custom_calling_convention

summary: implement a custom calling convention

description:

The Delphi LStrCatN variadic function is unusual in the sense that it is variadic, purges the bytes from the stack, and the number of bytes to purge is held in EDX. This example shows how to add support for such ad-hoc calling conventions.

You can test this example with the IDB at ../idbs/delphi6_lstrcatn.i64

keywords: types

level: intermediate

Attributes

EAX

EDX

REGARGS

ccid

Classes

delphi_LStrCatN_cc

Module Contents

custom_calling_convention.EAX = 0
custom_calling_convention.EDX = 2
custom_calling_convention.REGARGS
class custom_calling_convention.delphi_LStrCatN_cc

Bases: ida_typeinf.custom_callcnv_t

name = '__lstrcatn'

the name is used as a keyword in the function prototype

flags
abibits

abibits to be used for the calling convention

validate_func(fti)

Validate a function prototype. This function is used during parsing or deserializing a function prototype to verify semantic limitations of the prototype (for example, returning arrays is forbidden in C)

Parameters:

  • fti – function prototype

  • reterr – buffer for error message

calc_retloc(fti)

Calculate the location of the return value. This function must fill fti->retloc.

Parameters:

fti – function prototype

Returns:

success

calc_arglocs(fti)

Calculate the argument locations. This function must fill all fti->at(i).argloc instances. It may be called for variadic functions too, in calc_varglocs fails.

Parameters:

fti – function prototype

Returns:

success

find_edx_value(call_ea, blk)
find_varargs(fti, call_ea, blk)

Discover variadic arguments. This function is called only for variadic functions. It is currently used by the decompiler.

Parameters:

  • fti – function prototype. find_varargs() should append the discovered variadic arguments to it.

  • call_ea – address of the call instruction

  • blk – microcode block with the call instruction

Returns:

>0 - total number of arguments after the call <0 - failure ==0 - means to use the standard algorithm to discover variadic args

calc_varglocs(fti, regs, stkargs, nfixed)

Calculate the argument locations for a variadic function. This function must fill all fti->at(i).argloc instances and provide more detailed info about registers and stkargs.

Parameters:

  • fti – function prototype

  • regs – buffer for hidden register arguments, may be nullptr

  • stkargs – buffer for hidden stack arguments, may be nullptr

  • nfixed – number of fixed arguments

Returns:

success

get_cc_regs(callregs)

Retrieve generic information about call registers.

get_stkarg_area_info(stkarg_area_info)

Retrieve generic information about stack arguments.

calc_purged_bytes(fti, call_ea)

Calculate the number of purged bytes

Parameters:

  • fti – function prototype

  • call_ea – address of the call instruction (not used yet)

decorate_name(name, should_decorate, cc, ftype)

Function to be overloaded for custom calling conventions.

Decorate a function name. Some compilers decorate names depending on the calling convention. This function provides the means to handle it for custom callcnvs. Please note that this is about name decoration (C), not name mangling (C++).

custom_calling_convention.ccid