(ElfSection *section)
 
 unsigned int ElfSegment::getFileSize()
 {
-    if (type == PT_GNU_RELRO)
+    if (type == PT_GNU_RELRO || isElfHackFillerSegment())
         return filesz;
 
     if (sections.empty())
@@ -604,7 +604,7 @@ unsigned int ElfSegment::getFileSize()
 
 unsigned int ElfSegment::getMemSize()
 {
-    if (type == PT_GNU_RELRO)
+    if (type == PT_GNU_RELRO || isElfHackFillerSegment())
         return memsz;
 
     if (sections.empty())
@@ -621,6 +621,10 @@ 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();
 }
 
@@ -630,6 +634,9 @@ 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

@@ -376,7 +376,7 @@ void set_relative_reloc(Elf_Rela *rel, Elf *elf, unsigned int value) {
     rel->r_addend = value;
 }
 
-void maybe_split_segment(Elf *elf, ElfSegment *segment)
+void maybe_split_segment(Elf *elf, ElfSegment *segment, bool fill)
 {
     std::list<ElfSection *>::iterator it = segment->begin();
     for (ElfSection *last = *(it++); it != segment->end(); last = *(it++)) {
@@ -396,19 +396,40 @@ void maybe_split_segment(Elf *elf, ElfSegment *segment)
             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;
+            ElfSection *previous = section->getPrevious();
+            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);
+            }
             break;
         }
     }
 }
 
 template <typename Rel_Type>
-int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type2, bool force)
+int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type2, bool force, bool fill)
 {
     ElfDynamic_Section *dyn = elf->getDynSection();
     if (dyn ==NULL) {
@@ -568,7 +589,7 @@ 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);
+        maybe_split_segment(elf, segment, fill);
     }
 
     // Ensure Elf sections will be at their final location.
@@ -599,7 +620,7 @@ 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)
+void do_file(const char *name, bool backup = false, bool force = false, bool fill = false)
 {
     std::ifstream file(name, std::ios::in|std::ios::binary);
     Elf elf(file);
@@ -622,13 +643,13 @@ void do_file(const char *name, bool backup = false, bool force = false)
     int exit = -1;
     switch (elf.getMachine()) {
     case EM_386:
-        exit = do_relocation_section<Elf_Rel>(&elf, R_386_RELATIVE, R_386_32, force);
+        exit = do_relocation_section<Elf_Rel>(&elf, R_386_RELATIVE, R_386_32, force, fill);
         break;
     case EM_X86_64:
-        exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE, R_X86_64_64, force);
+        exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE, R_X86_64_64, force, fill);
         break;
     case EM_ARM:
-        exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32, force);
+        exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32, force, fill);
         break;
     }
     if (exit == 0) {
@@ -677,8 +698,14 @@ void undo_file(const char *name, bool backup = false)
 
     ElfSegment *first = elf.getSegmentByType(PT_LOAD);
     ElfSegment *second = elf.getSegmentByType(PT_LOAD, first);
+    ElfSegment *filler = NULL;
+    // 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, "First two PT_LOAD segments don't have the same flags. Skipping\n");
+        fprintf(stderr, "Couldn't identify elfhacked PT_LOAD segments. Skipping\n");
         return;
     }
     // Move sections from the second PT_LOAD to the first, and remove the
@@ -688,6 +715,8 @@ 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");
@@ -704,6 +733,7 @@ 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 != NULL)
         rundir = strndup(argv[0], lastSlash - argv[0]);
@@ -714,10 +744,12 @@ int main(int argc, char *argv[])
             backup = true;
         else if (strcmp(argv[arg], "-r") == 0)
             revert = true;
-        else if (revert)
+        else if (strcmp(argv[arg], "--fill") == 0)
+            fill = true;
+        else if (revert) {
             undo_file(argv[arg], backup);
-        else
-            do_file(argv[arg], backup, force);
+        } else
+            do_file(argv[arg], backup, force, fill);
     }
 
     free(rundir);

build/unix/elfhack/elfxx.h

@@ -460,6 +460,10 @@ 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