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Teach --replace-needed to update .gnu.version_r table #85

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Apr 1, 2016
Merged

Teach --replace-needed to update .gnu.version_r table #85

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25cb97c
Teach --replace-needed to update .gnu.version_r table
njsmith Apr 1, 2016
907c020
Small cleanups to replaceNeeded
njsmith Apr 1, 2016
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65 changes: 59 additions & 6 deletions src/patchelf.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -53,8 +53,8 @@ off_t fileSize, maxSize;
unsigned char * contents = 0;


#define ElfFileParams class Elf_Ehdr, class Elf_Phdr, class Elf_Shdr, class Elf_Addr, class Elf_Off, class Elf_Dyn, class Elf_Sym
#define ElfFileParamNames Elf_Ehdr, Elf_Phdr, Elf_Shdr, Elf_Addr, Elf_Off, Elf_Dyn, Elf_Sym
#define ElfFileParams class Elf_Ehdr, class Elf_Phdr, class Elf_Shdr, class Elf_Addr, class Elf_Off, class Elf_Dyn, class Elf_Sym, class Elf_Verneed
#define ElfFileParamNames Elf_Ehdr, Elf_Phdr, Elf_Shdr, Elf_Addr, Elf_Off, Elf_Dyn, Elf_Sym, Elf_Verneed


static unsigned int getPageSize(){
Expand Down Expand Up @@ -1260,6 +1260,8 @@ void ElfFile<ElfFileParamNames>::replaceNeeded(map<string, string>& libs)

Elf_Dyn * dyn = (Elf_Dyn *) (contents + rdi(shdrDynamic.sh_offset));

unsigned int verNeedNum = 0;

unsigned int dynStrAddedBytes = 0;

for ( ; rdi(dyn->d_tag) != DT_NULL; dyn++) {
Expand All @@ -1272,13 +1274,13 @@ void ElfFile<ElfFileParamNames>::replaceNeeded(map<string, string>& libs)

// technically, the string referred by d_val could be used otherwise, too (although unlikely)
// we'll therefore add a new string
debug("resizing .dynstr ...");
debug("resizing .dynstr ...\n");

string & newDynStr = replaceSection(".dynstr",
rdi(shdrDynStr.sh_size) + replacement.size() + 1 + dynStrAddedBytes);
setSubstr(newDynStr, rdi(shdrDynStr.sh_size) + dynStrAddedBytes, replacement + '\0');

dyn->d_un.d_val = shdrDynStr.sh_size + dynStrAddedBytes;
wri(dyn->d_un.d_val, rdi(shdrDynStr.sh_size) + dynStrAddedBytes);

dynStrAddedBytes += replacement.size() + 1;

Expand All @@ -1287,6 +1289,57 @@ void ElfFile<ElfFileParamNames>::replaceNeeded(map<string, string>& libs)
debug("keeping DT_NEEDED entry `%s'\n", name);
}
}
if (rdi(dyn->d_tag) == DT_VERNEEDNUM) {
verNeedNum = rdi(dyn->d_un.d_val);
}
}

// If a replaced library uses symbol versions, then there will also be
// references to it in the "version needed" table, and these also need to
// be replaced.

if (verNeedNum) {
Elf_Shdr & shdrVersionR = findSection(".gnu.version_r");
// The filename strings in the .gnu.version_r are different from the
// ones in .dynamic: instead of being in .dynstr, they're in some
// arbitrary section and we have to look in ->sh_link to figure out
// which one.
Elf_Shdr & shdrVersionRStrings = shdrs[rdi(shdrVersionR.sh_link)];
// this is where we find the actual filename strings
char * verStrTab = (char *) contents + rdi(shdrVersionRStrings.sh_offset);
// and we also need the name of the section containing the strings, so
// that we can pass it to replaceSection
string versionRStringsSName = getSectionName(shdrVersionRStrings);

debug("found .gnu.version_r with %i entries, strings in %s\n", verNeedNum, versionRStringsSName.c_str());

unsigned int verStrAddedBytes = 0;

Elf_Verneed * need = (Elf_Verneed *) (contents + rdi(shdrVersionR.sh_offset));
while (verNeedNum > 0) {
char * file = verStrTab + rdi(need->vn_file);
if (libs.find(file) != libs.end()) {
const string & replacement = libs[file];

debug("replacing .gnu.version_r entry `%s' with `%s'\n", file, replacement.c_str());
debug("resizing string section %s ...\n", versionRStringsSName.c_str());

string & newVerDynStr = replaceSection(versionRStringsSName,
rdi(shdrVersionRStrings.sh_size) + replacement.size() + 1 + verStrAddedBytes);
setSubstr(newVerDynStr, rdi(shdrVersionRStrings.sh_size) + verStrAddedBytes, replacement + '\0');

wri(need->vn_file, rdi(shdrVersionRStrings.sh_size) + verStrAddedBytes);

verStrAddedBytes += replacement.size() + 1;

changed = true;
} else {
debug("keeping .gnu.version_r entry `%s'\n", file);
}
// the Elf_Verneed structures form a linked list, so jump to next entry
need = (Elf_Verneed *) (contents + rdi(shdrVersionR.sh_offset) + rdi(need->vn_next));
--verNeedNum;
}
}
}

Expand Down Expand Up @@ -1474,13 +1527,13 @@ static void patchElf()
if (contents[EI_CLASS] == ELFCLASS32 &&
contents[EI_VERSION] == EV_CURRENT)
{
ElfFile<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr, Elf32_Addr, Elf32_Off, Elf32_Dyn, Elf32_Sym> elfFile;
ElfFile<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr, Elf32_Addr, Elf32_Off, Elf32_Dyn, Elf32_Sym, Elf32_Verneed> elfFile;
patchElf2(elfFile);
}
else if (contents[EI_CLASS] == ELFCLASS64 &&
contents[EI_VERSION] == EV_CURRENT)
{
ElfFile<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr, Elf64_Addr, Elf64_Off, Elf64_Dyn, Elf64_Sym> elfFile;
ElfFile<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr, Elf64_Addr, Elf64_Off, Elf64_Dyn, Elf64_Sym, Elf64_Verneed> elfFile;
patchElf2(elfFile);
}
else {
Expand Down