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dumpwriterelf.cpp
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dumpwriterelf.cpp
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
#include "createdump.h"
extern int g_readProcessMemoryErrno;
// Write the core dump file:
// ELF header
// Single section header (Shdr) for 64 bit program header count
// Phdr for the PT_NOTE
// PT_LOAD
// PT_NOTEs
// process info (prpsinfo_t)
// NT_FILE entries
// threads
// alignment
// memory blocks
bool
DumpWriter::WriteDump()
{
// Write the ELF header
Ehdr ehdr;
memset(&ehdr, 0, sizeof(Ehdr));
ehdr.e_ident[0] = ELFMAG0;
ehdr.e_ident[1] = ELFMAG1;
ehdr.e_ident[2] = ELFMAG2;
ehdr.e_ident[3] = ELFMAG3;
ehdr.e_ident[EI_CLASS] = ELF_CLASS;
ehdr.e_ident[EI_DATA] = ELFDATA2LSB;
ehdr.e_ident[EI_VERSION] = EV_CURRENT;
ehdr.e_ident[EI_OSABI] = ELFOSABI_LINUX;
ehdr.e_type = ET_CORE;
ehdr.e_machine = ELF_ARCH;
ehdr.e_version = EV_CURRENT;
ehdr.e_phoff = sizeof(Ehdr);
ehdr.e_ehsize = sizeof(Ehdr);
ehdr.e_phentsize = sizeof(Phdr);
// The ELF header only allows UINT16 for the number of program
// headers. In a core dump this equates to PT_NODE and PT_LOAD.
//
// When more program headers than 65534 the first section entry
// is used to store the actual program header count.
// PT_NOTE + number of memory regions
uint64_t phnum = 1;
for (const MemoryRegion& memoryRegion : m_crashInfo.MemoryRegions())
{
phnum++;
}
if (phnum < PH_HDR_CANARY) {
ehdr.e_phnum = phnum;
}
else {
ehdr.e_phnum = PH_HDR_CANARY;
ehdr.e_phoff = sizeof(Ehdr) + sizeof(Shdr);
ehdr.e_shnum = 1;
ehdr.e_shoff = sizeof(Ehdr);
ehdr.e_shentsize = sizeof(Shdr);
}
if (!WriteData(&ehdr, sizeof(Ehdr))) {
return false;
}
size_t offset = sizeof(Ehdr) + (phnum * sizeof(Phdr));
size_t filesz = GetProcessInfoSize() + GetAuxvInfoSize() + GetThreadInfoSize() + GetNTFileInfoSize();
if (ehdr.e_phnum == PH_HDR_CANARY)
{
// Add single section containing the actual count of the program headers to be written.
Shdr shdr;
memset(&shdr, 0, sizeof(shdr));
shdr.sh_info = phnum;
shdr.sh_size = 1;
offset += sizeof(Shdr);
// When section header offset is present but ehdr section num = 0 then it is expected that
// the sh_size indicates the size of the section array or 1 in our case.
if (!WriteData(&shdr, sizeof(shdr))) {
return false;
}
}
// PT_NOTE header
Phdr phdr;
memset(&phdr, 0, sizeof(Phdr));
phdr.p_type = PT_NOTE;
phdr.p_offset = offset;
phdr.p_filesz = filesz;
if (!WriteData(&phdr, sizeof(phdr))) {
return false;
}
// PT_NOTE sections must end on 4 byte boundary
// We output the NT_FILE, AUX and Thread entries
// AUX is aligned, NT_FILE is aligned and then we
// check to pad end of the thread list
phdr.p_type = PT_LOAD;
phdr.p_align = 4096;
size_t finalNoteAlignment = phdr.p_align - ((offset + filesz) % phdr.p_align);
if (finalNoteAlignment == phdr.p_align) {
finalNoteAlignment = 0;
}
offset += finalNoteAlignment;
TRACE("Writing memory region headers to core file\n");
// Write memory region note headers
for (const MemoryRegion& memoryRegion : m_crashInfo.MemoryRegions())
{
phdr.p_flags = memoryRegion.Permissions();
phdr.p_vaddr = memoryRegion.StartAddress();
phdr.p_memsz = memoryRegion.Size();
offset += filesz;
phdr.p_filesz = filesz = memoryRegion.Size();
phdr.p_offset = offset;
if (!WriteData(&phdr, sizeof(phdr))) {
return false;
}
}
// Write process info data to core file
if (!WriteProcessInfo()) {
return false;
}
// Write auxv data to core file
if (!WriteAuxv()) {
return false;
}
// Write NT_FILE entries to the core file
if (!WriteNTFileInfo()) {
return false;
}
TRACE("Writing %zd thread entries to core file\n", m_crashInfo.Threads().size());
// Write all the thread's state and registers
for (const ThreadInfo* thread : m_crashInfo.Threads())
{
if (!WriteThread(*thread)) {
return false;
}
}
// Zero out the end of the PT_NOTE section to the boundary
// and then laydown the memory blocks
if (finalNoteAlignment > 0) {
if (finalNoteAlignment > sizeof(m_tempBuffer)) {
printf_error("Internal error: finalNoteAlignment %zu > sizeof(m_tempBuffer)\n", finalNoteAlignment);
return false;
}
memset(m_tempBuffer, 0, finalNoteAlignment);
if (!WriteData(m_tempBuffer, finalNoteAlignment)) {
return false;
}
}
TRACE("Writing %" PRIu64 " memory regions to core file\n", phnum - 1);
// Read from target process and write memory regions to core
uint64_t total = 0;
for (const MemoryRegion& memoryRegion : m_crashInfo.MemoryRegions())
{
uint64_t address = memoryRegion.StartAddress();
size_t size = memoryRegion.Size();
total += size;
if (address == SpecialDiagInfoAddress)
{
if (!WriteDiagInfo(size)) {
return false;
}
}
else
{
while (size > 0)
{
size_t bytesToRead = std::min(size, sizeof(m_tempBuffer));
size_t read = 0;
if (!m_crashInfo.ReadProcessMemory((void*)address, m_tempBuffer, bytesToRead, &read)) {
printf_error("Error reading memory at %" PRIA PRIx64 " size %08zx FAILED %s (%d)\n", address, bytesToRead, strerror(g_readProcessMemoryErrno), g_readProcessMemoryErrno);
return false;
}
// This can happen if the target process dies before createdump is finished
if (read == 0) {
printf_error("Error reading memory at %" PRIA PRIx64 " size %08zx returned 0 bytes read: %s (%d)\n", address, bytesToRead, strerror(g_readProcessMemoryErrno), g_readProcessMemoryErrno);
return false;
}
if (!WriteData(m_tempBuffer, read)) {
return false;
}
address += read;
size -= read;
}
}
}
printf_status("Written %" PRId64 " bytes (%" PRId64 " pages) to core file\n", total, total / PAGE_SIZE);
return true;
}
bool
DumpWriter::WriteProcessInfo()
{
prpsinfo_t processInfo;
memset(&processInfo, 0, sizeof(processInfo));
processInfo.pr_sname = 'R';
processInfo.pr_pid = m_crashInfo.Pid();
processInfo.pr_ppid = m_crashInfo.Ppid();
processInfo.pr_pgrp = m_crashInfo.Tgid();
m_crashInfo.Name().copy(processInfo.pr_fname, sizeof(processInfo.pr_fname));
Nhdr nhdr;
memset(&nhdr, 0, sizeof(nhdr));
nhdr.n_namesz = 5;
nhdr.n_descsz = sizeof(prpsinfo_t);
nhdr.n_type = NT_PRPSINFO;
TRACE("Writing process information to core file\n");
// Write process info data to core file
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("CORE\0PRP", 8) ||
!WriteData(&processInfo, sizeof(prpsinfo_t))) {
return false;
}
return true;
}
bool
DumpWriter::WriteAuxv()
{
Nhdr nhdr;
memset(&nhdr, 0, sizeof(nhdr));
nhdr.n_namesz = 5;
nhdr.n_descsz = m_crashInfo.GetAuxvSize();
nhdr.n_type = NT_AUXV;
TRACE("Writing %zd auxv entries to core file\n", m_crashInfo.AuxvEntries().size());
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("CORE\0AUX", 8)) {
return false;
}
for (const auto& auxvEntry : m_crashInfo.AuxvEntries())
{
if (!WriteData(&auxvEntry, sizeof(auxvEntry))) {
return false;
}
}
return true;
}
struct NTFileEntry
{
unsigned long StartAddress;
unsigned long EndAddress;
unsigned long Offset;
};
// Calculate the NT_FILE entries total size
size_t
DumpWriter::GetNTFileInfoSize(size_t* alignmentBytes)
{
size_t count = m_crashInfo.ModuleMappings().size();
size_t size = 0;
// Header, CORE, entry count, page size
size = sizeof(Nhdr) + 8 + sizeof(count) + sizeof(size);
// start_address, end_address, offset
size += count * sizeof(NTFileEntry);
// \0 terminator for each filename
size += count;
// File name storage needed
for (const MemoryRegion& image : m_crashInfo.ModuleMappings()) {
size += image.FileName().length();
}
// Notes must end on 4 byte alignment
size_t alignmentBytesNeeded = 4 - (size % 4);
size += alignmentBytesNeeded;
if (alignmentBytes != nullptr) {
*alignmentBytes = alignmentBytesNeeded;
}
return size;
}
// Write NT_FILE entries to the PT_NODE section
//
// Nhdr (NT_FILE)
// Total entries
// Page size
// [0] start_address end_address offset
// [1] start_address end_address offset
// [file name]\0[file name]\0...
bool
DumpWriter::WriteNTFileInfo()
{
Nhdr nhdr;
memset(&nhdr, 0, sizeof(nhdr));
// CORE + \0 and we align on 4 byte boundary
// so we can use CORE\0FIL for easier hex debugging
nhdr.n_namesz = 5;
nhdr.n_type = NT_FILE; // "FILE"
// Size of payload for NT_FILE after CORE tag written
size_t alignmentBytesNeeded = 0;
nhdr.n_descsz = GetNTFileInfoSize(&alignmentBytesNeeded) - sizeof(nhdr) - 8;
size_t count = m_crashInfo.ModuleMappings().size();
size_t pageSize = PAGE_SIZE;
TRACE("Writing %zd NT_FILE entries to core file\n", m_crashInfo.ModuleMappings().size());
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("CORE\0FIL", 8) ||
!WriteData(&count, sizeof(count)) ||
!WriteData(&pageSize, sizeof(pageSize))) {
return false;
}
for (const MemoryRegion& image : m_crashInfo.ModuleMappings())
{
struct NTFileEntry entry { (unsigned long)image.StartAddress(), (unsigned long)image.EndAddress(), (unsigned long)(image.Offset() / pageSize) };
if (!WriteData(&entry, sizeof(entry))) {
return false;
}
}
for (const MemoryRegion& image : m_crashInfo.ModuleMappings())
{
if (!WriteData(image.FileName().c_str(), image.FileName().length()) ||
!WriteData("\0", 1)) {
return false;
}
}
// Has to end on a 4 byte boundary. Debugger, readelf and such
// will automatically align on next 4 bytes and look for a PT_NOTE
// header.
if (alignmentBytesNeeded) {
if (!WriteData("\0\0\0\0", alignmentBytesNeeded)) {
return false;
}
}
return true;
}
bool
DumpWriter::WriteThread(const ThreadInfo& thread)
{
prstatus_t pr;
memset(&pr, 0, sizeof(pr));
const siginfo_t* siginfo = nullptr;
if (m_crashInfo.Signal() != 0 && thread.IsCrashThread())
{
siginfo = m_crashInfo.SigInfo();
pr.pr_info.si_signo = siginfo->si_signo;
pr.pr_info.si_code = siginfo->si_code;
pr.pr_info.si_errno = siginfo->si_errno;
pr.pr_cursig = siginfo->si_signo;
}
pr.pr_pid = thread.Tid();
pr.pr_ppid = thread.Ppid();
pr.pr_pgrp = thread.Tgid();
memcpy(&pr.pr_reg, thread.GPRegisters(), sizeof(user_regs_struct));
Nhdr nhdr;
memset(&nhdr, 0, sizeof(nhdr));
// Name size is CORE plus the NULL terminator
// The format requires 4 byte alignment so the
// value written in 8 bytes. Stuff the last 3
// bytes with the type of NT_PRSTATUS so it is
// easier to debug in a hex editor.
nhdr.n_namesz = 5;
nhdr.n_descsz = sizeof(prstatus_t);
nhdr.n_type = NT_PRSTATUS;
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("CORE\0THR", 8) ||
!WriteData(&pr, sizeof(prstatus_t))) {
return false;
}
nhdr.n_descsz = sizeof(user_fpregs_struct);
nhdr.n_type = NT_FPREGSET;
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("CORE\0FLT", 8) ||
!WriteData(thread.FPRegisters(), sizeof(user_fpregs_struct))) {
return false;
}
#if defined(__i386__)
nhdr.n_namesz = 6;
nhdr.n_descsz = sizeof(user_fpxregs_struct);
nhdr.n_type = NT_PRXFPREG;
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("LINUX\0\0\0", 8) ||
!WriteData(thread.FPXRegisters(), sizeof(user_fpxregs_struct))) {
return false;
}
#endif
#if defined(__arm__) && defined(__VFP_FP__) && !defined(__SOFTFP__)
nhdr.n_namesz = 6;
nhdr.n_descsz = sizeof(user_vfpregs_struct);
nhdr.n_type = NT_ARM_VFP;
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("LINUX\0\0\0", 8) ||
!WriteData(thread.VFPRegisters(), sizeof(user_vfpregs_struct))) {
return false;
}
#endif
if (siginfo != nullptr)
{
TRACE("Writing NT_SIGINFO tid %04x signo %d (%04x) code %04x errno %04x addr %p\n",
thread.Tid(), siginfo->si_signo, siginfo->si_signo, siginfo->si_code, siginfo->si_errno, siginfo->si_addr);
nhdr.n_namesz = 5;
nhdr.n_descsz = sizeof(siginfo_t);
nhdr.n_type = NT_SIGINFO;
if (!WriteData(&nhdr, sizeof(nhdr)) ||
!WriteData("CORE\0SIG", 8) ||
!WriteData(siginfo, sizeof(siginfo_t))) {
return false;
}
}
return true;
}