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Enable variable-width extraction for the TC backend
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Enable variable-width extraction for the TC backend
However note that it still doesn't add varbit support for the deparser
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@mouse-mt @vbnogueira
mouse-mt authored and vbnogueira committed May 29, 2024
1 parent 8ff79b8 commit 5231a9e
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Showing 6 changed files with 329 additions and 32 deletions.
196 changes: 178 additions & 18 deletions backends/ebpf/ebpfParser.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -274,15 +274,25 @@ bool StateTranslationVisitor::preorder(const IR::SelectCase *selectCase) {
return false;
}

void StateTranslationVisitor::compileExtractField(const IR::Expression *expr,
const IR::StructField *field,
unsigned hdrOffsetBits, EBPFType *type) {
unsigned int StateTranslationVisitor::compileExtractField(const IR::Expression *expr,
const IR::StructField *field,
unsigned hdrOffsetBits, EBPFType *type,
const char *sizecode) {
unsigned alignment = hdrOffsetBits % 8;
unsigned widthToExtract = type->as<IHasWidth>().widthInBits();
auto program = state->parser->program;
cstring msgStr;
cstring fieldName = field->name.name;

builder->appendFormat("/* EBPF::StateTranslationVisitor::compileExtractField: field %s",
fieldName);
if (type->is<EBPF::EBPFScalarType>()) {
builder->appendFormat(" (%s scalar)",
type->as<EBPF::EBPFScalarType>().isvariable ? "variable" : "fixed");
}
if (sizecode) builder->appendFormat("\n%s", sizecode);
builder->appendFormat("*/");

msgStr = Util::printf_format("Parser: extracting field %s", fieldName);
builder->target->emitTraceMessage(builder, msgStr.c_str());

Expand Down Expand Up @@ -399,23 +409,135 @@ void StateTranslationVisitor::compileExtractField(const IR::Expression *expr,
msgStr = Util::printf_format("Parser: extracted %s (%u bits)", fieldName, widthToExtract);
builder->target->emitTraceMessage(builder, msgStr.c_str());
}
return (0);
}

void StateTranslationVisitor::compileExtract(const IR::Expression *destination) {
/*
* There has GOT to be a better way to do this, but, given the
* interfaces the rest of the code exports, I don't see anything much
* better. Maybe I've just missed something.
*
* My thinking is that ->toString returns a P4(ish) decompilation of
* the Expression, so we can't use that. The only thing I know of
* that generates C code is to visit() it. But that outputs to a
* SourceCodeBuilder. I tried using a CodeBuilder, but this->builder
* is typed as an EBPF::CodeBuilder, so we can't swap a
* Util::SourceCodeBuilder in instead. So we create a relatively
* transient EBPF::CodeBuilder and output to that (by swapping it into
* this->builder for the duration). This means we need a Target to
* pass when creating the EBPF::CodeBuilder, and Target is a virtual
* base class, demanding implementations for a bunch of methods we
* have no use for. Annoying, but nothing worse; we just provide
* dummies that do nothing.
*
* The returned string is on the heap, allocated with strdup(). It
* would probably be better to make this a std::string or some such,
* but I'm not good enough at C++ to get that right.
*
* Fortunately, this->builder is a pointer, or I'd have to worry about
* copies and moves and try to get _that_ right. But pointers are
* lightweight and totally copyable without issue.
*/
char *StateTranslationVisitor::visit_to_string(const IR::Expression *expr) {
class StringTarget : public Target {
public:
StringTarget(cstring n) : Target(n) {}
#define VB1(a) \
{ (void)a; }
#define VB2(a, b) \
{ \
(void)a; \
(void)b; \
}
#define VB3(a, b, c) \
{ \
(void)a; \
(void)b; \
(void)c; \
}
#define VB4(a, b, c, d) \
{ \
(void)a; \
(void)b; \
(void)c; \
(void)d; \
}
#define VB6(a, b, c, d, e, f) \
{ \
(void)a; \
(void)b; \
(void)c; \
(void)d; \
(void)e; \
(void)f; \
}
#define SB0() \
{ return (""); }
#define SB1(a) \
{ \
(void)a; \
return (""); \
}
virtual void emitLicense(Util::SourceCodeBuilder *b, cstring l) const
VB2(b, l) virtual void emitCodeSection(Util::SourceCodeBuilder *b, cstring n) const
VB2(b, n) virtual void emitIncludes(Util::SourceCodeBuilder *b) const
VB1(b) virtual void emitResizeBuffer(Util::SourceCodeBuilder *b, cstring bf,
cstring o) const
VB3(b, bf, o) virtual void emitTableLookup(Util::SourceCodeBuilder *b, cstring n,
cstring k, cstring v) const
VB4(b, n, k, v) virtual void emitTableUpdate(Util::SourceCodeBuilder *b, cstring n,
cstring k, cstring v) const
VB4(b, n, k, v) virtual void emitUserTableUpdate(Util::SourceCodeBuilder *b, cstring n,
cstring k, cstring v) const
VB4(b, n, k, v) virtual void emitTableDecl(Util::SourceCodeBuilder *b, cstring tn,
TableKind k, cstring kt, cstring vt,
unsigned int sz) const
VB6(b, tn, k, kt, vt, sz) virtual void emitMain(Util::SourceCodeBuilder *b, cstring fn,
cstring an) const
VB3(b, fn, an) virtual cstring dataOffset(cstring b) const SB1(b) virtual cstring
dataEnd(cstring b) const SB1(b) virtual cstring dataLength(cstring b) const
SB1(b) virtual cstring forwardReturnCode() const SB0() virtual cstring
dropReturnCode() const SB0() virtual cstring abortReturnCode() const
SB0() virtual cstring sysMapPath() const SB0() virtual cstring
packetDescriptorType() const SB0()
#undef VB1
#undef VB2
#undef VB3
#undef VB4
#undef VB6
#undef SB0
#undef SB1
};
StringTarget t = StringTarget("stringizer");
auto save = builder;
builder = new EBPF::CodeBuilder(&t);
visit(expr);
auto s = builder->toString();
delete builder;
builder = save;
return (strdup(s.c_str()));
}

void StateTranslationVisitor::compileExtract(const IR::Expression *dest,
const IR::Expression *varsize) {
builder->appendFormat("//compileExtract\n");
builder->appendFormat("// compileExtract: dest = %s\n", dest->toString());
builder->appendFormat("// compileExtract: varsize = %s\n",
varsize ? varsize->toString() : "nil");
cstring msgStr;
auto type = state->parser->typeMap->getType(destination);
auto type = state->parser->typeMap->getType(dest);
auto ht = type->to<IR::Type_StructLike>();
if (ht == nullptr) {
::error(ErrorType::ERR_UNSUPPORTED_ON_TARGET, "Cannot extract to a non-struct type %1%",
destination);
dest);
return;
}

// We expect all headers to start on a byte boundary.
unsigned width = ht->width_bits();
if ((width % 8) != 0) {
::error(ErrorType::ERR_UNSUPPORTED_ON_TARGET,
"Header %1% size %2% is not a multiple of 8 bits.", destination, width);
"Header %1% size %2% is not a multiple of 8 bits.", dest, width);
return;
}

Expand Down Expand Up @@ -465,28 +587,58 @@ void StateTranslationVisitor::compileExtract(const IR::Expression *destination)
builder->newline();
builder->blockEnd(true);

msgStr = Util::printf_format("Parser: extracting header %s", destination->toString());
msgStr = Util::printf_format("Parser: extracting header %s", dest->toString());
builder->target->emitTraceMessage(builder, msgStr.c_str());
builder->newline();

unsigned hdrOffsetBits = 0;
/*
* Some of the tests in this loop appear to be can't-happens. For
* example, when varsize is not nil, there appears to be code
* elsewhere which (a) requires at least one varbit field in the
* header struct and (b) forbids multiple varbit fields in a header,
* so we will have exactly one varbit field. I'm leaving the tests
* in both for the cases which aren't can't-happens and for the sake
* of firewalling in case code elsewhere changes such that the
* can't-happens actually can happen.
*/
bool had_varbit;
had_varbit = false;
for (auto f : ht->fields) {
auto ftype = state->parser->typeMap->getType(f);
char *sizecode = 0;
if (ftype->is<IR::Type_Varbits>()) {
if (varsize == nullptr) {
::error(
ErrorType::ERR_INVALID,
"Extract to a header with a varbit<> member requires two-argument extract()");
return;
} else if (had_varbit) {
::error(ErrorType::ERR_INVALID,
"Two-argument extract() target must not have multiple varbit<> members");
return;
} else {
sizecode = visit_to_string(varsize);
builder->appendFormat("/* compileExtract varbit size = %s */", sizecode);
builder->newline();
had_varbit = true;
}
}
auto etype = EBPFTypeFactory::instance->create(ftype);
auto et = etype->to<IHasWidth>();
if (et == nullptr) {
::error(ErrorType::ERR_UNSUPPORTED_ON_TARGET,
"Only headers with fixed widths supported %1%", f);
"Headers must use defined-widths types: %1%", f);
return;
}
compileExtractField(destination, f, hdrOffsetBits, etype);
hdrOffsetBits += et->widthInBits();
unsigned int advance = compileExtractField(dest, f, hdrOffsetBits, etype, sizecode);
hdrOffsetBits += advance ? advance : et->widthInBits();
}
builder->newline();

if (ht->is<IR::Type_Header>()) {
builder->emitIndent();
visit(destination);
visit(dest);
builder->appendLine(".ebpf_valid = 1;");
}

Expand All @@ -495,7 +647,7 @@ void StateTranslationVisitor::compileExtract(const IR::Expression *destination)
builder->appendFormat("%s += BYTES(%u);", program->headerStartVar.c_str(), width);
builder->newline();

msgStr = Util::printf_format("Parser: extracted %s", destination->toString());
msgStr = Util::printf_format("Parser: extracted %s", dest->toString());
builder->target->emitTraceMessage(builder, msgStr.c_str());

builder->newline();
Expand All @@ -516,12 +668,20 @@ void StateTranslationVisitor::processMethod(const P4::ExternMethod *method) {
auto decl = method->object;
if (decl == state->parser->packet) {
if (method->method->name.name == p4lib.packetIn.extract.name) {
if (expression->arguments->size() != 1) {
::error(ErrorType::ERR_UNSUPPORTED_ON_TARGET,
"Variable-sized header fields not yet supported %1%", expression);
return;
switch (expression->arguments->size()) {
case 1:
compileExtract(expression->arguments->at(0)->expression);
break;
case 2:
compileExtract(expression->arguments->at(0)->expression,
expression->arguments->at(1)->expression);
break;
default:
// Can other size() values occur?
::error(ErrorType::ERR_UNEXPECTED, "extract() with unexpected arg count %1%",
expression->arguments->size());
break;
}
compileExtract(expression->arguments->at(0)->expression);
return;
} else if (method->method->name.name == p4lib.packetIn.length.name) {
builder->append(state->parser->program->lengthVar);
Expand Down
7 changes: 4 additions & 3 deletions backends/ebpf/ebpfParser.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -36,9 +36,9 @@ class StateTranslationVisitor : public CodeGenInspector {
P4::P4CoreLibrary &p4lib;
const EBPFParserState *state;

virtual void compileExtractField(const IR::Expression *expr, const IR::StructField *field,
unsigned hdrOffsetBits, EBPFType *type);
virtual void compileExtract(const IR::Expression *destination);
virtual unsigned int compileExtractField(const IR::Expression *, const IR::StructField *,
unsigned int, EBPFType *, const char *);
virtual void compileExtract(const IR::Expression *dest, const IR::Expression *varsize = 0);
virtual void compileLookahead(const IR::Expression *destination);
void compileAdvance(const P4::ExternMethod *ext);
void compileVerify(const IR::MethodCallExpression *expression);
Expand All @@ -62,6 +62,7 @@ class StateTranslationVisitor : public CodeGenInspector {
return false;
}
bool preorder(const IR::AssignmentStatement *stat) override;
char *visit_to_string(const IR::Expression *);
};

class EBPFParserState : public EBPFObject {
Expand Down
10 changes: 7 additions & 3 deletions backends/ebpf/ebpfType.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -128,16 +128,20 @@ void EBPFScalarType::emit(CodeBuilder *builder) {
}

void EBPFScalarType::declare(CodeBuilder *builder, cstring id, bool asPointer) {
if (EBPFScalarType::generatesScalar(width)) {
if (isvariable) {
builder->appendFormat("struct { u8 data[%d]; u16 curwidth; } %s", (width + 7) >> 3,
id.c_str());
} else if (EBPFScalarType::generatesScalar(width)) {
emit(builder);
if (asPointer) builder->append("*");
builder->spc();
builder->append(id);
} else {
if (asPointer)
if (asPointer) {
builder->appendFormat("u8* %s", id.c_str());
else
} else {
builder->appendFormat("u8 %s[%d]", id.c_str(), bytesRequired());
}
}
}

Expand Down
5 changes: 3 additions & 2 deletions backends/ebpf/ebpfType.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -107,10 +107,11 @@ class EBPFScalarType : public EBPFType, public IHasWidth {
public:
const unsigned width;
const bool isSigned;
const bool isvariable;
explicit EBPFScalarType(const IR::Type_Bits *bits)
: EBPFType(bits), width(bits->size), isSigned(bits->isSigned) {}
: EBPFType(bits), width(bits->size), isSigned(bits->isSigned), isvariable(false) {}
explicit EBPFScalarType(const IR::Type_Varbits *bits)
: EBPFType(bits), width(bits->size), isSigned(false) {}
: EBPFType(bits), width(bits->size), isSigned(false), isvariable(true) {}
unsigned bytesRequired() const { return ROUNDUP(width, 8); }
unsigned alignment() const;
void emit(CodeBuilder *builder) override;
Expand Down
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