Here is an explanation of implicit calls to library routines.
This macro, if defined, should expand to a piece of C code that will get expanded when compiling functions for libgcc.a. It can be used to provide alternate names for GCC’s internal library functions if there are ABI-mandated names that the compiler should provide.
This hook should declare additional library routines or rename
existing ones, using the functions
init_one_libfunc defined in optabs.c.
init_optabs calls this macro after initializing all the normal
The default is to do nothing. Most ports don’t need to define this hook.
If false (the default), internal library routines start with two
underscores. If set to true, these routines start with
__muldi3 changes to
currently only affects functions defined in libgcc2.c. If this
is set to true, the tm.h file must also
This macro should return
true if the library routine that
implements the floating point comparison operator comparison in
mode mode will return a boolean, and false if it will
return a tristate.
GCC’s own floating point libraries return tristates from the comparison operators, so the default returns false always. Most ports don’t need to define this macro.
This macro should evaluate to
true if the integer comparison
__cmpdi2) return 0 to indicate that the first
operand is smaller than the second, 1 to indicate that they are equal,
and 2 to indicate that the first operand is greater than the second.
If this macro evaluates to
false the comparison functions return
-1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
in libgcc.a, you do not need to define this macro.
This macro should be defined if the target has no hardware divide instructions. If this macro is defined, GCC will use an algorithm which make use of simple logical and arithmetic operations for 64-bit division. If the macro is not defined, GCC will use an algorithm which make use of a 64-bit by 32-bit divide primitive.
The value of
EDOM on the target machine, as a C integer constant
expression. If you don’t define this macro, GCC does not attempt to
deposit the value of
errno directly. Look in
/usr/include/errno.h to find the value of
EDOM on your
If you do not define
TARGET_EDOM, then compiled code reports
domain errors by calling the library function and letting it report the
error. If mathematical functions on your system use
there is an error, then you should leave
TARGET_EDOM undefined so
matherr is used normally.
Define this macro as a C expression to create an rtl expression that
refers to the global “variable”
errno. (On certain systems,
errno may not actually be a variable.) If you don’t define this
macro, a reasonable default is used.
This hook determines whether a function from a class of functions fn_class is present at the runtime.
Set this macro to 1 to use the "NeXT" Objective-C message sending conventions by default. This calling convention involves passing the object, the selector and the method arguments all at once to the method-lookup library function. This is the usual setting when targeting Darwin/Mac OS X systems, which have the NeXT runtime installed.
If the macro is set to 0, the "GNU" Objective-C message sending convention will be used by default. This convention passes just the object and the selector to the method-lookup function, which returns a pointer to the method.
In either case, it remains possible to select code-generation for the alternate scheme, by means of compiler command line switches.