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 Action    name: SetType
This command allows you to specify the type of the current item.

If the cursor is located on a name, the type of the named item will be edited. Otherwise, the current function type (if there is a function) or the current item type (if it has a name) will be edited.

The function type must be entered as a C declaration. Hidden arguments (like 'this' pointer in C++) should be specified explicitly. IDA will use the type information to comment the disassembly with the information about function arguments. It can also be used by the Hex-Rays decompiler plugin for better decompilation.

Here is an example of a function declaration:

        int main(int argc, const char *argv[]);
To delete a type declaration, please enter an empty string.

IDA supports the user-defined calling convention. In this calling convention, the user can explicitly specify the locations of arguments and the return value. For example:

        int __usercall func@<ebx>(int x, int y@<esi>);
denotes a function with 2 arguments: the first argument is passed on the stack (IDA automatically calculates its offset) and the second argument is passed in the ESI register and the return value is stored in the EBX register. Stack locations can be specified explicitly:
        int __usercall runtime_memhash@<^12.4>(void *p@<^0.4>, int q@<^4.4>, int r@<^8.4>)
There is a restriction for a __usercall function type: all stack locations should be specified explicitly or all are automatically calculated by IDA. General rules for the user defined prototypes are:
  - the return value must be in a register.
    Exception: stack locations are accepted for the __golang and __usercall calling conventions.
  - if the return type is 'void', the return location must not be specified
  - if the argument location is not specified, it is assumed to be
    on the stack; consequent stack locations are allocated for such arguments
  - it is allowed to declare nested declarations, for example:
    int **__usercall func16@<eax>(int *(__usercall *x)@<ebx>
                                             (int, long@<ecx>, int)@<esi>);
    Here the pointer "x" is passed in the ESI register;
    The pointed function is a usercall function and expects its second
    argument in the ECX register, its return value is in the EBX register.
    The rule of thumb to apply in such complex cases is to specify the
    the registers just before the opening brace for the parameter list.
  - registers used for the location names must be valid for the current
    processor; some registers are unsupported (if the register name is
    generated on the fly, it is unsupported; inform us about such cases;
    we might improve the processor module if it is easy)
  - register pairs can be specified with a colon like <edx:eax>
  - for really complicated cases this syntax can be used.
IDA also understands the "__userpurge" calling convention. It is the same thing as __usercall, the only difference is that the callee cleans the stack.

The name used in the declaration is ignored by IDA.

If the default calling convention is __golang then explicit specification of stack offsets is permitted. For example:

   int __usercall myfunc<^8>(__int64 arg<^0>);
Function declarations may have the __spoils keyword. It is used to specify the list of registers spoiled by the function. The syntax is the following:
   int __spoils<eax, bh> func(int x);
If the __spoils keyword is present, the specified list overrides the standard spoiled list. For x86, the standard spoiled list is <eax, edx, ecx>. The list of spoiled registers may be empty.

IDA also understands some attributes in declarations. For example:

  int myprnt(int id, const char *format, ...);
This declaration means that myprnt is a print-like function; the format string is the second argument and the variadic argument list starts at the third argument.

Below is the full list of attributes that can be handled by IDA. Please look up the details in the corresponding compiler help pages.

  packed        pack structure/union fields tightly, without gaps
  aligned       specify the alignment
  noreturn      declare as not returning function
  ms_struct     use microsoft layout for the structure/union
  format        possible formats: printf, scanf, strftime, strfmon
For data declarations, the following custom __attribute((annotate(X))) keywords have been added. The control the representation of numbers in the output:
  __bin         unsigned binary number
  __oct         unsigned octal number
  __hex         unsigned hexadecimal number
  __dec         signed decimal number
  __sbin        signed binary number
  __soct        signed octal number
  __shex        signed hexadecimal number
  __udec        unsigned decimal number
  __float       floating point
  __char        character
  __segm        segment name
  __enum()      enumeration member (symbolic constant)
  __off         offset expression (a simpler version of __offset)
  __offset()    offset expression
  __strlit()    string
  __stroff()    structure offset
  __custom()    custom data type and format
  __invsign     inverted sign
  __invbits     inverted bitwise
  __lzero       add leading zeroes
  __tabform()   tabular form
The following additional keywords can be used in type declarations:
  _BOOL1        a boolean type with explicit size specification (1 byte)
  _BOOL2        a boolean type with explicit size specification (2 bytes)
  _BOOL4        a boolean type with explicit size specification (4 bytes)
  __int8        a integer with explicit size specification (1 byte)
  __int16       a integer with explicit size specification (2 bytes)
  __int32       a integer with explicit size specification (4 bytes)
  __int64       a integer with explicit size specification (8 bytes)
  __int128      a integer with explicit size specification (16 bytes)
  _BYTE         an unknown type; the only known info is its size: 1 byte
  _WORD         an unknown type; the only known info is its size: 2 bytes
  _DWORD        an unknown type; the only known info is its size: 4 bytes
  _QWORD        an unknown type; the only known info is its size: 8 bytes
  _OWORD        an unknown type; the only known info is its size: 16 bytes
  _TBYTE        10-byte floating point value
  _UNKNOWN      no info is available
  __pure        pure function: always returns the same value and does not
                modify memory in a visible way
  __noreturn    function does not return
  __usercall    user-defined calling convention; see above
  __userpurge   user-defined calling convention; see above
  __golang      golang calling convention
  __swiftcall   swift calling convention
  __spoils      explicit spoiled-reg specification; see above
  __hidden      hidden function argument; this argument was hidden in the
                source code (e.g. 'this' argument in c++ methods is hidden)
  __return_ptr  pointer to return value; implies hidden
  __struct_ptr  was initially a structure value
  __array_ptr   was initially an array
  __unused      unused function argument
  __cppobj      a c++ style struct; the struct layout depends on this keyword
  __ptr32       explicit pointer size specification (32 bits)
  __ptr64       explicit pointer size specification (64 bits)
  __shifted     shifted pointer declaration
  __high        high level prototype (does not explicitly specify
                hidden arguments like 'this', for example)
                this keyword may not be specified by the user but
                IDA may use it to describe high level prototypes
  __bitmask     a bitmask enum, a collection of bit groups
See also
         Edit|Functions submenu.
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