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Fossil SCM Build System Documentation (Linux)
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Fossil SCM Build System Documentation (Linux)

Table of Contents

  1. Overview
  2. Makefiles
  3. Build Tools
  4. Source Code Structure
  5. Resource Embedding
  6. Build Process Flow
  7. Component Dependencies

Overview

Fossil is a distributed version control system that builds into a single self-contained executable. The build system uses GNU Make and autoconf/autosetup for configuration. All web UI resources (HTML, CSS, JavaScript, documentation, skins) are embedded directly into the binary as C byte arrays.

The build occurs in several stages:

  1. Configuration (via autosetup, similar to autoconf)
  2. Building code generation tools
  3. Translating source files
  4. Generating headers
  5. Compiling C source
  6. Linking the final binary

Makefiles

1. Makefile.in

Path: /Makefile.in

Purpose: Template Makefile processed by autosetup/configure. Contains placeholders like @CC@, @CFLAGS@, etc. that get substituted during configuration.

Key Variables:

Includes: $(SRCDIR)/main.mk - the actual build rules

2. Makefile

Path: /Makefile

Purpose: Generated from Makefile.in by the configure script. Contains actual values substituted for all placeholders.

Key Features:

Dependency: Regenerates automatically when these change:

3. Makefile.classic

Path: /Makefile.classic

Purpose: Simplified Makefile that doesn't require autosetup/configure. Works out-of-the-box on most Unix systems with minimal dependencies.

Key Differences from Makefile.in:

Platform Detection:

HOST_OS_CMD = uname -s
HOST_OS = $(HOST_OS_CMD:sh)
LIB.SunOS = -lsocket -lnsl -lrt
TCC.DragonFly += -DUSE_PREAD

text

4. src/main.mk

Path: /src/main.mk

Purpose: The core build rules. Auto-generated by tools/makemake.tcl - DO NOT EDIT DIRECTLY.

Contains:

Key Sections:

  1. Source Lists - All .c files in src/
  2. Extra Files - JavaScript, CSS, skins, sounds, images embedded in binary
  3. Translated Sources - src/foo.c → bld/foo_.c (via translate tool)
  4. Object Files - bld/foo_.c → bld/foo.o
  5. Build Tool Rules - How to compile translate, makeheaders, mkindex, etc.
  6. Header Generation - makeheaders dependencies
  7. Final Link - Combining all objects into fossil binary

5. src/Makefile

Path: /src/Makefile

Purpose: Small stub that includes main.mk. Used when building from src/ directory.

Build Tools

The tools/ directory contains C programs and scripts used during the build process. These are compiled first using the build compiler (BCC) before the main fossil source.

Core Build Tools (C Programs)

1. translate.c

Path: tools/translate.c Compiled to: bld/translate

Purpose: Preprocesses Fossil source files to make embedding HTML/SQL easier in C code.

Functionality:

Example:

// Input (src/example.c):
void page_example(void){
  @<html>
  @<h1>Hello World</h1>
  @</html>
}

// Output (bld/example_.c):
void page_example(void){
  cgi_printf("<html>\n");
  cgi_printf("<h1>Hello World</h1>\n");
  cgi_printf("</html>\n");
}

text

Enhancement #1: If preceded by = or ,, generates string literal instead of printf Enhancement #2: Lines ending in \ continue to next line without adding \n Enhancement #3: Comment characters can be set via /* @-comment: -- */

2. makeheaders.c

Path: tools/makeheaders.c Compiled to: bld/makeheaders

Purpose: Automatically generates header files (.h) from source files (.c).

Functionality:

Why Used:

INTERFACE Blocks: Code in #if INTERFACE ... #endif blocks gets extracted to headers

3. mkindex.c

Path: tools/mkindex.c Compiled to: bld/mkindex

Purpose: Scans Fossil source for special comments and generates dispatch tables.

Generates: bld/page_index.h - contains arrays of commands, webpages, and settings

Scans For:

Command Classifications:

Example:

/*
** COMMAND: status
**
** Show the current status of the checkout
*/
void status_cmd(void){
  /* implementation */
}

// mkindex generates entry in dispatch table linking "status" to status_cmd()

text

Output: C arrays mapping names to function pointers with metadata (help text, flags, etc.)

4. mkbuiltin.c

Path: tools/mkbuiltin.c Compiled to: bld/mkbuiltin

Purpose: Embeds external files (JS, CSS, images, docs) as C byte arrays in the binary.

Generates: bld/builtin_data.h - contains all embedded resources

Process:

  1. Reads files listed in EXTRA_FILES
  2. Optionally compresses JavaScript (removes comments, whitespace)
  3. Converts to C byte array: static const unsigned char builtin_file_N[] = {...}
  4. Creates index mapping filenames to arrays

Resources Embedded:

Compression: JavaScript gets minified unless FOSSIL_DEBUG is defined

Command-line:

bld/mkbuiltin --prefix src/ [files...] > bld/builtin_data.h

text

5. mkversion.c

Path: tools/mkversion.c Compiled to: bld/mkversion

Purpose: Generates version information header from Fossil manifest.

Generates: bld/VERSION.h

Inputs:

Outputs in VERSION.h:

Build Hash: Combines manifest UUID with build time for unique identifier per build

6. codecheck1.c

Path: tools/codecheck1.c Compiled to: bld/codecheck1

Purpose: Static analysis tool that validates Fossil source code.

Checks:

Run: During build before linking, validates all translated source files

Utility Tools (Scripts)

7. makemake.tcl

Path: tools/makemake.tcl

Purpose: Generates src/main.mk from source file lists.

Process:

  1. Scans src/ directory for .c files
  2. Scans for embedded resources
  3. Generates build rules for each file
  4. Creates dependency chains
  5. Outputs complete main.mk

Run manually: tclsh tools/makemake.tcl (when adding/removing source files)

8. Other Tools (Not in Main Build)

decode-email.c - Decodes Fossil email notifications sqlcompattest.c - Tests SQLite version compatibility (used by configure) skintxt2config.c - Converts skin .txt files to config format codecheck1.c - Additional code quality checks

Scripts:

Source Code Structure

Directory Layout


src/
├── *.c              - Main source files (150+ files)
├── *.js             - JavaScript for web UI
├── *.css            - Stylesheets
├── *.tcl            - Tcl scripts (diff, merge)
├── config.h         - Configuration macros
├── sounds/          - Alert sound files (.wav)
├── alerts/          - More sound files
└── main.mk          - Build rules (generated)

text

Source File Organization

Fossil uses a modular architecture with ~150+ C source files, each focusing on a specific feature area:

Core Infrastructure

Version Control Core

Web Interface

Features

Utilities

Special Source Files

config.h

Path: src/config.h

Purpose: Central configuration header included by all source files.

Contains:

External Sources (extsrc/)

Path: extsrc/

Contains:

These are external projects included in Fossil's source tree.

Component Interaction Patterns

1. Database Access Pattern

Most components follow this pattern:

#include "config.h"
#include "module.h"

void some_operation(void){
  db_must_be_within_tree();           // Verify in checkout
  db_begin_transaction(DB_WRITE);     // Start transaction

  Blob content = empty_blob;
  blob_read_from_file(&content, "file.txt", RepoFILE);

  db_multi_exec("INSERT INTO ...");   // Database ops

  db_end_transaction(0);              // Commit
  blob_reset(&content);               // Cleanup
}

text

2. Web Page Pattern

/*
** WEBPAGE: /mypage
**
** Description of page for help
*/
void mypage_page(void){
  login_check_credentials();          // Authentication
  style_header("Page Title");         // Header HTML

  @ <h1>Content</h1>                  // HTML via @-lines
  @ <p>More content</p>

  style_footer();                     // Footer HTML
}

text

The @ lines get converted by translate tool into cgi_printf() calls.

3. Command Pattern

/*
** COMMAND: mycommand
**
** Usage: fossil mycommand [OPTIONS]
**
** Help text here
*/
void mycommand_cmd(void){
  db_find_and_open_repository(0, 0);  // Open repo
  verify_all_options();               // Validate flags

  // Command implementation

  db_close(0);                        // Cleanup
}

text

Key Component Dependencies

Content Management:

Checkout Management:

Web UI:

Version Control:

Resource Embedding

Fossil embeds all its web resources, documentation, and assets directly into the executable. This makes it a single self-contained binary with no external dependencies.

What Gets Embedded

1. Skins (skins/)

Path: skins/*/

Each skin directory contains:

Skins Included:

Embedding: mkbuiltin reads these and creates C byte arrays

Access: builtin_file("skins/default/css.txt") returns embedded content

2. JavaScript (src/*.js)

Path: src/*.js

Files Include:

Processing: JavaScript is minified by mkbuiltin (comments and excess whitespace removed)

Embedding: Each file becomes a separate entry in builtin_data.h

Access: Web pages include via builtin_request_js("graph.js")

3. CSS (src/*.css)

Path: src/*.css

Files:

Embedding: Directly embedded as byte arrays

Access: Included in page headers via style.c

4. Sounds (src/sounds/, src/alerts/)

Path: src/sounds/, src/alerts/

Purpose: Alert sounds for notifications

Files:

Format: WAV audio files

Embedding: Binary embedded via mkbuiltin

Access: Browser plays via data URLs

5. WASM and External Resources (extsrc/)

Path: extsrc/

Files:

Purpose: Client-side diagram rendering

Embedding: Binary WASM and JS embedded in builtin_data.h

6. Documentation (www/) - SPECIAL CASE

Path: www/

IMPORTANT: The www/ directory is NOT embedded via mkbuiltin.c!

How www/ Gets Into the Binary:

The www/ directory is handled specially through Fossil's own repository system:

  1. During Build: The www/ files are checked into the Fossil repository used for Fossil's own development

  2. Documentation Access: When Fossil serves documentation:

    • It looks up the file in its own repository
    • Extracts it from the artifact database
    • Serves it as a web page

  3. The doc.c Module:

    • doc.c handles serving embedded documentation
    • Uses doc_page() function to serve /doc/ URLs
    • Extracts files from the repository, not from builtin_data.h

Example: When you access /doc/quickstart.wiki:

  1. doc.c receives the request
  2. Looks up "www/quickstart.wiki" in the repository
  3. Retrieves the artifact from the database
  4. Formats it (wiki → HTML) and serves it

Why This Matters:

Self-Hosting: Fossil's repository database is embedded in the binary during the build (or Fossil uses a bootstrap repository mechanism).

Embedding Mechanism

builtin_data.h Structure

Generated by: bld/mkbuiltin

Contents:

// Array of file data
static const unsigned char builtin_file_0[] = { 0x66, 0x6f, ... };
static const unsigned char builtin_file_1[] = { ... };
...

// Index structure
struct BuiltinFileIndex {
  const char *zName;              // File path
  const unsigned char *pData;     // File data
  int nByte;                      // Size in bytes
};

// Index array
static const struct BuiltinFileIndex builtin_files[] = {
  { "skins/default/css.txt", builtin_file_0, 1234 },
  { "src/graph.js", builtin_file_1, 5678 },
  ...
};

text

Access Functions (builtin.c)

Path: src/builtin.c

Key Functions:

Process:

  1. Web page requests resource
  2. builtin.c searches index by filename
  3. Returns pointer to embedded byte array
  4. Data served directly from memory

Compression: Some resources (JS) are pre-compressed during embedding

Build Integration

Makefile rule:

$(OBJDIR)/builtin_data.h: $(OBJDIR)/mkbuiltin $(EXTRA_FILES)
    $(OBJDIR)/mkbuiltin --prefix $(SRCDIR)/ $(EXTRA_FILES) >$@

text

Dependencies:

Result: Zero external files needed at runtime - entire web UI is self-contained

Build Process Flow

Complete Build Sequence

Stage 1: Configuration

Tool: autosetup (Tcl-based configure system, or manual Makefile.classic)

Input:

Process:

  1. Detect platform (Linux, BSD, etc.)
  2. Find required libraries (zlib, OpenSSL, SQLite)
  3. Check for optional features (Tcl, JSON, FuseFS)
  4. Detect compiler capabilities
  5. Substitute placeholders in Makefile.in

Output:

Key Detections:

Stage 2: Tool Building

Target: $(OBJDIR)/translate, $(OBJDIR)/makeheaders, etc.

Compiler: BCC (build compiler - usually same as TCC but might differ for cross-compilation)

Commands:

cc -o bld/translate tools/translate.c
cc -o bld/makeheaders tools/makeheaders.c
cc -o bld/mkindex tools/mkindex.c
cc -o bld/mkbuiltin tools/mkbuiltin.c
cc -o bld/mkversion tools/mkversion.c
cc -o bld/codecheck1 tools/codecheck1.c

text

Purpose: These tools are needed for subsequent build stages

Note: Built with BCC, not TCC (might be different for cross-compiling)

Stage 3: Version Generation

Target: $(OBJDIR)/VERSION.h

Dependencies: manifest.uuid, manifest, VERSION

Command:

bld/mkversion manifest.uuid manifest VERSION > bld/VERSION.h

text

Output: VERSION.h with build metadata

Contains:

Stage 4: Source Translation

Target: $(OBJDIR)/*_.c (translated sources)

Tool: bld/translate

Process: For each source file:

bld/translate src/add.c > bld/add_.c
bld/translate src/ajax.c > bld/ajax_.c
...

text

Transformation:

Result: bld/ contains translated versions of all src/*.c files

Stage 5: Resource Embedding

Target: $(OBJDIR)/builtin_data.h

Tool: bld/mkbuiltin

Input: All files in EXTRA_FILES (from main.mk):

Command:

bld/mkbuiltin --prefix src/ \
  skins/default/css.txt \
  skins/default/header.txt \
  src/graph.js \
  src/default.css \
  ... \
  > bld/builtin_data.h

text

Output: C header with embedded byte arrays and index

Stage 6: Index Generation

Target: $(OBJDIR)/page_index.h

Tool: bld/mkindex

Input: All translated source files (bld/*_.c)

Command:

bld/mkindex bld/add_.c bld/ajax_.c ... > bld/page_index.h

text

Process:

  1. Scans for WEBPAGE:, COMMAND:, SETTING: comments
  2. Extracts help text
  3. Parses command flags
  4. Generates dispatch tables

Output: C arrays for command/page dispatch

Stage 7: Header Generation

Target: $(OBJDIR)/headers (phony target), $(OBJDIR)/*.h

Tool: bld/makeheaders

Dependencies:

Command:

bld/makeheaders \
  bld/add_.c:bld/add.h \
  bld/ajax_.c:bld/ajax.h \
  ... \
  extsrc/sqlite3.h \
  src/th.h \
  bld/VERSION.h

text

Process:

  1. Parse each .c file
  2. Extract INTERFACE blocks
  3. Extract function signatures
  4. Generate corresponding .h files
  5. Resolve dependencies

Output: Header file for each source file (bld/*.h)

Timestamp: Creates bld/headers timestamp file to track completion

Stage 8: Compilation

Target: $(OBJDIR)/*.o (object files)

Compiler: TCC (target compiler)

Flags:

Process: For each source file:

cc -Wall -O2 -I. -Isrc -Ibld -o bld/add.o -c bld/add_.c
cc -Wall -O2 -I. -Isrc -Ibld -o bld/ajax.o -c bld/ajax_.c
...

text

Dependencies: Each .o depends on:

Special Compilations:

SQLite:

cc $(SQLITE_OPTIONS) -o bld/sqlite3.o -c extsrc/sqlite3.c

text

SQLITE_OPTIONS includes optimizations and feature flags specific to Fossil's usage.

Shell:

cc $(SHELL_OPTIONS) -o bld/shell.o -c extsrc/shell.c

text

Shell is compiled with -Dmain=sqlite3_shell to avoid main() conflict.

Pikchr:

cc $(PIKCHR_OPTIONS) -o bld/pikchr.o -c extsrc/pikchr.c

text

TH (scripting):

cc -o bld/th.o -c extsrc/th.c
cc -o bld/th_lang.o -c extsrc/th_lang.c

text

Stage 9: Code Checking

Target: (implicit in build)

Tool: bld/codecheck1

Input: All translated sources

Command:

bld/codecheck1 bld/*_.c

text

Purpose: Static analysis for Fossil-specific coding standards

Timing: Runs just before linking

Stage 10: Linking

Target: fossil (or APPNAME)

Linker: TCC (target compiler)

Input:

Command:

cc -o fossil \
  bld/add.o bld/ajax.o ... \
  bld/sqlite3.o bld/shell.o bld/pikchr.o ... \

  -lz -lssl -lcrypto -lpthread -lm -ldl

text

Result: Single executable fossil containing everything

Size: Typically 10-15 MB (includes SQLite, all documentation, all web UI)

Build Dependency Graph


configure (auto.def)
    ↓
Makefile, autoconfig.h
    ↓
Build Tools ────────────────┐
(translate, makeheaders,    │
 mkindex, mkbuiltin,        │
 mkversion, codecheck1)     │
    ↓                       │
VERSION.h ←─────────────────┘
    ↓
Translate Sources
(src/*.c → bld/*_.c)
    ↓
builtin_data.h ←── EXTRA_FILES
    ↓
page_index.h ←──── bld/*_.c (scan for WEBPAGE/COMMAND)
    ↓
Headers (bld/*.h) ←── bld/*_.c (via makeheaders)
    ↓
Object Files (bld/*.o) ←── bld/*_.c + bld/*.h
    ↓                      extsrc/*.c
Code Check ←────────── bld/*_.c
    ↓
Link
    ↓
fossil (executable)

text

Incremental Builds

Make's Dependency Tracking:

Clean Targets:

Parallel Builds:

Build Stage Summary Table

Quick reference for the complete build process:

Stage Name Tool/Action Input Output
0 Build Directory mkdir -p bld - bld/
2 Tool Building Compile tools tools/*.c build tools
4 Source Translation bld/translate src/*.c (150) bld/*_.c
6 Index Generation bld/mkindex bld/*_.c page_index.h
5 Resource Embedding bld/mkbuiltin 110+ files builtin_data.h
3 Version Generation bld/mkversion manifest files VERSION.h
7 Header Generation bld/makeheaders bld/*_.c bld/*.h
8 Compilation cc (TCC) bld/*_.c bld/*.o
9 Code Checking bld/codecheck1 bld/*_.c output
10 Linking cc (TCC) All .o files fossil binary

Notes:

Build Verification & Observations

The documented build process has been verified against actual build logs from make clean; make. Key observations:

1. Tool Building Strategy:

2. Dependency Order (Verified): All dependencies are correctly ordered in the build:

3. File Counts (Actual):

4. Parallel Build Capability:

5. Resource Embedding Breakdown: Verified embedded in builtin_data.h (line 158):

6. Compilation Flags Verified:

7. Library Linking (Verified): Final link includes (line 487):

8. Build Reproducibility:

Component Dependencies

Library Dependencies

Required:

Optional:

Platform:

Compilation Order

Must Build First:

  1. All build tools (parallel possible among tools)
  2. VERSION.h
  3. All source translations (parallel possible)
  4. builtin_data.h
  5. page_index.h
  6. All headers (makeheaders processes all files at once)
  7. Object files (parallel possible)
  8. Final link

Cannot Parallelize:

Source File Relationships

Core Dependencies:

Every source file includes:

#include "config.h"     // First - feature flags
#include "module.h"     // Own header (generated by makeheaders)

text

Common Includes:

Web Page Dependencies:

Heavy Interdependencies:

www/ Documentation (Special Case)

Not in builtin_data.h - Documentation lives in the repository itself

Access Pattern:

  1. User requests /doc/file.wiki
  2. doc.c receives request
  3. Looks up www/file.wiki in repository database
  4. Retrieves artifact
  5. Renders (wiki/markdown → HTML)
  6. Serves to user

Repository Embedding:

Summary

The Fossil build system is a sophisticated multi-stage process that has been verified against actual build logs to ensure documentation accuracy.

Build Process Overview

  1. Configures the build for the target platform (autosetup)
  2. Builds tools needed for code generation (translate, makeheaders, etc.)
  3. Transforms source code to embed HTML/SQL (@-lines → C)
  4. Embeds all resources (JS, CSS, skins, sounds) as byte arrays
  5. Generates headers automatically from source
  6. Compiles to object files with proper dependencies
  7. Links into a single self-contained executable

Build Statistics (Verified)

The result is a ~13-15 MB single executable binary containing:

Key Innovations

Files to Read for Deeper Understanding: