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Merge pull request #261 from pcc/fix3

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Compute base addresses from program headers while reading /proc/self/maps.
This commit is contained in:
Fumitoshi Ukai 2017-11-10 16:55:27 +09:00 committed by GitHub
commit 2063b38708
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2 changed files with 71 additions and 53 deletions
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13
Makefile.am
View File

@ -63,7 +63,10 @@ TEST_LIBS = $(GTEST_LIBS) $(GMOCK_LIBS) $(GFLAGS_LIBS)
## TESTS_ENVIRONMENT sets environment variables for when you run unittest,
## but it only seems to take effect for *binary* unittests (argh!)
TESTS =
TESTS_ENVIRONMENT =
# Set a small stack size so that (at least on Linux) PIEs are mapped at a lower
# address than DSOs. This is used by symbolize_pie_unittest to check that we can
# successfully symbolize PIEs loaded at low addresses.
TESTS_ENVIRONMENT = ulimit -s 8192;
check_SCRIPTS =
# Every time you add a unittest to check_SCRIPTS, add it here too
noinst_SCRIPTS =
@ -145,6 +148,14 @@ symbolize_unittest_CXXFLAGS = $(PTHREAD_CFLAGS) $(TEST_CFLAGS)
symbolize_unittest_LDFLAGS = $(PTHREAD_CFLAGS)
symbolize_unittest_LDADD = libglog.la $(COMMON_LIBS) $(TEST_LIBS)
TESTS += symbolize_pie_unittest
symbolize_pie_unittest_SOURCES = $(gloginclude_HEADERS) \
src/symbolize_unittest.cc
nodist_symbolize_pie_unittest_SOURCES = $(nodist_gloginclude_HEADERS)
symbolize_pie_unittest_CXXFLAGS = $(PTHREAD_CFLAGS) $(TEST_CFLAGS) -fPIE
symbolize_pie_unittest_LDFLAGS = $(PTHREAD_CFLAGS) -pie
symbolize_pie_unittest_LDADD = libglog.la $(COMMON_LIBS) $(TEST_LIBS)
TESTS += stl_logging_unittest
stl_logging_unittest_SOURCES = $(gloginclude_HEADERS) \
src/stl_logging_unittest.cc

111
src/symbolize.cc
View File

@ -56,6 +56,8 @@
#if defined(HAVE_SYMBOLIZE)
#include <string.h>
#include <limits>
#include "symbolize.h"
@ -325,41 +327,17 @@ FindSymbol(uint64_t pc, const int fd, char *out, int out_size,
// both regular and dynamic symbol tables if necessary. On success,
// write the symbol name to "out" and return true. Otherwise, return
// false.
static bool GetSymbolFromObjectFile(const int fd, uint64_t pc,
char *out, int out_size,
uint64_t map_base_address) {
static bool GetSymbolFromObjectFile(const int fd,
uint64_t pc,
char* out,
int out_size,
uint64_t base_address) {
// Read the ELF header.
ElfW(Ehdr) elf_header;
if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
return false;
}
uint64_t symbol_offset = 0;
if (elf_header.e_type == ET_DYN) { // DSO needs offset adjustment.
ElfW(Phdr) phdr;
// We need to find the PT_LOAD segment corresponding to the read-execute
// file mapping in order to correctly perform the offset adjustment.
for (unsigned i = 0; i != elf_header.e_phnum; ++i) {
if (!ReadFromOffsetExact(fd, &phdr, sizeof(phdr),
elf_header.e_phoff + i * sizeof(phdr)))
return false;
if (phdr.p_type == PT_LOAD &&
(phdr.p_flags & (PF_R | PF_X)) == (PF_R | PF_X)) {
// Find the mapped address corresponding to virtual address zero. We do
// this by first adding p_offset. This gives us the mapped address of
// the start of the segment, or in other words the mapped address
// corresponding to the virtual address of the segment. (Note that this
// is distinct from the start address, as p_offset is not guaranteed to
// be page aligned.) We then subtract p_vaddr, which takes us to virtual
// address zero.
symbol_offset = map_base_address + phdr.p_offset - phdr.p_vaddr;
break;
}
}
if (symbol_offset == 0)
return false;
}
ElfW(Shdr) symtab, strtab;
// Consult a regular symbol table first.
@ -369,8 +347,7 @@ static bool GetSymbolFromObjectFile(const int fd, uint64_t pc,
symtab.sh_link * sizeof(symtab))) {
return false;
}
if (FindSymbol(pc, fd, out, out_size, symbol_offset,
&strtab, &symtab)) {
if (FindSymbol(pc, fd, out, out_size, base_address, &strtab, &symtab)) {
return true; // Found the symbol in a regular symbol table.
}
}
@ -382,8 +359,7 @@ static bool GetSymbolFromObjectFile(const int fd, uint64_t pc,
symtab.sh_link * sizeof(symtab))) {
return false;
}
if (FindSymbol(pc, fd, out, out_size, symbol_offset,
&strtab, &symtab)) {
if (FindSymbol(pc, fd, out, out_size, base_address, &strtab, &symtab)) {
return true; // Found the symbol in a dynamic symbol table.
}
}
@ -532,7 +508,6 @@ OpenObjectFileContainingPcAndGetStartAddress(uint64_t pc,
int out_file_name_size) {
int object_fd;
// Open /proc/self/maps.
int maps_fd;
NO_INTR(maps_fd = open("/proc/self/maps", O_RDONLY));
FileDescriptor wrapped_maps_fd(maps_fd);
@ -540,6 +515,13 @@ OpenObjectFileContainingPcAndGetStartAddress(uint64_t pc,
return -1;
}
int mem_fd;
NO_INTR(mem_fd = open("/proc/self/mem", O_RDONLY));
FileDescriptor wrapped_mem_fd(mem_fd);
if (wrapped_mem_fd.get() < 0) {
return -1;
}
// Iterate over maps and look for the map containing the pc. Then
// look into the symbol tables inside.
char buf[1024]; // Big enough for line of sane /proc/self/maps
@ -575,11 +557,6 @@ OpenObjectFileContainingPcAndGetStartAddress(uint64_t pc,
}
++cursor; // Skip ' '.
// Check start and end addresses.
if (!(start_address <= pc && pc < end_address)) {
continue; // We skip this map. PC isn't in this map.
}
// Read flags. Skip flags until we encounter a space or eol.
const char * const flags_start = cursor;
while (cursor < eol && *cursor != ' ') {
@ -590,6 +567,49 @@ OpenObjectFileContainingPcAndGetStartAddress(uint64_t pc,
return -1; // Malformed line.
}
// Determine the base address by reading ELF headers in process memory.
ElfW(Ehdr) ehdr;
// Skip non-readable maps.
if (flags_start[0] == 'r' &&
ReadFromOffsetExact(mem_fd, &ehdr, sizeof(ElfW(Ehdr)), start_address) &&
memcmp(ehdr.e_ident, ELFMAG, SELFMAG) == 0) {
switch (ehdr.e_type) {
case ET_EXEC:
base_address = 0;
break;
case ET_DYN:
// Find the segment containing file offset 0. This will correspond
// to the ELF header that we just read. Normally this will have
// virtual address 0, but this is not guaranteed. We must subtract
// the virtual address from the address where the ELF header was
// mapped to get the base address.
//
// If we fail to find a segment for file offset 0, use the address
// of the ELF header as the base address.
base_address = start_address;
for (unsigned i = 0; i != ehdr.e_phnum; ++i) {
ElfW(Phdr) phdr;
if (ReadFromOffsetExact(
mem_fd, &phdr, sizeof(phdr),
start_address + ehdr.e_phoff + i * sizeof(phdr)) &&
phdr.p_type == PT_LOAD && phdr.p_offset == 0) {
base_address = start_address - phdr.p_vaddr;
break;
}
}
break;
default:
// ET_REL or ET_CORE. These aren't directly executable, so they don't
// affect the base address.
break;
}
}
// Check start and end addresses.
if (!(start_address <= pc && pc < end_address)) {
continue; // We skip this map. PC isn't in this map.
}
// Check flags. We are only interested in "r*x" maps.
if (flags_start[0] != 'r' || flags_start[2] != 'x') {
continue; // We skip this map.
@ -604,19 +624,6 @@ OpenObjectFileContainingPcAndGetStartAddress(uint64_t pc,
}
++cursor; // Skip ' '.
// Don't subtract 'start_address' from the first entry:
// * If a binary is compiled w/o -pie, then the first entry in
// process maps is likely the binary itself (all dynamic libs
// are mapped higher in address space). For such a binary,
// instruction offset in binary coincides with the actual
// instruction address in virtual memory (as code section
// is mapped to a fixed memory range).
// * If a binary is compiled with -pie, all the modules are
// mapped high at address space (in particular, higher than
// shadow memory of the tool), so the module can't be the
// first entry.
base_address = ((num_maps == 1) ? 0U : start_address) - file_offset;
// Skip to file name. "cursor" now points to dev. We need to
// skip at least two spaces for dev and inode.
int num_spaces = 0;