[fpc-devel]I suggest a new FPC feature
Michael Van Canneyt
michael.vancanneyt at wisa.be
Fri Oct 12 16:13:41 CEST 2001
On Fri, 12 Oct 2001, Jonas Maebe wrote:
> On vrijdag, oktober 12, 2001, at 10:30 , Pavel V. Ozerski wrote:
> > TestProc: pushl %ebp
> > movl %esp,%ebp
> > nop
> > popl %ebp
> > ret $0x0008
> > I see no saving ebx,esi,edi here. Btw, this obj file could be linked
> > not only to Delphi or CPPBuilder projects.
> That's because you didn't modify any either. Delphi expects you to save
> the necessary registers yourself when you use assembler.
> > But if I restore 'stdcall' keywords and compile unit with FPC 1.1,
> > saving registers will be added:
> > _DTEST2$$_TESTPROC$LONGINT$LONGINT:
> > pushl %ebp
> > movl %esp,%ebp
> > pushl %edi
> > pushl %esi
> > pushl %ebx
> > nop
> > popl %ebx
> > popl %esi
> > popl %edi
> > leave
> > ret $8
> FPC OTOH, expects that all registers are modified in an assembler
> statement, unless you specify the list of modified registers using the
> ['reg1','reg2'] notation at the end of the assembler procedure.
> > My yesterday's tests demonstrated that also for export procedures
> > Delphi 3.0 does not include saving registers into code.
> > Additionally, these tests demonstrate that default conventions which
> > uses FPC are not the same as wich uses FPC for
> > procedures wich have 'stdcall' keyword.
> This has nothing to do with differences in calling conventions, but with
> differences in assuming which registers are destroyed in an assembler
> block. Just include some real code which uses a lot of registers in your
> test procedure, and Delphi should save those registers too.
> >> Actually, stdcall is *the* standard calling convention for the 80x86
> > Then why Delphi does not save registers in stdcall procedures?
> See above, it assumes that you do that yourself when using assembler
> > I'm sure, it is not optimization issue : I added built-in-assember
> > instruction mov edi,eax into body
> > of stdcall procedure but Delphi 3 also did not save edi!
> Same reason as above.
> > Also if stdcall must save these registers then default calling
> > conventions in fpc are not true stdcall
> > and they should have a name.
> Default FPC calling conventions = "fpc calling conventions". They don't
> need a name currently, because we don't have a global switch to change
> the default calling convention. Is there a directive to select "default
> Delphi calling conventions" in Delphi?
No. Delphi uses register calling convention, unless specifically instructed
otherwise in the declaration.
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