From 95fb5f904f7b8c476cdfbd0764864eb3c6ea8de0 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Tue, 12 Mar 2024 10:09:02 +0100
Subject: [PATCH] New linker build option. "system-linker" deprecated and
 removed from project settings.

---
 releasenotes.md                  |   2 +
 src/build/build.h                |  18 ++-
 src/build/build_internal.h       |  11 +-
 src/build/build_options.c        | 208 ++++++++++++++++++-------------
 src/build/builder.c              |  11 +-
 src/build/project.c              |  29 +++--
 src/compiler/compiler.c          |   8 +-
 src/compiler/compiler_internal.h |   1 +
 src/compiler/libraries.c         |  62 ++++-----
 src/compiler/linker.c            |  38 +++---
 10 files changed, 212 insertions(+), 176 deletions(-)

diff --git a/releasenotes.md b/releasenotes.md
index e93cc979a..ac785de61 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -5,6 +5,8 @@
 ### Changes / improvements
 - Disallow multiple `_` in a row in digits, e.g. `1__000`.
 - Added `@link` attribute.
+- New 'linker' build option.
+- "linker" project setting updated, "system-linker" removed.
 
 ### Fixes
 - Struct/union members now correctly rejects members without storage size #1147.
diff --git a/src/build/build.h b/src/build/build.h
index 393e99754..b1904d7a9 100644
--- a/src/build/build.h
+++ b/src/build/build.h
@@ -83,6 +83,14 @@ typedef enum
 	SAFETY_ON = 1,
 } SafetyLevel;
 
+typedef enum
+{
+	LINKER_TYPE_NOT_SET = -1,
+	LINKER_TYPE_BUILTIN = 0,
+	LINKER_TYPE_CC = 1,
+	LINKER_TYPE_CUSTOM = 2,
+} LinkerType;
+
 typedef enum
 {
 	TRUST_NONE,
@@ -330,7 +338,8 @@ typedef struct BuildOptions_
 	const char *target_select;
 	const char *path;
 	const char *template;
-	const char *linker;
+	LinkerType linker_type;
+	const char *custom_linker_path;
 	uint32_t symtab_size;
 	unsigned version;
 	CompilerBackend backend;
@@ -367,7 +376,6 @@ typedef struct BuildOptions_
 	EmitStdlib emit_stdlib;
 	UseStdlib use_stdlib;
 	LinkLibc link_libc;
-	SystemLinker system_linker;
 	StripUnused strip_unused;
 	OptimizationLevel optlevel;
 	SizeOptimizationLevel optsize;
@@ -471,7 +479,7 @@ typedef struct
 	RelocModel reloc_model;
 	ArchOsTarget arch_os_target;
 	CompilerBackend backend;
-	SystemLinker system_linker;
+	LinkerType linker_type;
 	uint32_t symtab_size;
 	uint32_t switchrange_max_size;
 	const char *panicfn;
@@ -483,7 +491,7 @@ typedef struct
 	const char **csource_dirs;
 	const char **csources;
 	const char **feature_list;
-	const char *linker;
+	const char *custom_linker_path;
 	struct
 	{
 		SoftFloat soft_float : 3;
@@ -537,7 +545,7 @@ static BuildTarget default_build_target = {
 		.use_stdlib = USE_STDLIB_NOT_SET,
 		.link_libc = LINK_LIBC_NOT_SET,
 		.emit_stdlib = EMIT_STDLIB_NOT_SET,
-		.system_linker = SYSTEM_LINKER_NOT_SET,
+		.linker_type = LINKER_TYPE_NOT_SET,
 		.single_module = SINGLE_MODULE_NOT_SET,
 		.strip_unused = STRIP_UNUSED_NOT_SET,
 		.symtab_size = DEFAULT_SYMTAB_SIZE,
diff --git a/src/build/build_internal.h b/src/build/build_internal.h
index cf5b5523e..57240dd70 100644
--- a/src/build/build_internal.h
+++ b/src/build/build_internal.h
@@ -25,18 +25,17 @@ static const char *wincrt_linking[3] = {
 	[WIN_CRT_STATIC] = "static",
 };
 
-static const char *trust_level[3] = {
-	[TRUST_NONE] = "none",
-	[TRUST_INCLUDE] = "include",
-	[TRUST_FULL] = "full",
-};
-
 static const char *optsizes[3] = {
 	[SIZE_OPTIMIZATION_NONE] = "none",
 	[SIZE_OPTIMIZATION_SMALL] = "small",
 	[SIZE_OPTIMIZATION_TINY] = "tiny",
 };
 
+static const char *linker[3] = {
+	[LINKER_TYPE_BUILTIN] = "builtin",
+	[LINKER_TYPE_CC] = "cc",
+	[LINKER_TYPE_CUSTOM] = "custom"
+};
 static const char *on_off[2] = {
 	[SAFETY_OFF] = "no",
 	[SAFETY_ON] = "yes",
diff --git a/src/build/build_options.c b/src/build/build_options.c
index 1cf807241..ed6cf2fb5 100644
--- a/src/build/build_options.c
+++ b/src/build/build_options.c
@@ -41,6 +41,12 @@ char *arch_os_target[ARCH_OS_TARGET_LAST + 1] = {
 	[WINDOWS_X64] = "windows-x64",
 };
 
+const char *trust_level[3] = {
+	[TRUST_NONE] = "none",
+	[TRUST_INCLUDE] = "include",
+	[TRUST_FULL] = "full",
+};
+
 #define EOUTPUT(string, ...) fprintf(stderr, string "\n", ##__VA_ARGS__)
 #define OUTPUT(string, ...) fprintf(stdout, string "\n", ##__VA_ARGS__)
 #define FAIL_WITH_ERR(string, ...) do { fprintf(stderr, "Error: " string "\n\n", ##__VA_ARGS__); usage(); exit_compiler(EXIT_FAILURE); } while (0)
@@ -73,104 +79,105 @@ static void usage(void)
 	OUTPUT("  vendor-fetch <library> ...              Fetches one or more libraries from the vendor collection.");
 	OUTPUT("");
 	OUTPUT("Options:");
-	OUTPUT("  --tb                      - Use Tilde Backend for compilation.");
-	OUTPUT("  --stdlib <dir>            - Use this directory as the C3 standard library path.");
-	OUTPUT("  --no-entry                - Do not generate (or require) a main function.");
-	OUTPUT("  --libdir <dir>            - Add this directory to the C3 library search paths.");
-	OUTPUT("  --lib <name>              - Add this library to the compilation.");
-	OUTPUT("  --path <dir>              - Use this as the base directory for the current command.");
-	OUTPUT("  --template <template>     - Select template for 'init': \"exe\", \"static-lib\", \"dynamic-lib\" or a path.");
-	OUTPUT("  --about                   - Prints a short description of C3.");
-	OUTPUT("  --symtab <value>          - Sets the preferred symtab size.");
-	OUTPUT("  -V --version              - Print version information.");
-	OUTPUT("  -E                        - Lex only.");
-	OUTPUT("  -P                        - Only parse and output the AST as JSON.");
-	OUTPUT("  -C                        - Only lex, parse and check.");
-	OUTPUT("  -                         - Read code from standard in.");
-	OUTPUT("  -o <file>                 - Write output to <file>.");
-	OUTPUT("  -O0                       - Safe, no optimizations, emit debug info.");
-	OUTPUT("  -O1                       - Safe, high optimization, emit debug info.");
-	OUTPUT("  -O2                       - Unsafe, high optimization, emit debug info.");
-	OUTPUT("  -O3                       - Unsafe, high optimization, single module, emit debug info.");
-	OUTPUT("  -O4                       - Unsafe, highest optimization, relaxed maths, single module, emit debug info.");
-	OUTPUT("  -O5                       - Unsafe, highest optimization, fast maths, single module, emit debug info.");
-	OUTPUT("  -Os                       - Unsafe, high optimization, small code, single module, no debug info.");
-	OUTPUT("  -Oz                       - Unsafe, high optimization, tiny code, single module, no debug info.");
-	OUTPUT("  -D <name>                 - Add feature flag <name>.");
-	OUTPUT("  -U <name>                 - Remove feature flag <name>.");
-	OUTPUT("  --trust=<option>          - Trust level: none (default), include ($include allowed), full ($exec / exec allowed).");
-	OUTPUT("  --build-dir <dir>         - Override build output directory.");
-	OUTPUT("  --obj-out <dir>           - Override object file output directory.");
-	OUTPUT("  --script-dir <dir>        - Override the base directory for $exec.");
-	OUTPUT("  --llvm-out <dir>          - Override llvm output directory for '--emit-llvm'.");
-	OUTPUT("  --emit-llvm               - Emit LLVM IR as a .ll file per module.");
-	OUTPUT("  --asm-out <dir>           - Override asm output directory for '--emit-asm'.");
-	OUTPUT("  --emit-asm                - Emit asm as a .s file per module.");
-	OUTPUT("  --obj                     - Emit object files. (Enabled by default)");
-	OUTPUT("  --no-obj                  - Do not output object files, this is only valid for `compile-only`.");
-	OUTPUT("  --target <target>         - Compile for a particular architecture + OS target.");
-	OUTPUT("  --threads <number>        - Set the number of threads to use for compilation.");
-	OUTPUT("  --safe=<yes|no>           - Turn safety (contracts, runtime bounds checking, null pointer checks etc) on or off.");
-	OUTPUT("  --optlevel=<option>       - Code optimization level: none, less, more, max.");
-	OUTPUT("  --optsize=<option>        - Code size optimization: none, small, tiny.");
-	OUTPUT("  --single-module=<yes|no>  - Compile all modules together, enables more inlining.");
+	OUTPUT("  --tb                       - Use Tilde Backend for compilation.");
+	OUTPUT("  --stdlib <dir>             - Use this directory as the C3 standard library path.");
+	OUTPUT("  --no-entry                 - Do not generate (or require) a main function.");
+	OUTPUT("  --libdir <dir>             - Add this directory to the C3 library search paths.");
+	OUTPUT("  --lib <name>               - Add this library to the compilation.");
+	OUTPUT("  --path <dir>               - Use this as the base directory for the current command.");
+	OUTPUT("  --template <template>      - Select template for 'init': \"exe\", \"static-lib\", \"dynamic-lib\" or a path.");
+	OUTPUT("  --about                    - Prints a short description of C3.");
+	OUTPUT("  --symtab <value>           - Sets the preferred symtab size.");
+	OUTPUT("  -V --version               - Print version information.");
+	OUTPUT("  -E                         - Lex only.");
+	OUTPUT("  -P                         - Only parse and output the AST as JSON.");
+	OUTPUT("  -C                         - Only lex, parse and check.");
+	OUTPUT("  -                          - Read code from standard in.");
+	OUTPUT("  -o <file>                  - Write output to <file>.");
+	OUTPUT("  -O0                        - Safe, no optimizations, emit debug info.");
+	OUTPUT("  -O1                        - Safe, high optimization, emit debug info.");
+	OUTPUT("  -O2                        - Unsafe, high optimization, emit debug info.");
+	OUTPUT("  -O3                        - Unsafe, high optimization, single module, emit debug info.");
+	OUTPUT("  -O4                        - Unsafe, highest optimization, relaxed maths, single module, emit debug info.");
+	OUTPUT("  -O5                        - Unsafe, highest optimization, fast maths, single module, emit debug info.");
+	OUTPUT("  -Os                        - Unsafe, high optimization, small code, single module, no debug info.");
+	OUTPUT("  -Oz                        - Unsafe, high optimization, tiny code, single module, no debug info.");
+	OUTPUT("  -D <name>                  - Add feature flag <name>.");
+	OUTPUT("  -U <name>                  - Remove feature flag <name>.");
+	OUTPUT("  --trust=<option>           - Trust level: none (default), include ($include allowed), full ($exec / exec allowed).");
+	OUTPUT("  --build-dir <dir>          - Override build output directory.");
+	OUTPUT("  --obj-out <dir>            - Override object file output directory.");
+	OUTPUT("  --script-dir <dir>         - Override the base directory for $exec.");
+	OUTPUT("  --llvm-out <dir>           - Override llvm output directory for '--emit-llvm'.");
+	OUTPUT("  --emit-llvm                - Emit LLVM IR as a .ll file per module.");
+	OUTPUT("  --asm-out <dir>            - Override asm output directory for '--emit-asm'.");
+	OUTPUT("  --emit-asm                 - Emit asm as a .s file per module.");
+	OUTPUT("  --obj                      - Emit object files. (Enabled by default)");
+	OUTPUT("  --no-obj                   - Do not output object files, this is only valid for `compile-only`.");
+	OUTPUT("  --target <target>          - Compile for a particular architecture + OS target.");
+	OUTPUT("  --threads <number>         - Set the number of threads to use for compilation.");
+	OUTPUT("  --safe=<yes|no>            - Turn safety (contracts, runtime bounds checking, null pointer checks etc) on or off.");
+	OUTPUT("  --optlevel=<option>        - Code optimization level: none, less, more, max.");
+	OUTPUT("  --optsize=<option>         - Code size optimization: none, small, tiny.");
+	OUTPUT("  --single-module=<yes|no>   - Compile all modules together, enables more inlining.");
 	OUTPUT("");
-	OUTPUT("  -g                        - Emit debug info.");
-	OUTPUT("  -g0                       - Emit no debug info.");
+	OUTPUT("  -g                         - Emit debug info.");
+	OUTPUT("  -g0                        - Emit no debug info.");
 	OUTPUT("");
 	OUTPUT("");
-	OUTPUT("  -l <library>              - Link with the library provided.");
-	OUTPUT("  -L <library dir>          - Append the directory to the linker search paths.");
-	OUTPUT("  -z <argument>             - Send the <argument> as a parameter to the linker.");
-	OUTPUT("  --system-linker=<yes|no>  - Use the system linker (default: no for cross compilation, yes otherwise).");
-	OUTPUT("  --cc <path>               - Set C compiler (for C files in projects and use as system linker).");
-	OUTPUT("  --linker <path>           - Use the linker in the given path.");
+	OUTPUT("  -l <library>               - Link with the library provided.");
+	OUTPUT("  -L <library dir>           - Append the directory to the linker search paths.");
+	OUTPUT("  -z <argument>              - Send the <argument> as a parameter to the linker.");
+	OUTPUT("  --system-linker=<yes|no>   - Use the system linker (default: no for cross compilation, yes otherwise). [deprecated]");
+	OUTPUT("  --cc <path>                - Set C compiler (for C files in projects and use as system linker).");
+	OUTPUT("  --linker <path>            - Use the linker in the given path. [deprecated]");
+	OUTPUT("  --linker=<option> [<path>] - Linker: builtin, cc, custom (default is 'cc'), 'custom' requires a path.");
 	OUTPUT("");
-	OUTPUT("  --use-stdlib=<yes|no>     - Include the standard library (default: yes).");
-	OUTPUT("  --link-libc=<yes|no>      - Link libc other default libraries (default: yes).");
-	OUTPUT("  --emit-stdlib=<yes|no>    - Output files for the standard library. (default: yes)");
-	OUTPUT("  --panicfn <name>          - Override the panic function name.");
-	OUTPUT("  --testfn <name>           - Override the test runner function name.");
-	OUTPUT("  --benchfn <name>          - Override the benchmark runner function name.");
+	OUTPUT("  --use-stdlib=<yes|no>      - Include the standard library (default: yes).");
+	OUTPUT("  --link-libc=<yes|no>       - Link libc other default libraries (default: yes).");
+	OUTPUT("  --emit-stdlib=<yes|no>     - Output files for the standard library. (default: yes)");
+	OUTPUT("  --panicfn <name>           - Override the panic function name.");
+	OUTPUT("  --testfn <name>            - Override the test runner function name.");
+	OUTPUT("  --benchfn <name>           - Override the benchmark runner function name.");
 	OUTPUT("");
-	OUTPUT("  --reloc=<option>          - Relocation model: none, pic, PIC, pie, PIE.");
-	OUTPUT("  --x86cpu=<option>         - Set general level of x64 cpu: baseline, ssse3, sse4, avx1, avx2-v1, avx2-v2 (Skylake/Zen1+), avx512 (Icelake/Zen4+), native.");
-	OUTPUT("  --x86vec=<option>         - Set max type of vector use: none, mmx, sse, avx, avx512, native.");
-	OUTPUT("  --riscvfloat=<option>     - Set type of RISC-V float support: none, float, double");
-	OUTPUT("  --memory-env=<option>     - Set the memory environment: normal, small, tiny, none.");
-	OUTPUT("  --strip-unused=<yes|no>   - Strip unused code and globals from the output. (default: yes)");
-	OUTPUT("  --fp-math=<option>        - FP math behaviour: strict, relaxed, fast.");
+	OUTPUT("  --reloc=<option>           - Relocation model: none, pic, PIC, pie, PIE.");
+	OUTPUT("  --x86cpu=<option>          - Set general level of x64 cpu: baseline, ssse3, sse4, avx1, avx2-v1, avx2-v2 (Skylake/Zen1+), avx512 (Icelake/Zen4+), native.");
+	OUTPUT("  --x86vec=<option>          - Set max type of vector use: none, mmx, sse, avx, avx512, native.");
+	OUTPUT("  --riscvfloat=<option>      - Set type of RISC-V float support: none, float, double");
+	OUTPUT("  --memory-env=<option>      - Set the memory environment: normal, small, tiny, none.");
+	OUTPUT("  --strip-unused=<yes|no>    - Strip unused code and globals from the output. (default: yes)");
+	OUTPUT("  --fp-math=<option>         - FP math behaviour: strict, relaxed, fast.");
 	OUTPUT("");
-	OUTPUT("  --debug-stats             - Print debug statistics.");
-	OUTPUT("  --print-linking           - Print linker arguments.");
+	OUTPUT("  --debug-stats              - Print debug statistics.");
+	OUTPUT("  --print-linking            - Print linker arguments.");
 #ifndef NDEBUG
-	OUTPUT("  --debug-log               - Print debug logging to stdout.");
+	OUTPUT("  --debug-log                - Print debug logging to stdout.");
 #endif
 	OUTPUT("");
-	OUTPUT("  --benchmarking            - Run built-in benchmarks.");
-	OUTPUT("  --testing                 - Run built-in tests.");
+	OUTPUT("  --benchmarking             - Run built-in benchmarks.");
+	OUTPUT("  --testing                  - Run built-in tests.");
 	OUTPUT("");
-	OUTPUT("  --list-attributes         - List all attributes.");
-	OUTPUT("  --list-builtins           - List all builtins.");
-	OUTPUT("  --list-keywords           - List all keywords.");
-	OUTPUT("  --list-operators          - List all operators.");
-	OUTPUT("  --list-precedence         - List operator precedence order.");
-	OUTPUT("  --list-project-properties - List all available keys used in project.json files.");
-	OUTPUT("  --list-targets            - List all architectures the compiler supports.");
-	OUTPUT("  --list-type-properties    - List all type properties.");
+	OUTPUT("  --list-attributes          - List all attributes.");
+	OUTPUT("  --list-builtins            - List all builtins.");
+	OUTPUT("  --list-keywords            - List all keywords.");
+	OUTPUT("  --list-operators           - List all operators.");
+	OUTPUT("  --list-precedence          - List operator precedence order.");
+	OUTPUT("  --list-project-properties  - List all available keys used in project.json files.");
+	OUTPUT("  --list-targets             - List all architectures the compiler supports.");
+	OUTPUT("  --list-type-properties     - List all type properties.");
 	OUTPUT("");
-	OUTPUT("  --print-output            - Print the object files created to stdout.");
+	OUTPUT("  --print-output             - Print the object files created to stdout.");
 	OUTPUT("");
-	OUTPUT("  --winsdk <dir>            - Set the directory for Windows system library files for cross compilation.");
-	OUTPUT("  --wincrt=<option>         - Windows CRT linking: none, static, dynamic (default).");
-	OUTPUT("  --windef <file>           - Use Windows 'def' file for function exports instead of 'dllexport'.");
+	OUTPUT("  --winsdk <dir>             - Set the directory for Windows system library files for cross compilation.");
+	OUTPUT("  --wincrt=<option>          - Windows CRT linking: none, static, dynamic (default).");
+	OUTPUT("  --windef <file>            - Use Windows 'def' file for function exports instead of 'dllexport'.");
 	OUTPUT("");
-	OUTPUT("  --macossdk <dir>          - Set the directory for the MacOS SDK for cross compilation.");
-	OUTPUT("  --macos-min-version <ver> - Set the minimum MacOS version to compile for.");
-	OUTPUT("  --macos-sdk-version <ver> - Set the MacOS SDK compiled for.");
+	OUTPUT("  --macossdk <dir>           - Set the directory for the MacOS SDK for cross compilation.");
+	OUTPUT("  --macos-min-version <ver>  - Set the minimum MacOS version to compile for.");
+	OUTPUT("  --macos-sdk-version <ver>  - Set the MacOS SDK compiled for.");
 	OUTPUT("");
-	OUTPUT("  --linux-crt <dir>         - Set the directory to use for finding crt1.o and related files.");
-	OUTPUT("  --linux-crtbegin <dir>    - Set the directory to use for finding crtbegin.o and related files.");
+	OUTPUT("  --linux-crt <dir>          - Set the directory to use for finding crt1.o and related files.");
+	OUTPUT("  --linux-crtbegin <dir>     - Set the directory to use for finding crtbegin.o and related files.");
 }
 
 
@@ -674,17 +681,40 @@ static void parse_option(BuildOptions *options)
 				options->single_module = (SingleModule)parse_multi_option(argopt, 2, on_off);
 				return;
 			}
+			if ((argopt = match_argopt("linker")))
+			{
+				options->custom_linker_path = NULL;
+				options->linker_type = (LinkerType) parse_multi_option(argopt, 3, linker);
+				if (options->linker_type == LINKER_TYPE_CUSTOM)
+				{
+					if (at_end() || next_is_opt()) error_exit("error: --linker=custom expects a valid linker name.");
+					options->custom_linker_path = next_arg();
+				}
+				return;
+			}
 			if ((argopt = match_argopt("system-linker")))
 			{
-				options->system_linker = (SystemLinker)parse_multi_option(argopt, 2, on_off);
-				options->linker = NULL;
+				puts("NOTE: 'system-linker' is deprecated, please use --linker instead.");
+				options->custom_linker_path = NULL;
+				switch ((SystemLinker)parse_multi_option(argopt, 2, on_off))
+				{
+					case SYSTEM_LINKER_ON:
+						options->linker_type = LINKER_TYPE_CC;
+						break;
+					case SYSTEM_LINKER_OFF:
+						options->linker_type = LINKER_TYPE_BUILTIN;
+						break;
+					default:
+						UNREACHABLE
+				}
 				return;
 			}
 			if (match_longopt("linker"))
 			{
 				if (at_end() || next_is_opt()) error_exit("error: --linker expects a valid linker name.");
-				options->system_linker = SYSTEM_LINKER_NOT_SET;
-				options->linker = next_arg();
+				options->linker_type = LINKER_TYPE_CUSTOM;
+				options->custom_linker_path = next_arg();
+				puts("NOTE: 'linker' is deprecated, please use --linker=custom <path> instead.");
 				return;
 			}
 			if ((argopt = match_argopt("link-libc")))
@@ -1091,7 +1121,7 @@ BuildOptions parse_arguments(int argc, const char *argv[])
 		.emit_stdlib = EMIT_STDLIB_NOT_SET,
 		.link_libc = LINK_LIBC_NOT_SET,
 		.use_stdlib = USE_STDLIB_NOT_SET,
-		.system_linker = SYSTEM_LINKER_NOT_SET,
+		.linker_type = LINKER_TYPE_NOT_SET,
 		.strip_unused = STRIP_UNUSED_NOT_SET,
 		.single_module = SINGLE_MODULE_NOT_SET,
 		.files = NULL,
diff --git a/src/build/builder.c b/src/build/builder.c
index e2d56e70c..bcec43e57 100644
--- a/src/build/builder.c
+++ b/src/build/builder.c
@@ -277,15 +277,10 @@ static void update_build_target_from_options(BuildTarget *target, BuildOptions *
 	if (options->win.def) target->win.def = options->win.def;
 	if (options->use_stdlib != USE_STDLIB_NOT_SET) target->use_stdlib = options->use_stdlib;
 	if (options->link_libc != LINK_LIBC_NOT_SET) target->link_libc = options->link_libc;
-	if (options->system_linker != SYSTEM_LINKER_NOT_SET)
+	if (options->linker_type != LINKER_TYPE_NOT_SET)
 	{
-		target->system_linker = options->system_linker;
-		target->linker = NULL;
-	}
-	if (options->linker)
-	{
-		target->linker = options->linker;
-		target->system_linker = SYSTEM_LINKER_NOT_SET;
+		target->custom_linker_path = options->custom_linker_path;
+		target->linker_type = options->linker_type;
 	}
 	if (options->emit_stdlib != EMIT_STDLIB_NOT_SET) target->emit_stdlib = options->emit_stdlib;
 	if (options->no_entry) target->no_entry = true;
diff --git a/src/build/project.c b/src/build/project.c
index 3fd311d54..96e176a11 100644
--- a/src/build/project.c
+++ b/src/build/project.c
@@ -21,6 +21,7 @@ const char *project_default_keys[][2] = {
 		{"fp-math", "Set math behaviour: `strict`, `relaxed` or `fast`."},
 		{"langrev", "Version of the C3 language used."},
 		{"linked-libraries", "Libraries linked by the linker for all targets."},
+		{"linker", "'builtin' for the builtin linker, 'cc' for the system linker or <path> to a custom compiler."},
 		{"linker-search-paths", "Linker search paths."},
 		{"link-args", "Linker arguments for all targets."},
 		{"link-libc", "Link libc (default: true)."},
@@ -40,7 +41,6 @@ const char *project_default_keys[][2] = {
 		{"sources", "Paths to project sources for all targets."},
 		{"strip-unused", "Strip unused code and globals from the output. (default: true)"},
 		{"symtab", "Sets the preferred symtab size."},
-		{"system-linker", "Use the system linker (default: no for cross compilation, yes otherwise)."},
 		{"target", "Compile for a particular architecture + OS target."},
 		{"targets", "Set of targets for the project."},
 		{"testfn", "Override the test function."},
@@ -78,6 +78,7 @@ const char* project_target_keys[][2] = {
 		{"langrev", "Version of the C3 language used."},
 		{"linked-libraries-add", "Additional libraries linked by the linker for the target."},
 		{"linked-libraries-override", "Libraries linked by the linker for this target, overriding global settings."},
+		{"linker", "'builtin' for the builtin linker, 'cc' for the system linker or <path> to a custom compiler."},
 		{"linker-search-paths-add", "Additional linker search paths for the target."},
 		{"linker-search-paths-override", "Linker search paths for this target, overriding global settings."},
 		{"link-args-add", "Additional linker arguments for the target."},
@@ -100,7 +101,6 @@ const char* project_target_keys[][2] = {
 		{"sources-override", "Paths to project sources for this target, overriding global settings."},
 		{"strip-unused", "Strip unused code and globals from the output. (default: true)"},
 		{"symtab", "Sets the preferred symtab size."},
-		{"system-linker", "Use the system linker (default: no for cross compilation, yes otherwise)."},
 		{"target", "Compile for a particular architecture + OS target."},
 		{"testfn", "Override the test function."},
 		{"trap-on-wrap", "Make signed and unsigned integer overflow generate a panic rather than wrapping."},
@@ -488,16 +488,27 @@ static void load_into_build_target(JSONObject *json, const char *type, BuildTarg
 	// strip-unused
 	target->strip_unused = (StripUnused)get_valid_bool(json, "strip-unused", type, target->strip_unused);
 
-	// system-linker
-	target->system_linker = (SystemLinker)get_valid_bool(json, "system-linker", type, target->system_linker);
-
 	// linker
-	target->linker = get_string(json, "linker", type, target->linker);
-
-	if (target->system_linker != SYSTEM_LINKER_NOT_SET && target->linker)
+	const char *linker_selection = get_string(json, "linker", type, NULL);
+	if (linker_selection)
 	{
-		error_exit("%s has both 'linker' and 'system-linker' set. They cannot be combined, so please remove one of them.", type);
+		if (str_eq("cc", linker_selection))
+		{
+			target->linker_type = LINKER_TYPE_CC;
+			target->custom_linker_path = NULL;
+		}
+		else if (str_eq("builtin", linker_selection))
+		{
+			target->linker_type = LINKER_TYPE_BUILTIN;
+			target->custom_linker_path = NULL;
+		}
+		else
+		{
+			target->linker_type = LINKER_TYPE_CUSTOM;
+			target->custom_linker_path = linker_selection;
+		}
 	}
+
 	// no-entry
 	target->no_entry = get_valid_bool(json, "no-entry", type, target->no_entry);
 
diff --git a/src/compiler/compiler.c b/src/compiler/compiler.c
index c1d93db09..f9f4bc90a 100644
--- a/src/compiler/compiler.c
+++ b/src/compiler/compiler.c
@@ -493,9 +493,9 @@ void compiler_compile(void)
 		}
 		bool system_linker_available = link_libc() && platform_target.os != OS_TYPE_WIN32;
 		bool use_system_linker = system_linker_available && active_target.arch_os_target == default_target;
-		switch (active_target.system_linker)
+		switch (active_target.linker_type)
 		{
-			case SYSTEM_LINKER_ON:
+			case LINKER_TYPE_CC:
 				if (!system_linker_available)
 				{
 					eprintf("System linker is not supported, defaulting to built-in linker\n");
@@ -503,13 +503,13 @@ void compiler_compile(void)
 				}
 				use_system_linker = true;
 				break;
-			case SYSTEM_LINKER_OFF:
+			case LINKER_TYPE_BUILTIN:
 				use_system_linker = false;
 				break;
 			default:
 				break;
 		}
-		if (use_system_linker || active_target.linker)
+		if (use_system_linker || active_target.linker_type == LINKER_TYPE_BUILTIN)
 		{
 			platform_linker(output_exe, obj_files, output_file_count);
 			compiler_link_time = bench_mark();
diff --git a/src/compiler/compiler_internal.h b/src/compiler/compiler_internal.h
index 8eb4910b5..2015b5da6 100644
--- a/src/compiler/compiler_internal.h
+++ b/src/compiler/compiler_internal.h
@@ -49,6 +49,7 @@ extern const char *project_default_keys[][2];
 extern const int project_default_keys_count;
 extern const char* project_target_keys[][2];
 extern const int project_target_keys_count;
+extern const char *trust_level[3];
 
 typedef struct Ast_ Ast;
 typedef struct Decl_ Decl;
diff --git a/src/compiler/libraries.c b/src/compiler/libraries.c
index 169d60b11..a40ee70d0 100644
--- a/src/compiler/libraries.c
+++ b/src/compiler/libraries.c
@@ -3,6 +3,8 @@
 
 #define MANIFEST_FILE "manifest.json"
 
+static inline void parse_library_target(Library *library, LibraryTarget *target, JSONObject *object);
+
 static inline JSONObject *get_mandatory(Library *library, JSONObject *object, const char *key)
 {
 	JSONObject *value = json_obj_get(object, key);
@@ -43,37 +45,6 @@ static inline const char **get_optional_string_array_as_array(Library *library,
 }
 
 
-static inline void parse_provides(Library *library, JSONObject *object)
-{
-	const char *provides = get_mandatory_string(library, object, "provides");
-	if (!str_is_valid_lowercase_name(provides))
-	{
-		char *res = strdup(provides);
-		str_ellide_in_place(res, 32);
-		error_exit("Invalid 'provides' module name in %s, was '%s'.", library->dir, json_obj_get(object, "provides")->str);
-	}
-	library->provides = provides;
-}
-
-static inline void parse_execs(Library *library, JSONObject *object)
-{
-	library->execs = get_optional_string_array_as_array(library, object, "execs");
-}
-static inline void parse_depends(Library *library, JSONObject *object)
-{
-	library->depends = get_optional_string_array_as_array(library, object, "depends");
-}
-
-static inline void parse_library_run(Library *library, LibraryTarget *target, JSONObject *object)
-{
-	target->execs = get_optional_string_array_as_array(library, object, "execs");
-}
-static inline void parse_library_target(Library *library, LibraryTarget *target, JSONObject *object)
-{
-	target->link_flags = get_optional_string_array_as_array(library, object, "linkflags");
-	target->linked_libs = get_optional_string_array_as_array(library, object, "linked-libs");
-	target->depends = get_optional_string_array_as_array(library, object, "depends");
-}
 static inline void parse_library_type(Library *library, LibraryTarget ***target_group, JSONObject *object)
 {
 	if (!object) return;
@@ -95,16 +66,35 @@ static inline void parse_library_type(Library *library, LibraryTarget ***target_
 	}
 }
 
+static inline void parse_library_target(Library *library, LibraryTarget *target, JSONObject *object)
+{
+	target->link_flags = get_optional_string_array_as_array(library, object, "linkflags");
+	target->linked_libs = get_optional_string_array_as_array(library, object, "linked-libs");
+	target->depends = get_optional_string_array_as_array(library, object, "depends");
+	target->execs = get_optional_string_array_as_array(library, object, "execs");
+}
+
 static Library *add_library(JSONObject *object, const char *dir)
 {
 	Library *library = CALLOCS(Library);
 	library->dir = dir;
-	parse_provides(library, object);
-	parse_depends(library, object);
+	const char *provides = get_mandatory_string(library, object, "provides");
+	if (!str_is_valid_lowercase_name(provides))
+	{
+		char *res = strdup(provides);
+		str_ellide_in_place(res, 32);
+		error_exit("Invalid 'provides' module name in %s, was '%s'.", library->dir,
+		           json_obj_get(object, "provides")->str);
+	}
+	library->provides = provides;
+	library->execs = get_optional_string_array_as_array(library, object, "execs");
+	library->depends = get_optional_string_array_as_array(library, object, "depends");
 	parse_library_type(library, &library->targets, json_obj_get(object, "targets"));
 	return library;
 }
 
+
+
 static Library *find_library(Library **libs, size_t lib_count, const char *name)
 {
 	for (size_t i = 0; i < lib_count; i++)
@@ -260,9 +250,9 @@ void resolve_libraries(void)
 		if (file_is_dir(libdir)) vec_add(active_target.linker_libdirs, libdir);
 		if ((vec_size(library->execs) || vec_size(target->execs)) && active_target.trust_level < TRUST_FULL)
 		{
-			error_exit("Could not use library '%s' as it requires the 'exec' trust level (it "
-			           "is currently %d). Use the '-t' option to enable it.",
-					   library->provides, active_target.trust_level + 1);
+			error_exit("Could not use library '%s' as it requires 'exec' trust level to execute (it "
+			           "is currently '%s'). Use the '--trust=full' option to enable it.",
+					   library->provides, trust_level[active_target.trust_level]);
 		}
 		FOREACH_BEGIN(const char *exec, library->execs)
 			printf("] Execute '%s' for library '%s':", exec, library->provides);
diff --git a/src/compiler/linker.c b/src/compiler/linker.c
index b349bb8ae..476534e18 100644
--- a/src/compiler/linker.c
+++ b/src/compiler/linker.c
@@ -32,7 +32,7 @@ typedef enum
 	LINKER_WASM,
 	LINKER_CC,
 	LINKER_UNKNOWN
-} LinkerType;
+} Linker;
 
 #define add_arg(arg_) vec_add(*args_ref, (arg_))
 #define add_arg2(arg_, arg_2) vec_add(*args_ref, str_cat((arg_), (arg_2)))
@@ -77,7 +77,7 @@ static const char *string_esc(const char *str)
 	return strdup(scratch_buffer_to_string());
 }
 
-static void linker_setup_windows(const char ***args_ref, LinkerType linker_type)
+static void linker_setup_windows(const char ***args_ref, Linker linker_type)
 {
 	add_arg(active_target.win.use_win_subsystem ? "/SUBSYSTEM:WINDOWS" : "/SUBSYSTEM:CONSOLE");
 	global_context_add_link("dbghelp");
@@ -206,7 +206,7 @@ static void linker_setup_windows(const char ***args_ref, LinkerType linker_type)
 	add_arg("/NOLOGO");
 }
 
-static void linker_setup_macos(const char ***args_ref, LinkerType linker_type)
+static void linker_setup_macos(const char ***args_ref, Linker linker_type)
 {
 	if (linker_type == LINKER_CC)
 	{
@@ -311,7 +311,7 @@ static const char *find_linux_crt_begin(void)
 	return NULL;
 }
 
-static void linker_setup_linux(const char ***args_ref, LinkerType linker_type)
+static void linker_setup_linux(const char ***args_ref, Linker linker_type)
 {
 	global_context_add_link("dl");
 	if (linker_type == LINKER_CC)
@@ -377,7 +377,7 @@ static void linker_setup_linux(const char ***args_ref, LinkerType linker_type)
 	add_arg(ld_target(platform_target.arch));
 }
 
-static void linker_setup_freebsd(const char ***args_ref, LinkerType linker_type)
+static void linker_setup_freebsd(const char ***args_ref, Linker linker_type)
 {
 	if (linker_type == LINKER_CC) return;
 	if (is_no_pie(platform_target.reloc_model)) add_arg("-no-pie");
@@ -453,7 +453,7 @@ static void add_linked_libs(const char ***args_ref, const char **libs, bool is_w
 }
 
 static bool linker_setup(const char ***args_ref, const char **files_to_link, unsigned file_count,
-						 const char *output_file, LinkerType linker_type)
+                         const char *output_file, Linker linker_type)
 {
 	bool is_dylib = active_target.type == TARGET_TYPE_DYNAMIC_LIB;
 	bool use_win = linker_type == LINKER_LINK_EXE;
@@ -524,6 +524,10 @@ static bool linker_setup(const char ***args_ref, const char **files_to_link, uns
 		case OS_TYPE_NONE:
 			break;
 	}
+	if (link_libc())
+	{
+		global_context_add_link("m");
+	}
 	for (unsigned i = 0; i < file_count; i++)
 	{
 		add_arg(files_to_link[i]);
@@ -583,7 +587,7 @@ static void append_fpie_pic_options(RelocModel reloc, const char ***args_ref)
 	}
 }
 
-LinkerType linker_find_linker_type(void)
+Linker linker_find_linker_type(void)
 {
 	if (arch_is_wasm(platform_target.arch)) return LINKER_WASM;
 	switch (platform_target.os)
@@ -613,7 +617,7 @@ static bool link_exe(const char *output_file, const char **files_to_link, unsign
 {
 	INFO_LOG("Using linker directly.");
 	const char **args = NULL;
-	LinkerType linker_type = linker_find_linker_type();
+	Linker linker_type = linker_find_linker_type();
 	linker_setup(&args, files_to_link, file_count, output_file, linker_type);
 
 	const char *error = NULL;
@@ -697,11 +701,11 @@ const char *concat_string_parts(const char **args)
 void platform_linker(const char *output_file, const char **files, unsigned file_count)
 {
 	const char **parts = NULL;
-	LinkerType linker_type = LINKER_CC;
-	if (active_target.linker)
+	Linker linker_type = LINKER_CC;
+	if (active_target.linker_type == LINKER_TYPE_CUSTOM)
 	{
-		INFO_LOG("Using linker %s.", active_target.linker);
-		vec_add(parts, active_target.linker);
+		INFO_LOG("Using linker %s.", active_target.custom_linker_path);
+		vec_add(parts, active_target.custom_linker_path);
 		switch (platform_target.object_format)
 		{
 			case OBJ_FORMAT_UNSUPPORTED:
@@ -732,10 +736,6 @@ void platform_linker(const char *output_file, const char **files, unsigned file_
 	}
 
 	linker_setup(&parts, files, file_count, output_file, linker_type);
-	if (link_libc())
-	{
-		vec_add(parts, "-lm");
-	}
 	const char *output = concat_string_parts(parts);
 	if (active_target.print_linking) puts(output);
 	if (system(output) != 0)
@@ -812,14 +812,14 @@ bool dynamic_lib_linker(const char *output_file, const char **files, unsigned fi
 {
 	INFO_LOG("Using linker directly.");
 	const char **args = NULL;
-	if (active_target.linker) vec_add(args, active_target.linker);
-	LinkerType linker_type = linker_find_linker_type();
+	if (active_target.linker_type == LINKER_TYPE_CUSTOM) vec_add(args, active_target.custom_linker_path);
+	Linker linker_type = linker_find_linker_type();
 	linker_setup(&args, files, file_count, output_file, linker_type);
 
 	const char *command = concat_string_parts(args);
 	if (active_target.print_linking) puts(command);
 	DEBUG_LOG("Linker arguments: %s to %d", command, platform_target.object_format);
-	if (active_target.linker)
+	if (active_target.linker_type == LINKER_TYPE_CUSTOM)
 	{
 		if (system(command) != 0)
 		{