[G4:~/testgpcadriaan] adriaan% cat NoUnderscore.p
program NoUnderscore;
procedure _Run; begin writeln('_Run') end;
begin _Run end.
[G4:~/testgpcadriaan] adriaan% gpc NoUnderscore.p NoUnderscore.p:4: warning: identifiers should not start with an underscore
[G4:~/testgpcadriaan] adriaan% gpc NoUnderscore.p -Wno-underscore
[G4:~/testgpcadriaan] adriaan% gpc NoUnderscore.p --gnu-pascal -Wno-underscore NoUnderscore.p:4: warning: identifiers should not start with an underscore
So, it seems that -Wno-underscore is broken when used with --gnu-pascal.
Regards,
Adriaan van Os