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elf-cache.cc
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elf-cache.cc
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#include "elf-cache.h"
#include "ns3/log.h"
#include "ns3/assert.h"
#include "ns3/fatal-error.h"
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <sstream>
#include <string.h>
#include <sys/mman.h>
#include <gnu/lib-names.h>
namespace ns3 {
NS_LOG_COMPONENT_DEFINE ("DceElfCache");
ElfCache::ElfCache (std::string directory, uint32_t uid)
: m_directory (directory),
m_uid (uid)
{
struct Overriden overriden;
overriden.from = LIBC_SO;
overriden.to = "libc-ns3.so";
m_overriden.push_back (overriden);
overriden.from = LIBPTHREAD_SO;
overriden.to = "libpthread-ns3.so";
m_overriden.push_back (overriden);
overriden.from = LIBRT_SO;
overriden.to = "librt-ns3.so";
m_overriden.push_back (overriden);
overriden.from = LIBM_SO;
overriden.to = "libm-ns3.so";
m_overriden.push_back (overriden);
overriden.from = LIBDL_SO;
overriden.to = "libdl-ns3.so";
m_overriden.push_back (overriden);
}
std::string
ElfCache::GetBasename (std::string filename) const
{
std::string::size_type tmp = filename.find_last_of ("/");
if (tmp == std::string::npos)
{
return filename;
}
return filename.substr (tmp + 1, filename.size () - (tmp + 1));
}
void
ElfCache::CopyFile (std::string source, std::string destination) const
{
NS_LOG_FUNCTION (this << source << destination);
int src = open (source.c_str (), O_RDONLY);
int dst = open (destination.c_str (), O_WRONLY | O_CREAT | O_TRUNC, S_IRWXU);
uint8_t buffer[1024];
ssize_t bytes_read = read (src, buffer, 1024);
while (bytes_read > 0)
{
ssize_t bytes_written = 0;
while (bytes_written != bytes_read)
{
ssize_t written = write (dst, buffer + bytes_written, bytes_read - bytes_written);
bytes_written += written;
}
bytes_read = read (src, buffer, 1024);
}
close (src);
close (dst);
NS_LOG_DEBUG ("copied " << source << " to " << destination);
}
long
ElfCache::GetDtStrTab (ElfW(Dyn) *dyn, long baseAddress) const
{
bool prelinked = false;
long dt_strtab = 0;
while (dyn->d_tag != DT_NULL)
{
if (dyn->d_tag == DT_STRTAB)
{
dt_strtab = dyn->d_un.d_val;
}
else if (dyn->d_tag == DT_GNU_PRELINKED)
{
prelinked = true;
}
dyn++;
}
if (prelinked)
{
dt_strtab -= baseAddress;
}
return dt_strtab;
}
unsigned long
ElfCache::GetBaseAddress (ElfW(Phdr) *phdr, long phnum) const
{
unsigned long end = ~0; // the max value storable in a uint64_t
unsigned long base = end;
for (long i = 0; i < phnum; i++, phdr++)
{
if (phdr->p_type == PT_LOAD)
{
unsigned long ph_base = phdr->p_vaddr & ~(phdr->p_align - 1);
if (ph_base < base)
{
base = ph_base;
}
}
}
if (base == end)
{
NS_LOG_ERROR ("Could not find base address.");
}
return base;
}
uint8_t
ElfCache::NumberToChar (uint8_t c) const
{
NS_ASSERT (c <= 60);
if (c < 10)
{
return c + 0x30;
}
else if (c < (10 + 25))
{
return c - 10 + 0x41;
}
else if (c < (10 + 25 + 25))
{
return c - (10 + 25) + 0x61;
}
return 0; // quiet compiler
}
void
ElfCache::WriteString (char *str, uint32_t uid) const
{
// we use base 4 chars in base 60.
if (uid >= 60 * 60 * 60 * 60)
{
NS_FATAL_ERROR ("Please, report a bug: not enough unique strings for loaded code.");
}
uint8_t a = uid % 60;
uint8_t b = (uid / 60) % 60;
uint8_t c = (uid / 3600) % 60;
uint8_t d = (uid / 216000) % 60;
str[0] = NumberToChar (d);
str[1] = NumberToChar (c);
str[2] = NumberToChar (b);
str[3] = NumberToChar (a);
NS_LOG_DEBUG ("wrote " << str);
}
struct ElfCache::FileInfo
ElfCache::EditBuffer (uint8_t *map, uint32_t selfId) const
{
ElfW (Ehdr) *header = (ElfW (Ehdr) *)map;
ElfW (Phdr) * phdr = (ElfW (Phdr) *)(map + header->e_phoff);
ElfW (Dyn) * dyn = 0;
long base_address = GetBaseAddress (phdr, header->e_phnum);
// find DYNAMIC and fill DataSection
struct FileInfo fileInfo;
if (header->e_type != ET_DYN)
{
fileInfo.p_vaddr = -1;
return fileInfo;
}
ElfW (Phdr) * pt_load_rw = 0;
ElfW (Phdr) * pt_gnu_relro = 0;
for (uint32_t i = 0; i < header->e_phnum; i++, phdr++)
{
switch (phdr->p_type)
{
case PT_LOAD:
if (phdr->p_flags & PF_W)
{
// data section !
pt_load_rw = phdr;
}
break;
case PT_DYNAMIC:
// now, seek DT_NEEDED
dyn = (ElfW (Dyn) *)(map + phdr->p_offset);
break;
case PT_GNU_RELRO:
pt_gnu_relro = phdr;
break;
}
}
NS_ASSERT (pt_load_rw != 0);
fileInfo.p_vaddr = pt_load_rw->p_vaddr;
fileInfo.p_memsz = pt_load_rw->p_memsz;
if (pt_gnu_relro != 0)
{
NS_ASSERT (pt_gnu_relro->p_vaddr == pt_load_rw->p_vaddr);
fileInfo.p_vaddr += pt_gnu_relro->p_memsz;
fileInfo.p_memsz -= pt_gnu_relro->p_memsz;
}
// first, Patch the DT_NEEDED, and, DT_SONAME entries
// and save the DT_INIT entry
long dt_strtab = GetDtStrTab (dyn, base_address);
long dt_init = 0;
ElfW (Dyn) * cur = dyn;
while (cur->d_tag != DT_NULL)
{
if (cur->d_tag == DT_NEEDED)
{
char *needed = (char *)(map + dt_strtab + cur->d_un.d_val);
if (std::string (needed) != "ld-linux-x86-64.so.2"
&& std::string (needed) != "ld-linux.so.2")
{
uint32_t id = GetDepId (needed);
fileInfo.deps.push_back (id);
WriteString (needed, id);
}
}
else if (cur->d_tag == DT_SONAME)
{
char *soname = (char *)(map + dt_strtab + cur->d_un.d_val);
WriteString (soname, selfId);
}
else if (cur->d_tag == DT_INIT)
{
dt_init = cur->d_un.d_val;
}
cur++;
}
// then, eliminate DT_FINI, DT_FINI_ARRAY and DT_FINI_ARRAYSZ
cur = dyn;
while (cur->d_tag != DT_NULL)
{
if (cur->d_tag == DT_FINI)
{
cur->d_tag = DT_INIT;
cur->d_un.d_val = dt_init;
}
else if (cur->d_tag == DT_FINI_ARRAYSZ)
{
cur->d_un.d_val = 0;
}
cur++;
}
return fileInfo;
}
struct ElfCache::FileInfo
ElfCache::EditFile (std::string filename, uint32_t selfId) const
{
NS_LOG_FUNCTION (this << filename);
int fd = ::open (filename.c_str (), O_RDWR);
NS_ASSERT_MSG (fd != -1, "unable to open file=" << filename << " error=" << strerror (errno));
struct stat st;
int retval = ::fstat (fd, &st);
NS_ASSERT_MSG (retval == 0, "unable to fstat file=" << filename << " error=" << strerror (errno));
uint64_t size = st.st_size;
uint8_t *buffer = (uint8_t *) ::mmap (0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
NS_ASSERT_MSG (buffer != MAP_FAILED, "unable to mmap file=" << filename << " error=" << strerror (errno));
close (fd);
struct FileInfo fileInfo = EditBuffer (buffer, selfId);
if (fileInfo.p_vaddr == -1)
{
NS_LOG_UNCOND ("*** unable to open non-shared object file=" << filename << " ***");
NS_ASSERT_MSG (false, "make it sure that DCE binrary file " << filename
<< " was built with correct options: (CFLAGS=-fPIC, LDFLAGS=-pie -rdynamic)");
}
// write back changes to hard disk
retval = ::msync (buffer, size, MS_SYNC);
NS_ASSERT_MSG (retval == 0, "msync failed " << strerror (errno));
retval = ::munmap (buffer, size);
NS_ASSERT_MSG (retval == 0, "munmap failed " << strerror (errno));
return fileInfo;
}
uint32_t
ElfCache::AllocateId (void)
{
static uint32_t id = 0;
id++;
return id;
}
uint32_t
ElfCache::GetDepId (std::string depname) const
{
for (std::vector<struct Overriden>::const_iterator i = m_overriden.begin (); i != m_overriden.end (); ++i)
{
struct Overriden overriden = *i;
if (overriden.from == depname)
{
depname = overriden.to;
}
NS_LOG_DEBUG ("from: " << overriden.from << ", to: " << overriden.to);
}
for (std::vector<struct ElfCachedFile>::const_iterator i = m_files.begin (); i != m_files.end (); ++i)
{
NS_LOG_DEBUG ("cache: " << i->basename);
if (depname == i->basename)
{
return i->id;
}
}
NS_ASSERT_MSG (false, "did not find " << depname);
return 0; // quiet compiler
}
std::string
ElfCache::EnsureCacheDirectory (void) const
{
int retval = ::mkdir (m_directory.c_str (), S_IRWXU);
if (retval == 0)
{
NS_LOG_DEBUG ("Created elf loader cache directory.");
}
std::ostringstream oss;
oss << m_directory << "/" << m_uid;
retval = ::mkdir (oss.str ().c_str (), S_IRWXU);
if (retval == 0)
{
NS_LOG_DEBUG ("Created elf loader cache directory.");
}
return oss.str ();
}
struct ElfCache::ElfCachedFile
ElfCache::Add (std::string filename)
{
NS_LOG_FUNCTION (this << filename);
std::string basename = GetBasename (filename);
// check if we have an override rule for this file
for (std::vector<struct Overriden>::const_iterator i = m_overriden.begin (); i != m_overriden.end (); ++i)
{
struct Overriden overriden = *i;
if (overriden.from == basename)
{
// check if the overriden file is already in-store.
for (std::vector<struct ElfCachedFile>::const_iterator i = m_files.begin (); i != m_files.end (); ++i)
{
if (i->basename == overriden.to)
{
return *i;
}
}
NS_ASSERT (false);
}
}
// check if the file is already in-store.
for (std::vector<struct ElfCachedFile>::const_iterator i = m_files.begin (); i != m_files.end (); ++i)
{
if (i->basename == basename)
{
return *i;
}
}
std::string directory = EnsureCacheDirectory ();
std::string fileCopy = directory + "/" + basename;
CopyFile (filename, fileCopy);
uint32_t selfId = AllocateId ();
struct FileInfo fileInfo = EditFile (fileCopy, selfId);
struct ElfCachedFile cached;
cached.cachedFilename = fileCopy;
cached.basename = basename;
cached.data_p_vaddr = fileInfo.p_vaddr;
cached.data_p_memsz = fileInfo.p_memsz;
cached.id = selfId;
cached.deps = fileInfo.deps;
m_files.push_back (cached);
return cached;
}
} // namespace ns3