ClickHouse/base/common/getResource.cpp
2021-06-11 14:35:40 -07:00

46 lines
2.0 KiB
C++

#include "getResource.h"
#include "unaligned.h"
#include <dlfcn.h>
#include <string>
#include <boost/algorithm/string/replace.hpp>
std::string_view getResource(std::string_view name)
{
// Convert the resource file name into the form generated by `ld -r -b binary`.
std::string name_replaced(name);
std::replace(name_replaced.begin(), name_replaced.end(), '/', '_');
std::replace(name_replaced.begin(), name_replaced.end(), '-', '_');
std::replace(name_replaced.begin(), name_replaced.end(), '.', '_');
boost::replace_all(name_replaced, "+", "_PLUS_");
// In most `dlsym(3)` APIs, one passes the symbol name as it appears via
// something like `nm` or `objdump -t`. For example, a symbol `_foo` would be
// looked up with the string `"_foo"`.
//
// Apple's linker is confusingly different. The NOTES on the man page for
// `dlsym(3)` claim that one looks up the symbol with "the name used in C
// source code". In this example, that would mean using the string `"foo"`.
// This apparently applies even in the case where the symbol did not originate
// from C source, such as the embedded binary resource files used here. So
// the symbol name must not have a leading `_` on Apple platforms. It's not
// clear how this applies to other symbols, such as those which _have_ a leading
// underscore in them by design, many leading underscores, etc.
#if defined OS_DARWIN
std::string prefix = "binary_";
#else
std::string prefix = "_binary_";
#endif
std::string symbol_name_start = prefix + name_replaced + "_start";
std::string symbol_name_end = prefix + name_replaced + "_end";
const char* sym_start = reinterpret_cast<const char*>(dlsym(RTLD_DEFAULT, symbol_name_start.c_str()));
const char* sym_end = reinterpret_cast<const char*>(dlsym(RTLD_DEFAULT, symbol_name_end.c_str()));
if (sym_start && sym_end)
{
auto resource_size = static_cast<size_t>(std::distance(sym_start, sym_end));
return { sym_start, resource_size };
}
return {};
}