Using GDC

Usage of GDC

Simple Compilation

Creating an executable is quite easy.

gdc main.d -o main

This will attempt to compile and link the file 'main.d' and place the output into the file 'main'. If you do not use the -o switch, then your executable will be called 'a.out'.

On a typical Unix system, you can execute the resulting program with "./main" or "./a.out". On Windows, you can run the program with "main" or "a.out".(?)

To help make a transition from DMD to GDC easier, there is a script called 'gdmd' which maps DMD's command line options to GDC. To see the available options for gdmd, type 'gdmd' or 'gdmd -help' on the command line.

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Command line switches

Many of the options in GCC may also be applicable to GDC, such as optimization flags, -O1, -O2, -Os, -O3, or flags such as -c, which compiles a file, but does not link it, and will send the object file to "main.o", if you file is main.d

Compiler Options

Switch	Description
-debuglib=<lib>	Link against a debug <lib> instead of Phobos.
-defaultlib=<lib>	Link against <lib> instead of Phobos.
-fdeps	Print information about module dependencies.
-fdeps=<file>	Write module dependencies to <file>.
-fdoc	Generate Ddoc documentation.
-fdoc-dir=<dir>	Write Ddoc documentation files to <dir>.
-fdoc-file=<file>	Write Ddoc documentation to <file>.
-fdoc-inc=<file>	Include a Ddoc macro <file>.
-fintfc	Generate D interface files,
-fintfc-dir=<dir>	Write D interface files to directory <dir>.
-fintfc-file=<file>	Write D interface file to <file>.
-fmake-deps	Print information about module Makefile dependencies.
-fmake-deps=<file>	Write Makefile dependency output to <file>.
-fmake-mdeps	Like -fmake-deps but ignore system modules.
-fmake-mdeps=<file>	Like -fmake-deps=<file> but ignore system modules.
-fonly=<file>	Process all modules specified on the command line, but only generate code for the module <file>.
-fXf=<file>	Write JSON documenation to <file>.
-imultilib <dir>	Set <dir> to be the multilib include subdirectory.
-iprefix <path>	Specify <path> as a prefix for next two options.
-isysroot <dir>	Set <dir> to be the system root directory.
-isystem <dir>	Add <dir> to the start of the system include path.
-I <dir>	Add <dir> to the list of the module import paths.
-J <dir>	Add <dir> to the list of string import paths.
-nophoboslib	Do not link the standard D library in the compilation. The D standard library, Phobos, and the D runtime are compiled into a single library, libgphobos2. Therefore, this option prevents linking both Phobos and the D runtime.
-nostdinc	Do not search standard system include directories.
-nostdlib	Do not link the standard gcc libraries in the compilation.

Language Options

Most of these have both positive and negative forms; the negative form of -ffoo is -fno-foo. This page lists only one of these two forms, whichever one is not the default.

Switch	Description
-fno-assert	Don't generate runtime code for the assert keyword.
-fno-bounds-check	Don't generate runtime code for checking array bounds before indexing.
-fno-builtin	Don't recognize built-in functions.
-fno-debug	Don't compile debug code.
-fdebug=<level>	Compile in debug code less than or equal to that in <level>.
-fdebug=<ident>	Compile in debug code identified by <ident>.
-fd-verbose	Print information about D language processing to stdout.
-fd-vtls	Print information about all variables going into thread local storage to stdout.
-femit-templates	Generate code for all template instantiations, not just used instantiations.
-fno-in	Don't compile in contracts.
-fno-invariants	Don't compile invariant contracts.
-fno-emit-moduleinfo	Don't generate any ModuleInfo.
-fno-out	Don't compile out contracts.
-fproperty	Enforce @property syntax of D code.
-frelease	Compile release version. Equivalent to -fno-invariants -fno-in -fno-out -fno-assert -fno-bounds-check.
-funittest	Compile unittest code.
-fversion=<level>	Compile in version code greater than or equal to that in <level>.
-fversion=<ident>	Compile in version code identified by <ident>.
-Wall	Enable most warning messages.
-Werror	Error out the compiler on warnings.
-Wdeprecated	Enable warning of deprecated language features.
-Wunknown-pragmas	Enable warning of unsupported pragmas.

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Extensions

Extended Assembler

GDC implements a GCC extension that allows inline assembler with D expression operands. It is available on nearly all targets, not just i386. The syntax differs from the C language extension in the following ways:

• Statements start with 'asm { ...', just like the regular DMD inline assembler.
• It is not necesary to put parentheses around operands.
• Instruction templates can be compile-time string constants, not just string literals. If the template is not a string literal, use parenthesis to indicate that it is not an opcode.

Unlike i386 inline assembler statements, extended assembler statements do not prevent a function from being inlined.

See the GCC manual for more information about this extension.

Example:

uint invert(uint v)
{
    uint result;
    version(X86)
       asm{ "notl %[iov]" : [iov] "=r" result : "0" v; }
    else version(PPC)
       asm{ "nor %[oresult],%[iv],%[iv]" : [oresult] "=r" result : [iv] "r" v; }
    return result;
}

Attributes

GDC supports a small subset of the GCC attributes. The syntax differs from the C language __attribute__ extension in the following ways:

• All attributes are recognised only through the 'gcc.attribute' module.
• The attribute, and all its arguments are comma-dellimied CTFE strings packed in a tuple.
• Nesting (brackets) for attribute arguments are optional.

Attribute	Description
forceinline*	Inlines the function even if no optimization level is specified.
flatten*	Inlines every call inside this function, if possible.
noinline*	Prevents the function from being considered for inlining.
target*	Specify that the function is to be compiled with different target options than specified on the command line.
noclone*	See GCC documentation.
section*	Place symbol in specific section. See GCC documentation.
weak*	Mark symbol as weak. See GCC documentation.
alias*	Mark symbol as an alias (on object file level). See GCC documentation.
architecture specific attributes	All target specific attributes are available. See GCC documentation.

* Being backend attributes, you can't enforce that these attributes actually take effect in user code (no static asserts!) - but you have some guarantee in that the backend will complain if it can't apply the attribute

Example:

import gcc.attribute;

@attribute("noinline") void foobar() { }

@attribute("target", ("sse3")) void sse3_func() { }

//Can be overwritten in other source files
@attribute("weak") extern(C) void c_func() {};
@attribute("alias", "c_func") void aliased_func();

//Place into "test" section
@attribute("section", "test") int value;

Known Issues

See bugzilla to see bugs that have been reported to GDC.

More bugs may be found here.

Some more known issues, taken from here:

• See DStress for known failing cases. (Again, may be irrelevant)
• Debugging information may have a few problems. For D symbol name demangling you need at least gdb 7.2.
• Some targets do not support once-only linking. A workaround is to manually control template emission. See the -femit-templates option below. For Darwin, Apple's GCC 3.x compiler supports one-only linking, but GDC does not build with those sources. There are no problems with the stock GCC 4.x on Darwin.
• Complex floating point operations may not work the same as DMD.
• Some math functions behave differently due to different implementations of the extended floating-point type.
• Volatile statements may not always do the right thing.
• Because of a problem on AIX, the linker will pull in more modules than needed.
• Some C libraries (Cygwin, MinGW, AIX) don't handle floating-point formatting and parsing in a standard way.

See also

• GDC