[browser][coreCLR] Loading WebCIL 1.0

docs/design/mono/webcil.md

@@ -1,8 +1,8 @@
-# WebCIL assembly format
+# Webcil assembly format
 
 ## Version
 
-This is version 0.0 of the Webcil payload format.
+This is version 1.0 of the Webcil payload format.
 This is version 0 of the WebAssembly module Webcil wrapper.
 
 ## Motivation
@@ -12,7 +12,7 @@ customers that certain users are unable to use their apps because firewalls and
 may prevent browsers from downloading or caching assemblies with a .DLL extension and PE contents.
 
 This document defines a new container format for ECMA-335 assemblies that uses the `.wasm` extension
-and uses a new WebCIL metadata payload format wrapped in a WebAssembly module.
+and uses a new Webcil metadata payload format wrapped in a WebAssembly module.
 
 
 ## Specification
@@ -111,27 +111,27 @@ The Webcil headers consist of a Webcil header followed by a sequence of section
 
 ``` c
 struct WebcilHeader {
-	uint8_t id[4]; // 'W' 'b' 'I' 'L'
-	// 4 bytes
-	uint16_t version_major; // 0
-	uint16_t version_minor; // 0
-	// 8 bytes
-	uint16_t coff_sections;
-	uint16_t reserved0; // 0
-	// 12 bytes
-
-	uint32_t pe_cli_header_rva;
-	uint32_t pe_cli_header_size;
-	// 20 bytes
-
-    uint32_t pe_debug_rva;
-    uint32_t pe_debug_size;
-    // 28 bytes
+  uint8_t id[4]; // 'W' 'b' 'I' 'L'
+  // 4 bytes
+  uint16_t version_major; // 1
+  uint16_t version_minor; // 0
+  // 8 bytes
+  uint16_t coff_sections;
+  uint16_t reserved0; // 0
+  // 12 bytes
+
+  uint32_t pe_cli_header_rva;
+  uint32_t pe_cli_header_size;
+  // 20 bytes
+
+  uint32_t pe_debug_rva;
+  uint32_t pe_debug_size;
+  // 28 bytes
 };
 ```
 
 The Webcil header starts with the magic characters 'W' 'b' 'I' 'L' followed by the version in major
-minor format (must be 0 and 0).  Then a count of the section headers and two reserved bytes.
+minor format (must be 1 and 0).  Then a count of the section headers and two reserved bytes.
 
 The next pairs of integers are a subset of the PE Header data directory specifying the RVA and size
 of the CLI header, as well as the directory entry for the PE debug directory.
@@ -140,25 +140,47 @@ of the CLI header, as well as the directory entry for the PE debug directory.
 #### Section header table
 
 Immediately following the Webcil header is a sequence (whose length is given by `coff_sections`
-above) of section headers giving their virtual address and virtual size, as well as the offset in
-the Webcil payload and the size in the file.  This is a subset of the PE section header that includes
-enough information to correctly interpret the RVAs from the webcil header and from the .NET
-metadata. Other information (such as the section names) are not included.
+above) of PE/COFF `IMAGE_SECTION_HEADER` structures (40 bytes each).  Each header contains the
+section name, virtual address and size, file offset and size, and other PE section attributes.
+Unused fields (such as `PointerToRelocations`, `NumberOfRelocations`, `PointerToLinenumbers`,
+`NumberOfLinenumbers`, and `Characteristics`) are set to zero.  The `Name` field is copied from
+the original PE section header.
+
+Using the standard `IMAGE_SECTION_HEADER` layout allows runtimes to reference the section headers
+directly from the loaded file image without converting from a compact representation at load time.
 
 ``` c
+// IMAGE_SECTION_HEADER — 40 bytes, same layout as PE/COFF
 struct SectionHeader {
-    uint32_t st_virtual_size;
-    uint32_t st_virtual_address;
-    uint32_t st_raw_data_size;
-    uint32_t st_raw_data_ptr;
+    char     Name[8];
+    uint32_t VirtualSize;
+    uint32_t VirtualAddress;
+    uint32_t SizeOfRawData;
+    uint32_t PointerToRawData;
+    uint32_t PointerToRelocations; // 0
+    uint32_t PointerToLinenumbers; // 0
+    uint16_t NumberOfRelocations;  // 0
+    uint16_t NumberOfLinenumbers;  // 0
+    uint32_t Characteristics;      // 0
 };
 ```
 
-(**Note**: the `st_raw_data_ptr` member is an offset from the beginning of the Webcil payload, not from the beginning of the WebAssembly wrapper module.)
+(**Note**: the `PointerToRawData` member is an offset from the beginning of the Webcil payload, not from the beginning of the WebAssembly wrapper module.)
 
 #### Sections
 
-Immediately following the section table are the sections.  These are copied verbatim from the PE file.
+The section data starts at the first 16-byte-aligned offset after the end of the
+section header table. Any gap between the last section header and the first section's
+raw data is filled with zero-valued padding bytes. Each subsequent section likewise
+begins at a 16-byte-aligned offset. This alignment guarantees that RVA static fields
+(such as those backing `ReadOnlySpan<T>` over types up to `Vector128<T>`) retain
+their natural alignment when the payload is loaded into memory at a 16-byte-aligned
+base address.
+
+Because PE `SizeOfRawData` is normally a multiple of the PE `FileAlignment` (≥ 512),
+the inter-section padding is almost always zero bytes. In the worst case a single
+assembly may gain up to ~30 bytes of padding total (header-to-first-section plus
+one boundary per additional section).
 
 ### Rationale
 

eng/testing/tests.browser.targets

@@ -59,10 +59,9 @@
     <WasmTestLogExitCode>true</WasmTestLogExitCode>
   </PropertyGroup>
 
-  <!-- TODO-WASM https://github.com/dotnet/runtime/issues/120248 (CoreCLR on wasm defaults) -->
+  <!-- TODO-WASM github.com/dotnet/runtime/issues/120226 (CoreCLR on wasm defaults) -->
   <PropertyGroup Condition="'$(RuntimeFlavor)' == 'CoreCLR'">
     <InvariantGlobalization Condition="'$(InvariantGlobalization)' == ''">false</InvariantGlobalization>
-    <WasmEnableWebcil>false</WasmEnableWebcil>
   </PropertyGroup>
 
   <ItemGroup>

src/coreclr/inc/pedecoder.h

@@ -46,6 +46,10 @@ typedef DPTR(struct READYTORUN_SECTION) PTR_READYTORUN_SECTION;
 
 typedef DPTR(IMAGE_COR20_HEADER)    PTR_IMAGE_COR20_HEADER;
 
+#ifdef TARGET_BROWSER
+#include "webcil.h"
+#endif // TARGET_BROWSER
+
 // --------------------------------------------------------------------------------
 // Forward declared types
 // --------------------------------------------------------------------------------
@@ -167,6 +171,17 @@ class PEDecoder
     BOOL HasNTHeaders() const;
     CHECK CheckNTHeaders() const;
 
+#ifdef TARGET_BROWSER
+    BOOL HasWebcilHeaders() const;
+    CHECK CheckWebcilHeaders() const;
+    inline BOOL HasHeaders() const { return HasWebcilHeaders() || HasNTHeaders(); }
+#else
+    inline BOOL HasWebcilHeaders() const { return FALSE; }
+    inline BOOL HasHeaders() const { return HasNTHeaders(); }
+#endif
+
+    CHECK CheckHeaders() const;
+
     IMAGE_NT_HEADERS32 *GetNTHeaders32() const;
     IMAGE_NT_HEADERS64 *GetNTHeaders64() const;
     BOOL Has32BitNTHeaders() const;
@@ -189,7 +204,6 @@ class PEDecoder
     SIZE_T GetSizeOfHeapCommit() const;
     UINT32 GetLoaderFlags() const;
     UINT32 GetWin32VersionValue() const;
-    COUNT_T GetNumberOfRvaAndSizes() const;
     COUNT_T GetNumberOfSections() const;
     PTR_IMAGE_SECTION_HEADER FindFirstSection() const;
     IMAGE_SECTION_HEADER *FindSection(LPCSTR sectionName) const;
@@ -365,6 +379,8 @@ class PEDecoder
 
     IMAGE_DATA_DIRECTORY *GetMetaDataHelper(METADATA_SECTION_TYPE type) const;
 
+    COUNT_T GetNumberOfRvaAndSizes() const;
+
     static PTR_IMAGE_SECTION_HEADER FindFirstSection(IMAGE_NT_HEADERS * pNTHeaders);
 
     IMAGE_COR20_HEADER *FindCorHeader() const;
@@ -399,6 +415,8 @@ class PEDecoder
         FLAG_NATIVE_CHECKED     = 0x80,
 
         FLAG_HAS_NO_READYTORUN_HEADER = 0x100,
+        FLAG_WEBCIL             = 0x200,
+        FLAG_WEBCIL_CHECKED     = 0x400,
     };
 
     TADDR               m_base;