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[WebAssembly] Generalize section ordering constraints 

Summary:
Changes from using a total ordering of known sections to using a
dependency graph approach. This allows our tools to accept and process
binaries that are compliant with the spec and tool conventions that
would have been previously rejected. It also means our own tools can
do less work to enforce an artificially imposed ordering. Using a
general mechanism means fewer special cases and exceptions in the
ordering logic.

Reviewers: aheejin, dschuff

Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58312

llvm-svn: 354426
This commit is contained in:
Thomas Lively 2019-02-20 02:22:36 +00:00
parent 78750a51d9
commit 9757bba440
3 changed files with 150 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
llvm/include/llvm/Object/Wasm.h
View File

@ -288,40 +288,49 @@ class WasmSectionOrderChecker {
public:
// We define orders for all core wasm sections and known custom sections.
enum : int {
// Sentinel, must be zero
WASM_SEC_ORDER_NONE = 0,
// Core sections
// The order of standard sections is precisely given by the spec.
WASM_SEC_ORDER_TYPE = 1,
WASM_SEC_ORDER_IMPORT = 2,
WASM_SEC_ORDER_FUNCTION = 3,
WASM_SEC_ORDER_TABLE = 4,
WASM_SEC_ORDER_MEMORY = 5,
WASM_SEC_ORDER_GLOBAL = 6,
WASM_SEC_ORDER_EVENT = 7,
WASM_SEC_ORDER_EXPORT = 8,
WASM_SEC_ORDER_START = 9,
WASM_SEC_ORDER_ELEM = 10,
WASM_SEC_ORDER_DATACOUNT = 11,
WASM_SEC_ORDER_CODE = 12,
WASM_SEC_ORDER_DATA = 13,
WASM_SEC_ORDER_TYPE,
WASM_SEC_ORDER_IMPORT,
WASM_SEC_ORDER_FUNCTION,
WASM_SEC_ORDER_TABLE,
WASM_SEC_ORDER_MEMORY,
WASM_SEC_ORDER_GLOBAL,
WASM_SEC_ORDER_EVENT,
WASM_SEC_ORDER_EXPORT,
WASM_SEC_ORDER_START,
WASM_SEC_ORDER_ELEM,
WASM_SEC_ORDER_DATACOUNT,
WASM_SEC_ORDER_CODE,
WASM_SEC_ORDER_DATA,
// Custom sections
// "dylink" should be the very first section in the module
WASM_SEC_ORDER_DYLINK = 0,
WASM_SEC_ORDER_DYLINK,
// "linking" section requires DATA section in order to validate data symbols
WASM_SEC_ORDER_LINKING = 100,
WASM_SEC_ORDER_LINKING,
// Must come after "linking" section in order to validate reloc indexes.
WASM_SEC_ORDER_RELOC = 101,
WASM_SEC_ORDER_RELOC,
// "name" section must appear after DATA. Comes after "linking" to allow
// symbol table to set default function name.
WASM_SEC_ORDER_NAME = 102,
WASM_SEC_ORDER_NAME,
// "producers" section must appear after "name" section.
WASM_SEC_ORDER_PRODUCERS = 103
WASM_SEC_ORDER_PRODUCERS,
// Must be last
WASM_NUM_SEC_ORDERS
};
// Sections that may or may not be present, but cannot be predecessors
static int DisallowedPredecessors[WASM_NUM_SEC_ORDERS][WASM_NUM_SEC_ORDERS];
bool isValidSectionOrder(unsigned ID, StringRef CustomSectionName = "");
private:
int LastOrder = -1; // Lastly seen known section's order
bool Seen[WASM_NUM_SEC_ORDERS] = {}; // Sections that have been seen already
// Returns -1 for unknown sections.
int getSectionOrder(unsigned ID, StringRef CustomSectionName = "");

69
llvm/lib/Object/WasmObjectFile.cpp
View File

@ -1527,7 +1527,7 @@ int WasmSectionOrderChecker::getSectionOrder(unsigned ID,
.StartsWith("reloc.", WASM_SEC_ORDER_RELOC)
.Case("name", WASM_SEC_ORDER_NAME)
.Case("producers", WASM_SEC_ORDER_PRODUCERS)
.Default(-1);
.Default(WASM_SEC_ORDER_NONE);
case wasm::WASM_SEC_TYPE:
return WASM_SEC_ORDER_TYPE;
case wasm::WASM_SEC_IMPORT:
@ -1559,15 +1559,68 @@ int WasmSectionOrderChecker::getSectionOrder(unsigned ID,
}
}
// Represents the edges in a directed graph where any node B reachable from node
// A is not allowed to appear before A in the section ordering, but may appear
// afterward.
int WasmSectionOrderChecker::DisallowedPredecessors[WASM_NUM_SEC_ORDERS][WASM_NUM_SEC_ORDERS] = {
{}, // WASM_SEC_ORDER_NONE
{WASM_SEC_ORDER_TYPE, WASM_SEC_ORDER_IMPORT}, // WASM_SEC_ORDER_TYPE,
{WASM_SEC_ORDER_IMPORT, WASM_SEC_ORDER_FUNCTION}, // WASM_SEC_ORDER_IMPORT,
{WASM_SEC_ORDER_FUNCTION, WASM_SEC_ORDER_TABLE}, // WASM_SEC_ORDER_FUNCTION,
{WASM_SEC_ORDER_TABLE, WASM_SEC_ORDER_MEMORY}, // WASM_SEC_ORDER_TABLE,
{WASM_SEC_ORDER_MEMORY, WASM_SEC_ORDER_GLOBAL}, // WASM_SEC_ORDER_MEMORY,
{WASM_SEC_ORDER_GLOBAL, WASM_SEC_ORDER_EVENT}, // WASM_SEC_ORDER_GLOBAL,
{WASM_SEC_ORDER_EVENT, WASM_SEC_ORDER_EXPORT}, // WASM_SEC_ORDER_EVENT,
{WASM_SEC_ORDER_EXPORT, WASM_SEC_ORDER_START}, // WASM_SEC_ORDER_EXPORT,
{WASM_SEC_ORDER_START, WASM_SEC_ORDER_ELEM}, // WASM_SEC_ORDER_START,
{WASM_SEC_ORDER_ELEM, WASM_SEC_ORDER_DATACOUNT}, // WASM_SEC_ORDER_ELEM,
{WASM_SEC_ORDER_DATACOUNT, WASM_SEC_ORDER_CODE}, // WASM_SEC_ORDER_DATACOUNT,
{WASM_SEC_ORDER_CODE, WASM_SEC_ORDER_DATA}, // WASM_SEC_ORDER_CODE,
{WASM_SEC_ORDER_DATA, WASM_SEC_ORDER_LINKING}, // WASM_SEC_ORDER_DATA,
// Custom Sections
{WASM_SEC_ORDER_DYLINK, WASM_SEC_ORDER_TYPE}, // WASM_SEC_ORDER_DYLINK,
{WASM_SEC_ORDER_LINKING, WASM_SEC_ORDER_RELOC, WASM_SEC_ORDER_NAME}, // WASM_SEC_ORDER_LINKING,
{}, // WASM_SEC_ORDER_RELOC (can be repeated),
{WASM_SEC_ORDER_NAME, WASM_SEC_ORDER_PRODUCERS}, // WASM_SEC_ORDER_NAME,
{WASM_SEC_ORDER_PRODUCERS}, // WASM_SEC_ORDER_PRODUCERS,
};
bool WasmSectionOrderChecker::isValidSectionOrder(unsigned ID,
StringRef CustomSectionName) {
int Order = getSectionOrder(ID, CustomSectionName);
if (Order == -1) // Skip unknown sections
if (Order == WASM_SEC_ORDER_NONE)
return true;
// There can be multiple "reloc." sections. Otherwise there shouldn't be any
// duplicate section orders.
bool IsValid = (LastOrder == Order && Order == WASM_SEC_ORDER_RELOC) ||
LastOrder < Order;
LastOrder = Order;
return IsValid;
// Disallowed predecessors we need to check for
SmallVector<int, WASM_NUM_SEC_ORDERS> WorkList;
// Keep track of completed checks to avoid repeating work
bool Checked[WASM_NUM_SEC_ORDERS] = {};
int Curr = Order;
while (true) {
// Add new disallowed predecessors to work list
for (size_t I = 0;; ++I) {
int Next = DisallowedPredecessors[Curr][I];
if (Next == WASM_SEC_ORDER_NONE)
break;
if (Checked[Next])
continue;
WorkList.push_back(Next);
Checked[Next] = true;
}
if (WorkList.empty())
break;
// Consider next disallowed predecessor
Curr = WorkList.pop_back_val();
if (Seen[Curr])
return false;
}
// Have not seen any disallowed predecessors
Seen[Order] = true;
return true;
}

60
llvm/test/Object/wasm-relocs-and-producers.yaml Normal file
View File

@ -0,0 +1,60 @@
# RUN: yaml2obj %s | llvm-objdump -s - | FileCheck %s
# This is a regression test for an issue with the section order
# checker being overly strict. yaml2obj places the relocations last,
# but the section order checker previously checked that relocations
# came before the producers section, which would cause this test to
# fail.
# CHECK: Contents of section producers:
# CHECK: Contents of section reloc.CODE:
--- !WASM
FileHeader:
Version: 0x00000001
Sections:
- Type: TYPE
Signatures:
- Index: 0
ReturnType: NORESULT
ParamTypes: []
- Type: IMPORT
Imports:
- Module: env
Field: __linear_memory
Kind: MEMORY
Memory:
Initial: 0x00000000
- Module: env
Field: __indirect_function_table
Kind: TABLE
Table:
ElemType: FUNCREF
Limits:
Initial: 0x00000000
- Type: FUNCTION
FunctionTypes: [ 0 ]
- Type: CODE
Relocations:
- Type: R_WASM_FUNCTION_INDEX_LEB
Index: 0
Offset: 0x00000004
Functions:
- Index: 0
Locals: []
Body: 1080808080000B
- Type: CUSTOM
Name: linking
Version: 2
SymbolTable:
- Index: 0
Kind: FUNCTION
Name: foo
Flags: [ VISIBILITY_HIDDEN ]
Function: 0
- Type: CUSTOM
Name: producers
Tools:
- Name: clang
Version: 9.0.0
...