Re: [fpc-pascal] Calling function pointer to main program
> On Jan 3, 2020, at 12:29 PM, Jonas Maebe wrote: > > So add 'cdecl; public;" to its declaration and definition. Nice the demo program compiles now. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Calling function pointer to main program
On 03/01/2020 20:19, Ryan Joseph via fpc-pascal wrote: >> On Jan 3, 2020, at 11:35 AM, Jonas Maebe wrote: >> >> Additionally, you will also have to link in an object/library that does >> define a regular "main" function. And note that this will only work on >> libc-based targets (afaik only Darwin, Solaris, and AIX at this point). > So there needs to be a function named "main" that is linked to directly or > can it just be in a unit? I tried doing this but still get linker errors > (tested on MacOS of course). My example program is below. > > It's possible I think -XM does something it doesn't also so here's is the > main function for the SDL/ios bindings. Note how UIApplicationMain is called > which then never returns control until the program exists. After that within > the iOS event handlers a call is made to SDL_main (see the external > definition) which if I understand correctly is set using -XP and this then in > turn calls the begin..end block of the main Pascal program. Is that correct? The OS startup code always calls a C function called "main" with the default C main function arguments. By default, FPC names the main entry point symbol of the program "main". -XM simply changes this name. Your errors are that your main function in your unit 1) is not declared as "cdecl", so it uses the wrong calling convention 2) additionally, is not declared as "public", so the only the default (Pascal-mangled) symbol is created for it (in combination with cdecl, this will add a C-mangled alias to it). So add 'cdecl; public;" to its declaration and definition. Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Calling function pointer to main program
> On Jan 3, 2020, at 11:35 AM, Jonas Maebe wrote:
>
> Additionally, you will also have to link in an object/library that does
> define a regular "main" function. And note that this will only work on
> libc-based targets (afaik only Darwin, Solaris, and AIX at this point).
So there needs to be a function named "main" that is linked to directly or can
it just be in a unit? I tried doing this but still get linker errors (tested on
MacOS of course). My example program is below.
It's possible I think -XM does something it doesn't also so here's is the main
function for the SDL/ios bindings. Note how UIApplicationMain is called which
then never returns control until the program exists. After that within the iOS
event handlers a call is made to SDL_main (see the external definition) which
if I understand correctly is set using -XP and this then in turn calls the
begin..end block of the main Pascal program. Is that correct?
extern C_LINKAGE int SDL_main(int argc, char *argv[]);
int main(int argc, char **argv)
{
int i;
/* store arguments */
forward_argc = argc;
forward_argv = (char **)malloc((argc+1) * sizeof(char *));
for (i = 0; i < argc; i++) {
forward_argv[i] = malloc( (strlen(argv[i])+1) * sizeof(char));
strcpy(forward_argv[i], argv[i]);
}
forward_argv[i] = NULL;
/* Give over control to run loop, SDLUIKitDelegate will handle most things
from here */
@autoreleasepool {
UIApplicationMain(argc, argv, nil, [SDLUIKitDelegate
getAppDelegateClassName]);
}
/* free the memory we used to hold copies of argc and argv */
for (i = 0; i < forward_argc; i++) {
free(forward_argv[i]);
}
free(forward_argv);
return exit_status;
}
Later on in the event handler called from UIApplicationMain:
// call the user program main function so they can enter their own event loop
logic
exit_status = SDL_main(forward_argc, forward_argv);
=
here is my test case:
fpc main.pas -XMuser_main
unit umain;
interface
uses
ctypes;
function user_main(argc: cint; argv: pchar): cint; cdecl; external;
function main(argc: cint; argv: pchar): cint;
implementation
function main(argc: cint; argv: pchar): cint;
begin
result := user_main(args, args);
end;
end.
program main;
uses
umain;
begin
writeln('called user main');
end.
The linker error I can't get past:
Undefined symbols for architecture x86_64:
"_main", referenced from:
start in crt1.10.5.o
(maybe you meant: _user_main)
Regards,
Ryan Joseph
___
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Re: [fpc-pascal] Calling function pointer to main program
On 03/01/2020 18:33, Ryan Joseph via fpc-pascal wrote: >> On Jan 2, 2020, at 2:57 PM, Ryan Joseph wrote: >> >> extern C_LINKAGE int SDL_main(int argc, char *argv[]); >> >> which they call from within the iOS event loop and that calls the programs >> main functions which was defined using -XMSDL_main > I still can't figure out how -XM works. Can anyone provide an example? When > ever I try to use it I get linker errors. > > I've basically just started with a trimmed down program that does nothing but > define an external new main function (like SDL does). From the SDL sources I > thought that it would now point to the main program body but I can't get past > linker errors. > > fpc main.pas -XMuser_main > > > > Undefined symbols for architecture x86_64: > "_P$TEST_$$_USER_MAIN$LONGINT$PCHAR$$LONGINT", referenced from: > _PASCALMAIN in main.o > "_main", referenced from: > start in crt1.10.5.o > (maybe you meant: _user_main) > > > program test; > uses > ctypes; > > function user_main(argc: cint; argv: pchar): cint; external; You're missing a "cdecl;" here. > begin > user_main(0,''); > end. Additionally, you will also have to link in an object/library that does define a regular "main" function. And note that this will only work on libc-based targets (afaik only Darwin, Solaris, and AIX at this point). Jonas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Calling function pointer to main program
> On Jan 2, 2020, at 2:57 PM, Ryan Joseph wrote: > > extern C_LINKAGE int SDL_main(int argc, char *argv[]); > > which they call from within the iOS event loop and that calls the programs > main functions which was defined using -XMSDL_main I still can't figure out how -XM works. Can anyone provide an example? When ever I try to use it I get linker errors. I've basically just started with a trimmed down program that does nothing but define an external new main function (like SDL does). From the SDL sources I thought that it would now point to the main program body but I can't get past linker errors. fpc main.pas -XMuser_main Undefined symbols for architecture x86_64: "_P$TEST_$$_USER_MAIN$LONGINT$PCHAR$$LONGINT", referenced from: _PASCALMAIN in main.o "_main", referenced from: start in crt1.10.5.o (maybe you meant: _user_main) program test; uses ctypes; function user_main(argc: cint; argv: pchar): cint; external; begin user_main(0,''); end. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Calling function pointer to main program
> On Jan 2, 2020, at 2:51 PM, Sven Barth via fpc-pascal > wrote: > > What exactly are you trying to accomplish on which platform with which > version? > I'm making an iOS platform layer in the style of SDL which needs to use iOS's main loop which never returns until the program stops execution. Within the iOS callbacks I need to then callback into the programs main begin..end block so the user can establish their own event loop (which then uses threads to synch between the 2 event loops). I've got the SDL source code but I'm not understanding how they get control back to the user even using the -XM flag. They have a function: extern C_LINKAGE int SDL_main(int argc, char *argv[]); which they call from within the iOS event loop and that calls the programs main functions which was defined using -XMSDL_main Sorry if that doesn't make sense but I barely understand the problem myself. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Calling function pointer to main program
Ryan Joseph via fpc-pascal schrieb am Do., 2. Jan. 2020, 18:11: > I need to override the main program function and then call back the main > program later. I know I can use -XM to set another function name besides > "main" but then how do I call back the original function "main" later? > What exactly are you trying to accomplish on which platform with which version? Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Calling function pointer to main program
> I know I can use -XM to set another function name besides "main" but then how do I call back the original function "main" later? I quickly analyze the generated assembly when you don't pass -XM: .globl main .type main,@function main: .globl PASCALMAIN .type PASCALMAIN,@function PASCALMAIN: vs when you do (-XMmymain): .globl mymain .type mymain,@function mymain: .globl PASCALMAIN .type PASCALMAIN,@function PASCALMAIN: so basically the original main does nothing and jump straight to PASCALMAIN, which is always there. So you can make your own main in a separate file that must be linked in during linking which calls whatever name you pass to -XM. -- Sent from: http://free-pascal-general.1045716.n5.nabble.com/ ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
[fpc-pascal] Calling function pointer to main program
I need to override the main program function and then call back the main program later. I know I can use -XM to set another function name besides "main" but then how do I call back the original function "main" later? Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
