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bpf_module_rw_engine.cc
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bpf_module_rw_engine.cc
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/*
* Copyright (c) 2015 PLUMgrid, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http:https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <map>
#include <string>
#include <vector>
#include <llvm/ExecutionEngine/MCJIT.h>
#include <llvm/IR/IRBuilder.h>
#include <llvm/Support/TargetSelect.h>
#include "common.h"
#include "bpf_module.h"
#include "table_storage.h"
namespace ebpf {
using std::map;
using std::move;
using std::string;
using std::unique_ptr;
using std::vector;
using namespace llvm;
bool bpf_module_rw_engine_enabled(void) {
return true;
}
void BPFModule::initialize_rw_engine() {
InitializeNativeTarget();
InitializeNativeTargetAsmPrinter();
}
void BPFModule::cleanup_rw_engine() {
rw_engine_.reset();
}
static LoadInst *createLoad(IRBuilder<> &B, Value *addr, bool isVolatile = false)
{
#if LLVM_VERSION_MAJOR >= 15
if (isa<AllocaInst>(addr))
return B.CreateLoad(dyn_cast<AllocaInst>(addr)->getAllocatedType(), addr, isVolatile);
else
return B.CreateLoad(addr->getType(), addr, isVolatile);
#elif LLVM_VERSION_MAJOR >= 13
return B.CreateLoad(addr->getType()->getPointerElementType(), addr, isVolatile);
#else
return B.CreateLoad(addr, isVolatile);
#endif
}
static Value *createInBoundsGEP(IRBuilder<> &B, Value *ptr, ArrayRef<Value *>idxlist)
{
#if LLVM_VERSION_MAJOR >= 15
if (isa<GlobalValue>(ptr))
return B.CreateInBoundsGEP(dyn_cast<GlobalValue>(ptr)->getValueType(), ptr, idxlist);
else
return B.CreateInBoundsGEP(ptr->getType(), ptr, idxlist);
#elif LLVM_VERSION_MAJOR >= 13
return B.CreateInBoundsGEP(ptr->getType()->getScalarType()->getPointerElementType(),
ptr, idxlist);
#else
return B.CreateInBoundsGEP(ptr, idxlist);
#endif
}
static void debug_printf(Module *mod, IRBuilder<> &B, const string &fmt, vector<Value *> args) {
GlobalVariable *fmt_gvar = B.CreateGlobalString(fmt, "fmt");
args.insert(args.begin(), createInBoundsGEP(B, fmt_gvar, vector<Value *>({B.getInt64(0), B.getInt64(0)})));
args.insert(args.begin(), B.getInt64((uintptr_t)stderr));
Function *fprintf_fn = mod->getFunction("fprintf");
if (!fprintf_fn) {
#if LLVM_VERSION_MAJOR >= 18
vector<Type *> fprintf_fn_args({B.getInt64Ty(), B.getPtrTy()});
#else
vector<Type *> fprintf_fn_args({B.getInt64Ty(), B.getInt8PtrTy()});
#endif
FunctionType *fprintf_fn_type = FunctionType::get(B.getInt32Ty(), fprintf_fn_args, /*isvarArg=*/true);
fprintf_fn = Function::Create(fprintf_fn_type, GlobalValue::ExternalLinkage, "fprintf", mod);
fprintf_fn->setCallingConv(CallingConv::C);
fprintf_fn->addFnAttr(Attribute::NoUnwind);
}
B.CreateCall(fprintf_fn, args);
}
static void finish_sscanf(IRBuilder<> &B, vector<Value *> *args, string *fmt,
const map<string, Value *> &locals, bool exact_args) {
// fmt += "%n";
// int nread = 0;
// int n = sscanf(s, fmt, args..., &nread);
// if (n < 0) return -1;
// s = &s[nread];
Value *sptr = locals.at("sptr");
Value *nread = locals.at("nread");
Function *cur_fn = B.GetInsertBlock()->getParent();
Function *sscanf_fn = B.GetInsertBlock()->getModule()->getFunction("sscanf");
*fmt += "%n";
B.CreateStore(B.getInt32(0), nread);
GlobalVariable *fmt_gvar = B.CreateGlobalString(*fmt, "fmt");
(*args)[1] = createInBoundsGEP(B, fmt_gvar, {B.getInt64(0), B.getInt64(0)});
(*args)[0] = createLoad(B, sptr);
args->push_back(nread);
CallInst *call = B.CreateCall(sscanf_fn, *args);
call->setTailCall(true);
BasicBlock *label_true = BasicBlock::Create(B.getContext(), "", cur_fn);
BasicBlock *label_false = BasicBlock::Create(B.getContext(), "", cur_fn);
// exact_args means fail if don't consume exact number of "%" inputs
// exact_args is disabled for string parsing (empty case)
Value *cond = exact_args ? B.CreateICmpNE(call, B.getInt32(args->size() - 3))
: B.CreateICmpSLT(call, B.getInt32(0));
B.CreateCondBr(cond, label_true, label_false);
B.SetInsertPoint(label_true);
B.CreateRet(B.getInt32(-1));
B.SetInsertPoint(label_false);
// s = &s[nread];
#if LLVM_VERSION_MAJOR >= 15
// cast `sptr` from `ptr`(an opaque pointer rather than `i8*`) to `i8`, so that
// CreateInBoundsGEP can work properly, i.e. the offset is in bytes not in pointer-size
B.CreateStore(
B.CreateInBoundsGEP(B.getInt8Ty(), createLoad(B, sptr), {createLoad(B, nread, true)}),
sptr
);
#else
B.CreateStore(
createInBoundsGEP(B, createLoad(B, sptr), {createLoad(B, nread, true)}), sptr);
#endif
args->resize(2);
fmt->clear();
}
// recursive helper to capture the arguments
static void parse_type(IRBuilder<> &B, vector<Value *> *args, string *fmt,
Type *type, Value *out,
const map<string, Value *> &locals, bool is_writer) {
if (StructType *st = dyn_cast<StructType>(type)) {
*fmt += "{ ";
unsigned idx = 0;
for (auto field : st->elements()) {
parse_type(B, args, fmt, field, B.CreateStructGEP(type, out, idx++),
locals, is_writer);
*fmt += " ";
}
*fmt += "}";
} else if (ArrayType *at = dyn_cast<ArrayType>(type)) {
if (at->getElementType() == B.getInt8Ty()) {
// treat i8[] as a char string instead of as an array of u8's
if (is_writer) {
*fmt += "\"%s\"";
args->push_back(out);
} else {
// When reading strings, scanf doesn't support empty "", so we need to
// break this up into multiple scanf calls. To understand it, let's take
// an example:
// struct Event {
// u32 a;
// struct {
// char x[64];
// int y;
// } b[2];
// u32 c;
// };
// The writer string would look like:
// "{ 0x%x [ { \"%s\" 0x%x } { \"%s\" 0x%x } ] 0x%x }"
// But the reader string needs to restart at each \"\".
// reader0(const char *s, struct Event *val) {
// int nread, rc;
// nread = 0;
// rc = sscanf(s, "{ %i [ { \"%n", &val->a, &nread);
// if (rc != 1) return -1;
// s += nread; nread = 0;
// rc = sscanf(s, "%[^\"]%n", &val->b[0].x, &nread);
// if (rc < 0) return -1;
// s += nread; nread = 0;
// rc = sscanf(s, "\" %i } { \"%n", &val->b[0].y, &nread);
// if (rc != 1) return -1;
// s += nread; nread = 0;
// rc = sscanf(s, "%[^\"]%n", &val->b[1].x, &nread);
// if (rc < 0) return -1;
// s += nread; nread = 0;
// rc = sscanf(s, "\" %i } ] %i }%n", &val->b[1].y, &val->c, &nread);
// if (rc != 2) return -1;
// s += nread; nread = 0;
// return 0;
// }
*fmt += "\"";
finish_sscanf(B, args, fmt, locals, true);
*fmt = "%[^\"]";
args->push_back(out);
finish_sscanf(B, args, fmt, locals, false);
*fmt = "\"";
}
} else {
*fmt += "[ ";
for (size_t i = 0; i < at->getNumElements(); ++i) {
parse_type(B, args, fmt, at->getElementType(),
B.CreateStructGEP(type, out, i), locals, is_writer);
*fmt += " ";
}
*fmt += "]";
}
} else if (isa<PointerType>(type)) {
*fmt += "0xl";
if (is_writer)
*fmt += "x";
else
*fmt += "i";
} else if (IntegerType *it = dyn_cast<IntegerType>(type)) {
if (is_writer)
*fmt += "0x";
if (it->getBitWidth() <= 8)
*fmt += "%hh";
else if (it->getBitWidth() <= 16)
*fmt += "%h";
else if (it->getBitWidth() <= 32)
*fmt += "%";
else
*fmt += "%l";
if (is_writer)
*fmt += "x";
else
*fmt += "i";
args->push_back(is_writer ? createLoad(B, out) : out);
}
}
// make_reader generates a dynamic function in the instruction set of the host
// (not bpf) that is able to convert c-strings in the pretty-print format of
// make_writer back into binary representations. The encoding of the string
// takes the llvm ir structure format, which closely maps the c structure but
// not exactly (no support for unions for instance).
// The general algorithm is:
// pod types (u8..u64) <= %i
// array types
// u8[] no nested quotes :( <= "..."
// !u8[] <= [ %i %i ... ]
// struct types
// struct { u8 a; u64 b; } <= { %i %i }
// nesting is supported
// struct { struct { u8 a[]; }; } <= { "" }
// struct { struct { u64 a[]; }; } <= { [ %i %i .. ] }
string BPFModule::make_reader(Module *mod, Type *type) {
auto fn_it = readers_.find(type);
if (fn_it != readers_.end())
return fn_it->second;
// int read(const char *in, Type *out) {
// int n = sscanf(in, "{ %i ... }", &out->field1, ...);
// if (n != num_fields) return -1;
// return 0;
// }
IRBuilder<> B(*ctx_);
FunctionType *sscanf_fn_type = FunctionType::get(
#if LLVM_VERSION_MAJOR >= 18
B.getInt32Ty(), {B.getPtrTy(), B.getPtrTy()}, /*isVarArg=*/true);
#else
B.getInt32Ty(), {B.getInt8PtrTy(), B.getInt8PtrTy()}, /*isVarArg=*/true);
#endif
Function *sscanf_fn = mod->getFunction("sscanf");
if (!sscanf_fn) {
sscanf_fn = Function::Create(sscanf_fn_type, GlobalValue::ExternalLinkage,
"sscanf", mod);
sscanf_fn->setCallingConv(CallingConv::C);
sscanf_fn->addFnAttr(Attribute::NoUnwind);
}
string name = "reader" + std::to_string(readers_.size());
#if LLVM_VERSION_MAJOR >= 18
vector<Type *> fn_args({B.getPtrTy(), PointerType::getUnqual(type)});
#else
vector<Type *> fn_args({B.getInt8PtrTy(), PointerType::getUnqual(type)});
#endif
FunctionType *fn_type = FunctionType::get(B.getInt32Ty(), fn_args, /*isVarArg=*/false);
Function *fn =
Function::Create(fn_type, GlobalValue::ExternalLinkage, name, mod);
auto arg_it = fn->arg_begin();
Argument *arg_in = &*arg_it;
++arg_it;
arg_in->setName("in");
Argument *arg_out = &*arg_it;
++arg_it;
arg_out->setName("out");
BasicBlock *label_entry = BasicBlock::Create(*ctx_, "entry", fn);
B.SetInsertPoint(label_entry);
Value *nread = B.CreateAlloca(B.getInt32Ty());
#if LLVM_VERSION_MAJOR >= 18
Value *sptr = B.CreateAlloca(B.getPtrTy());
#else
Value *sptr = B.CreateAlloca(B.getInt8PtrTy());
#endif
map<string, Value *> locals{{"nread", nread}, {"sptr", sptr}};
B.CreateStore(arg_in, sptr);
vector<Value *> args({nullptr, nullptr});
string fmt;
parse_type(B, &args, &fmt, type, arg_out, locals, false);
if (0)
debug_printf(mod, B, "%p %p\n", vector<Value *>({arg_in, arg_out}));
finish_sscanf(B, &args, &fmt, locals, true);
B.CreateRet(B.getInt32(0));
readers_[type] = name;
return name;
}
// make_writer generates a dynamic function in the instruction set of the host
// (not bpf) that is able to pretty-print key/leaf entries as a c-string. The
// encoding of the string takes the llvm ir structure format, which closely maps
// the c structure but not exactly (no support for unions for instance).
// The general algorithm is:
// pod types (u8..u64) => 0x%x
// array types
// u8[] => "..."
// !u8[] => [ 0x%x 0x%x ... ]
// struct types
// struct { u8 a; u64 b; } => { 0x%x 0x%x }
// nesting is supported
// struct { struct { u8 a[]; }; } => { "" }
// struct { struct { u64 a[]; }; } => { [ 0x%x 0x%x .. ] }
string BPFModule::make_writer(Module *mod, Type *type) {
auto fn_it = writers_.find(type);
if (fn_it != writers_.end())
return fn_it->second;
// int write(int len, char *out, Type *in) {
// return snprintf(out, len, "{ %i ... }", out->field1, ...);
// }
IRBuilder<> B(*ctx_);
string name = "writer" + std::to_string(writers_.size());
#if LLVM_VERSION_MAJOR >= 18
vector<Type *> fn_args({B.getPtrTy(), B.getInt64Ty(), PointerType::getUnqual(type)});
#else
vector<Type *> fn_args({B.getInt8PtrTy(), B.getInt64Ty(), PointerType::getUnqual(type)});
#endif
FunctionType *fn_type = FunctionType::get(B.getInt32Ty(), fn_args, /*isVarArg=*/false);
Function *fn =
Function::Create(fn_type, GlobalValue::ExternalLinkage, name, mod);
auto arg_it = fn->arg_begin();
Argument *arg_out = &*arg_it;
++arg_it;
arg_out->setName("out");
Argument *arg_len = &*arg_it;
++arg_it;
arg_len->setName("len");
Argument *arg_in = &*arg_it;
++arg_it;
arg_in->setName("in");
BasicBlock *label_entry = BasicBlock::Create(*ctx_, "entry", fn);
B.SetInsertPoint(label_entry);
map<string, Value *> locals{
{"nread", B.CreateAlloca(B.getInt64Ty())},
};
vector<Value *> args({arg_out, B.CreateZExt(arg_len, B.getInt64Ty()), nullptr});
string fmt;
parse_type(B, &args, &fmt, type, arg_in, locals, true);
GlobalVariable *fmt_gvar = B.CreateGlobalString(fmt, "fmt");
args[2] = createInBoundsGEP(B, fmt_gvar, vector<Value *>({B.getInt64(0), B.getInt64(0)}));
if (0)
debug_printf(mod, B, "%d %p %p\n", vector<Value *>({arg_len, arg_out, arg_in}));
#if LLVM_VERSION_MAJOR >= 18
vector<Type *> snprintf_fn_args({B.getPtrTy(), B.getInt64Ty(), B.getPtrTy()});
#else
vector<Type *> snprintf_fn_args({B.getInt8PtrTy(), B.getInt64Ty(), B.getInt8PtrTy()});
#endif
FunctionType *snprintf_fn_type = FunctionType::get(B.getInt32Ty(), snprintf_fn_args, /*isVarArg=*/true);
Function *snprintf_fn = mod->getFunction("snprintf");
if (!snprintf_fn)
snprintf_fn = Function::Create(snprintf_fn_type, GlobalValue::ExternalLinkage, "snprintf", mod);
snprintf_fn->setCallingConv(CallingConv::C);
snprintf_fn->addFnAttr(Attribute::NoUnwind);
CallInst *call = B.CreateCall(snprintf_fn, args);
call->setTailCall(true);
B.CreateRet(call);
writers_[type] = name;
return name;
}
unique_ptr<ExecutionEngine> BPFModule::finalize_rw(unique_ptr<Module> m) {
Module *mod = &*m;
run_pass_manager(*mod);
string err;
EngineBuilder builder(move(m));
builder.setErrorStr(&err);
#if LLVM_VERSION_MAJOR <= 11
builder.setUseOrcMCJITReplacement(false);
#endif
auto engine = unique_ptr<ExecutionEngine>(builder.create());
if (!engine)
fprintf(stderr, "Could not create ExecutionEngine: %s\n", err.c_str());
return engine;
}
int BPFModule::annotate() {
for (auto fn = mod_->getFunctionList().begin(); fn != mod_->getFunctionList().end(); ++fn)
if (!fn->hasFnAttribute(Attribute::NoInline))
fn->addFnAttr(Attribute::AlwaysInline);
// separate module to hold the reader functions
auto m = ebpf::make_unique<Module>("sscanf", *ctx_);
size_t id = 0;
Path path({id_});
for (auto it = ts_->lower_bound(path), up = ts_->upper_bound(path); it != up; ++it) {
TableDesc &table = it->second;
tables_.push_back(&it->second);
table_names_[table.name] = id++;
GlobalValue *gvar = mod_->getNamedValue(table.name);
if (!gvar) continue;
#if LLVM_VERSION_MAJOR >= 14
{
Type *t = gvar->getValueType();
StructType *st = dyn_cast<StructType>(t);
#else
if (PointerType *pt = dyn_cast<PointerType>(gvar->getType())) {
StructType *st = dyn_cast<StructType>(pt->getElementType());
#endif
if (st) {
if (st->getNumElements() < 2) continue;
Type *key_type = st->elements()[0];
Type *leaf_type = st->elements()[1];
using std::placeholders::_1;
using std::placeholders::_2;
using std::placeholders::_3;
table.key_sscanf = std::bind(&BPFModule::sscanf, this,
make_reader(&*m, key_type), _1, _2);
table.leaf_sscanf = std::bind(&BPFModule::sscanf, this,
make_reader(&*m, leaf_type), _1, _2);
table.key_snprintf = std::bind(&BPFModule::snprintf, this,
make_writer(&*m, key_type), _1, _2, _3);
table.leaf_snprintf =
std::bind(&BPFModule::snprintf, this, make_writer(&*m, leaf_type),
_1, _2, _3);
}
}
}
rw_engine_ = finalize_rw(move(m));
if (!rw_engine_)
return -1;
return 0;
}
StatusTuple BPFModule::sscanf(string fn_name, const char *str, void *val) {
if (!rw_engine_enabled_)
return StatusTuple(-1, "rw_engine not enabled");
auto fn =
(int (*)(const char *, void *))rw_engine_->getFunctionAddress(fn_name);
if (!fn)
return StatusTuple(-1, "sscanf not available");
int rc = fn(str, val);
if (rc < 0)
return StatusTuple(rc, "error in sscanf: %s", std::strerror(errno));
return StatusTuple(rc);
}
StatusTuple BPFModule::snprintf(string fn_name, char *str, size_t sz,
const void *val) {
if (!rw_engine_enabled_)
return StatusTuple(-1, "rw_engine not enabled");
auto fn = (int (*)(char *, size_t,
const void *))rw_engine_->getFunctionAddress(fn_name);
if (!fn)
return StatusTuple(-1, "snprintf not available");
int rc = fn(str, sz, val);
if (rc < 0)
return StatusTuple(rc, "error in snprintf: %s", std::strerror(errno));
if ((size_t)rc == sz)
return StatusTuple(-1, "buffer of size %zd too small", sz);
return StatusTuple::OK();
}
} // namespace ebpf