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NAME dyncall -- encapsulation of architecture-, OS- and compiler-specific function call semantics SYNOPSIS #include <dyncall.h> DCCallVM * dcNewCallVM(DCsize size); void dcFree(DCCallVM * vm); void dcMode(DCCallVM * vm, DCint mode); void dcReset(DCCallVM * vm); void dcArgBool(DCCallVM * vm, DCbool arg); void dcArgChar(DCCallVM * vm, DCchar arg); void dcArgShort(DCCallVM * vm, DCshort arg); void dcArgInt(DCCallVM * vm, DCint arg); void dcArgLong(DCCallVM * vm, DClong arg); void dcArgLongLong(DCCallVM * vm, DClonglong arg); void dcArgFloat(DCCallVM * vm, DCfloat arg); void dcArgDouble(DCCallVM * vm, DCdouble arg); void dcArgPointer(DCCallVM * vm, DCpointer arg); void dcArgAggr(DCCallVM * vm, const DCaggr * ag, const void * value); DCvoid dcCallVoid(DCCallVM * vm, DCpointer funcptr); DCbool dcCallBool(DCCallVM * vm, DCpointer funcptr); DCchar dcCallChar(DCCallVM * vm, DCpointer funcptr); DCshort dcCallShort(DCCallVM * vm, DCpointer funcptr); DCint dcCallInt(DCCallVM * vm, DCpointer funcptr); DClong dcCallLong(DCCallVM * vm, DCpointer funcptr); DClonglong dcCallLongLong(DCCallVM * vm, DCpointer funcptr); DCfloat dcCallFloat(DCCallVM * vm, DCpointer funcptr); DCdouble dcCallDouble(DCCallVM * vm, DCpointer funcptr); DCpointer dcCallPointer(DCCallVM * vm, DCpointer funcptr); DCpointer dcCallAggr(DCCallVM * vm, DCpointer funcptr, const DCaggr * ag, DCpointer ret); void dcBeginCallAggr(DCCallVM * vm, const DCaggr * ag); void dcArgF(DCCallVM * vm, const DCsigchar * signature, ...); void dcVArgF(DCCallVM * vm, const DCsigchar * signature, va_list args); void dcCallF(DCCallVM * vm, DCValue * result, DCpointer funcptr, const DCsigchar * signature, ...); void dcVCallF(DCCallVM * vm, DCValue * result, DCpointer funcptr, const DCsigchar * signature, va_list args); DCaggr* dcNewAggr(DCsize maxFieldCount, DCsize size); void dcAggrField(DCaggr* ag, DCsigchar type, DCint offset, DCsize array_len, ...); void dcCloseAggr(DCaggr* ag); void dcFreeAggr(DCaggr* ag); DESCRIPTION The dyncall library encapsulates architecture-, OS- and compiler-spe- cific function call semantics in a virtual "bind argument parameters from left to right and then call" interface allowing programmers to call C functions in a completely dynamic manner. In other words, instead of calling a function directly, the dyncall li- brary provides a mechanism to push the function parameters manually and to issue the call afterwards. Since the idea behind this concept is similar to call dispatching mech- anisms of virtual machines, the object that can be dynamically loaded with arguments, and then used to actually invoke the call, is called CallVM. It is possible to change the calling convention used by the CallVM at run-time. Due to the fact that nearly every platform comes with one or more distinct calling conventions, the dyncall library project intends to be a portable and open-source approach to the vari- ety of compiler/toolchain/platform-specific binary interfaces sub- tleties, and so on... dcNewCallVM() creates a new CallVM object, where size specifies the max size of the internal stack that will be allocated and used to bind the arguments to. Use dcFree() to destroy the CallVM object. dcMode() sets the calling convention to use. See dyncall.h for a list of available modes. Note that some mode/platform combinations don't make any sense (e.g. using a PowerPC calling convention on a MIPS plat- form) and are silently ignored. dcReset() resets the internal stack of arguments and prepares it for a new call. This function should be called after setting the initial/main call mode (using dcMode()), but prior to binding arguments to the Cal- lVM (sometimes dcMode() calls are needed after pushing some args, e.g. DC_SIGCHAR_CC_ELLIPSIS_VARARGS, which is used prior to binding varargs of variadic functions). Use it also when reusing a CallVM, as arguments don't get flushed automatically after a function call invocation. Note: you should also call this function after initial creation of the a Cal- lVM object, as dcNewCallVM doesn't do this, implicitly. dcArgBool(), dcArgChar(), dcArgShort(), dcArgInt(), dcArgLong(), dcArgLongLong(), dcArgFloat(), dcArgDouble(), dcArgPointer() and dcArgAggr() are used to bind arguments of the named types to the CallVM object. Arguments should be bound in left to right order regarding the C function prototype. dcCallVoid(), dcCallBool(), dcCallChar(), dcCallShort(), dcCallInt(), dcCallLong(), dcCallLongLong(), dcCallFloat(), dcCallDouble(), dcCallPointer() and dcCallAggr() call the function with the previously bound arguments and return the named type, where funcptr is a pointer to the function to call. After the invocation of the function call, the argument values are still bound to the CallVM and a second call using the same arguments can be issued. Call dcReset() (as described above) to clear the internal argument stack. The interfaces for passing and/or returning aggregates (struct, union) by value need to be explained as they are a bit more complex. Every such argument or return type needs some extra info describing its lay- out via a DCaggr structure (except for non-trivial C++ aggregates, see AGGREGATE DESCRIPTION for more information, below). Passing such argu- ments is then done by using dcArgAggr(), where ag is a pointer to the description and value is a pointer to the aggregate in question. Call- ing a function that returns an aggregate by value is done via two func- tions, dcBeginCallAggr(), which handles special cases to facilitate the implementation and must be called before pushing any arguments, and fi- nally dcCallAggr() where ag is a pointer to the description (for both calls) and ret points to memory large enough to hold the to be returned aggregate. dcCallAggr() returns a pointer to ret. NOTE: C++ non-trivial aggregates (check with the std::is_trivial type trait) need some special handling. First of all, no aggregate descrip- tion is needed and NULL must be passed wherever a DCaggr* argument is needed. Also, as dyncall is oblivious to how to do any custom/non-triv- ial construction or copy, and thus cannot do the copy of the aggregate, passed by-value, itself, the user has to provide such copies, manually, where needed (e.g. when passing such an aggregate as an argument by- value, using dcArgAggr(), in order to preserver the call's by-value se- mantics). dcArgF(), dcVArgF(), dcCallF() and dcVCallF() can be used to bind argu- ments in a printf-style call, using a signature string encoding the ar- gument and return types. The former 2 only bind the arguments to the vm object (and ignore return types specified in the signature), whereas the latter two issue a call to the given function pointer, afterwards. The return value will be stored in result. The signature string also features calling convention mode selection. For information about the signature format, refer to dyncall_signature.h or the dyncall manual. For passing aggregates using dc*F() functions, pass two varargs for each aggregate, first a pointer to DCaggr, then a pointer to the aggre- gate in question. For returning aggregates using those functions, pass two final extra arguments, first a pointer to DCaggr describing the re- turn value, then a pointer to memory large enough to hold it. An ex- plicit call do dcBeginCallAggr() is not needed in those cases, and a pointer to the to be returned aggregate is returned via result. AGGREGATE DESCRIPTION In order to describe an aggregate (except for C++ non-trivial aggre- gates, as mentioned above), create a DCaggr object using dcNewAggr(), where maxFieldCount is greater or equal to the number of fields the ag- gregate has (a nested aggregate or an array is counted as one field), and size is the size of the aggregate (e.g. as determined by sizeof()). dcFreeAggr() destroys the DCaggr object. dcAggrField() is used to describe the aggregate, field-by-field (in or- der), with type being a DC_SIGCHAR_* (see dyncall_signature.h), offset being the offset of the field from the beginning of the aggregate (use C's offsetof(3)), and array_len being the number of array elements, iff the field is an array, otherwise use 1. For nested aggregates (when us- ing DC_SIGCHAR_AGGREGATE as type), one needs to pass the pointer to the nested aggregate's DCaggr object as last argument (in ...). Call dcCloseAggr() after having described all fields of an aggregate. Note that c99 flexible array members do not count as a field, and must be omitted, as passing aggregates with a flexible array member by value in C would also omit it. EXAMPLES Note: none of the examples below perform any error checking for sim- plicity of the example. Let's start with a simple example, making a call to the function sqrt(3). Using the dyncall library, this function would be called as follows: double r; DCCallVM* vm = dcNewCallVM(4096); dcMode(vm, DC_CALL_C_DEFAULT); dcReset(vm); /* call: double sqrt(double x); */ dcArgDouble(vm, 4.2373); r = dcCallDouble(vm, (DCpointer)&sqrt); dcFree(vm); Note that the DCCallVM object can be reused and shouldn't be created and freed per call, for performance reasons. The following examples will omit creation and freeing of the DCCallVM, for simplicity. In a more complicated example, let's call printf(3), which requires a different initial mode, as well as a mode switch for the varargs part: int n_written_chars, r; /* initial callconv mode */ dcMode(vm, DC_CALL_C_ELLIPSIS); dcReset(vm); /* int printf(const char * restrict format, ...); */ dcArgPointer(vm, "my printf(%d) %s string%n"); /* switch mode for varargs part */ dcMode(vm, DC_CALL_C_ELLIPSIS_VARARGS); dcArgInt(vm, 3); dcArgPointer(vm, "format"); dcArgPointer(vm, &n_written_chars); r = dcCallInt(vm, (DCpointer)&printf); C/trivial aggregates by-value Onto an example passing an aggregate by value (note that this is only available on platforms where macro DC__Feature_AggrByVal is defined). E.g. passing the following struct S to f(): struct S { char x[3]; double y; }; void f(int, struct S); requires a DCaggr description of the fields/layout of struct S, and is called as follows: struct S s = { { 56, -23, 0 }, -6.28 }; DCaggr *a = dcNewAggr(2, sizeof(struct S)); dcAggrField(a, DC_SIGCHAR_CHAR, offsetof(struct S, x), 3); dcAggrField(a, DC_SIGCHAR_DOUBLE, offsetof(struct S, y), 1); dcCloseAggr(a); dcMode(vm, DC_CALL_C_DEFAULT); dcArgInt(vm, 999); dcArgAggr(vm, a, &s); dcCallVoid(vm, (DCpointer)&f); dcFreeAggr(a); Let's look at an example returning by value the above struct S from function: struct S g(int, short); Omitting creation of the DCaggr *a description, for simplicity: struct S s; dcMode(vm, DC_CALL_C_DEFAULT); /* needed when returning aggrs by value, *before* pushing args */ dcBeginCallAggr(vm, a); dcArgInt(vm, 9); dcArgShort(vm, 7); dcCallAggr(vm, (DCpointer)&g, a, &s); C++ In our next example, let's look at calling a simple C++ method, with the method declaration being: virtual void Klass::Method(float, int); To keep the example simple, let's assume we have a pointer to this vir- tual method in var mptr (e.g. grabbed from the instance's vtable), and a pointer to the instance in var thisptr: /* thiscall calling convention */ dcMode(vm, DC_CALL_C_DEFAULT_THIS); dcReset(vm); /* C++ methods use this-ptr as first/hidden argument */ dcArgPointer(vm, thisptr); dcArgFloat(vm, 2.3f); dcArgInt(vm, -19); dcCallVoid(vm, (DCpointer)mptr); Extending the last example to a vararg method would need some more dcMode(3) calls. E.g.: virtual void Klass::Method(float, int, ...); would be called as follows: /* thiscall calling convention (to pass this-ptr) */ dcMode(vm, DC_CALL_C_DEFAULT_THIS); dcReset(vm); /* C++ methods use this-ptr as first/hidden argument */ dcArgPointer(vm, thisptr); /* fixed part of arguments */ dcMode(vm, DC_CALL_C_ELLIPSIS); dcArgFloat(vm, 2.3f); dcArgInt(vm, -19); /* variable part of arguments */ dcMode(vm, DC_CALL_C_ELLIPSIS_VARARGS); dcArgInt(vm, 7); dcArgDouble(vm, 7.99); dcCallVoid(vm, (DCpointer)mptr); CONFORMING TO The dyncall library needs at least a c99 compiler with additional sup- port for anonymous structs/unions (which were introduced officially in c11). Given that those are generally supported by pretty much all major c99 conforming compilers (as default extension), it should build fine with a c99 toolchain. Strictly speaking, dyncall conforms to c11, though. SEE ALSO dyncallback(3), dynload(3) and the dyncall manual (available in HTML and PDF format) for more information. AUTHORS Daniel Adler <dadler@uni-goettingen.de> Tassilo Philipp <tphilipp@potion-studios.com> $Mdocdate$ dyncall(3)
NAME | SYNOPSIS | DESCRIPTION | AGGREGATE DESCRIPTION | EXAMPLES | CONFORMING TO | SEE ALSO | AUTHORS
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