Author: eelco
Date: Sun Sep 11 20:10:14 2011
New Revision: 29192
URL: https://ssl.nixos.org/websvn/nix/?rev=29192&sc=1
Log:
* Support executables created by the Gold linker (NixOS/140). These
are marked as ET_DYN (not ET_EXEC) and have a starting virtual
address of 0 so they cannot grow downwards. In order not to run
into a Linux kernel bug, the virtual address and the offset of the
new PT_LOAD segment have to be equal; otherwise ld-linux segfaults.
To ensure this, it may be necessary to add some padding to the
executable (potentially a lot of padding, if the executable has a
large uninitialised data segment).
* Use size_t rather than off_t in some places.
Modified:
patchelf/trunk/src/patchelf.cc
Modified: patchelf/trunk/src/patchelf.cc
==============================================================================
--- patchelf/trunk/src/patchelf.cc Sun Sep 11 18:58:24 2011 (r29191)
+++ patchelf/trunk/src/patchelf.cc Sun Sep 11 20:10:14 2011 (r29192)
@@ -55,6 +55,8 @@
bool changed;
+ bool isExecutable;
+
typedef string SectionName;
typedef map<SectionName, string> ReplacedSections;
@@ -245,6 +247,8 @@
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::parse()
{
+ isExecutable = false;
+
/* Check the ELF header for basic validity. */
if (fileSize < (off_t) sizeof(Elf_Ehdr)) error("missing ELF header");
@@ -268,8 +272,10 @@
error("program headers have wrong size");
/* Copy the program and section headers. */
- for (int i = 0; i < rdi(hdr->e_phnum); ++i)
+ for (int i = 0; i < rdi(hdr->e_phnum); ++i) {
phdrs.push_back(* ((Elf_Phdr *) (contents + rdi(hdr->e_phoff)) + i));
+ if (rdi(phdrs[i].p_type) == PT_INTERP) isExecutable = true;
+ }
for (int i = 0; i < rdi(hdr->e_shnum); ++i)
shdrs.push_back(* ((Elf_Shdr *) (contents + rdi(hdr->e_shoff)) + i));
@@ -486,7 +492,7 @@
{
string sectionName = i->first;
Elf_Shdr & shdr = findSection(sectionName);
- debug("rewriting section `%s' from offset %d (size %d) to offset %d
(size %d)\n",
+ debug("rewriting section `%s' from offset 0x%x (size %d) to offset
0x%x (size %d)\n",
sectionName.c_str(), rdi(shdr.sh_offset), rdi(shdr.sh_size),
curOff, i->second.size());
memcpy(contents + curOff, (unsigned char *) i->second.c_str(),
@@ -552,11 +558,40 @@
debug("needed space is %d\n", neededSpace);
- off_t startOffset = roundUp(fileSize, pageSize);
+ size_t startOffset = roundUp(fileSize, pageSize);
growFile(startOffset + neededSpace);
+ /* Even though this file is of type ET_DYN, it could actually be
+ an executable. For instance, Gold produces executables marked
+ ET_DYN. In that case we can still hit the kernel bug that
+ necessitated rewriteSectionsExecutable(). However, such
+ executables also tend to start at virtual address 0, so
+ rewriteSectionsExecutable() won't work because it doesn't have
+ any virtual address space to grow downwards into. As a
+ workaround, make sure that the virtual address of our new
+ PT_LOAD segment relative to the first PT_LOAD segment is equal
+ to its offset; otherwise we hit the kernel bug. This may
+ require creating a hole in the executable. The bigger the size
+ of the uninitialised data segment, the bigger the hole. */
+ if (isExecutable) {
+ if (startOffset >= startPage) {
+ debug("shifting new PT_LOAD segment by %d bytes to work around a
Linux kernel bug\n", startOffset - startPage);
+ } else {
+ size_t hole = startPage - startOffset;
+ /* Print a warning, because the hole could be very big. */
+ fprintf(stderr, "warning: working around a Linux kernel bug by
creating a hole of %zu bytes in ‘%s’\n", hole, fileName.c_str());
+ assert(hole % pageSize == 0);
+ /* !!! We could create an actual hole in the file here,
+ but it's probably not worth the effort. */
+ growFile(fileSize + hole);
+ startOffset += hole;
+ }
+ startPage = startOffset;
+ }
+
+
/* Add a segment that maps the replaced sections and program
headers into memory. */
phdrs.resize(rdi(hdr->e_phnum) + 1);
@@ -610,7 +645,7 @@
SHT_PROGBITS). These cannot be moved in virtual address space
since that would invalidate absolute references to them. */
assert(lastReplaced + 1 < shdrs.size()); /* !!! I'm lazy. */
- off_t startOffset = rdi(shdrs[lastReplaced + 1].sh_offset);
+ size_t startOffset = rdi(shdrs[lastReplaced + 1].sh_offset);
Elf_Addr startAddr = rdi(shdrs[lastReplaced + 1].sh_addr);
string prevSection;
for (unsigned int i = 1; i <= lastReplaced; ++i) {
@@ -651,7 +686,7 @@
/* Compute the total space needed for the replaced sections, the
ELF header, and the program headers. */
- off_t neededSpace = sizeof(Elf_Ehdr) + phdrs.size() * sizeof(Elf_Phdr);
+ size_t neededSpace = sizeof(Elf_Ehdr) + phdrs.size() * sizeof(Elf_Phdr);
for (ReplacedSections::iterator i = replacedSections.begin();
i != replacedSections.end(); ++i)
neededSpace += roundUp(i->second.size(), sectionAlignment);
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