Re: [fpc-pascal] memory allocation of dynamic array

[Jonas Maebe]

On 23 Sep 2007, at 05:18, Marc Santhoff wrote:


My question:
In which cases will it happen that the memory of a dynamic array is
fragmented into multiple non-contiguous blocks?


Even if the current implementation allocates dynamic arrays always in  
one block (I think it does, but I'm not certain), there is probably  
no guarantee it will stay that way forever (and counting on that may  
consequently break your program in the future).


Counting on implementation details of opaque entities (such as set  
formats, anything regarding reference counted types such as when  
references are added or removed and when how many references will  
exist, rtti format, code generation details such as evaluation order  
of parameters or operands, memory manager allocation behaviour, ...)  
is almost 100% guaranteed to break your code at one point or another  
in time (and often at multiple points in time).



Jonas
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Re: [fpc-pascal] memory allocation of dynamic array

[mm]

Jonas Maebe a écrit :

Counting on implementation details of opaque entities (such as set 
formats, anything regarding reference counted types such as when 
references are added or removed and when how many references will exist, 
rtti format, code generation details such as evaluation order of 
parameters [...]


What do you mean with "evaluation order of parameters"?

mm
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Re: [fpc-pascal] memory allocation of dynamic array

[Florian Klaempfl]

mm schrieb:
> Jonas Maebe a écrit :
> 
>> Counting on implementation details of opaque entities (such as set
>> formats, anything regarding reference counted types such as when
>> references are added or removed and when how many references will
>> exist, rtti format, code generation details such as evaluation order
>> of parameters [...]
> 
> What do you mean with "evaluation order of parameters"?

When doing

f(f1(1),f2(2));

there are no assumptions possible if the compiler calls first f1 or f2.
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Re: [fpc-pascal] memory allocation of dynamic array

[Jonas Maebe]

On 24 Sep 2007, at 14:12, mm wrote:


Jonas Maebe a écrit :

Counting on implementation details of opaque entities (such as set  
formats, anything regarding reference counted types such as when  
references are added or removed and when how many references will  
exist, rtti format, code generation details such as evaluation  
order of parameters [...]


What do you mean with "evaluation order of parameters"?


var
  a: longint;

function f: longint;
begin
  result:=a;
  a:=a+1;
end;

procedure test(a,b: longint);
begin
  writeln(a,' ',b);
end;

begin
  a:=1;
  test(f,f);
end.


The above program can write either "1 2" or "2 1", and what it writes  
out can change between different compiler versions, platforms and  
optimization levels (i.e., the parameter evaluation order is undefined).



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Re: [fpc-pascal] Compiler 2.20 for Arm

[Carsten Bager]

> Try to build with -s and examine/post the ppas.sh and link.res file.

This is how the ppas.sh and the link.res file looks like. To me it looks ok.
Do you think it is an error in the linker.

Carsten


#!/bin/sh
DoExitAsm ()
{ echo "An error occurred while assembling $1"; exit 1; }
DoExitLink ()
{ echo "An error occurred while linking $1"; exit 1; }
echo Assembling testthreads
/Fpc/ArmBin/as -o threads.o threads.s
if [ $? != 0 ]; then DoExitAsm testthreads; fi
rm threads.s
echo Linking threads
/Fpc/ArmBin/ld   -Map=link.map -dynamic-linker=/lib/ld-linux.so.2  --gc-
sections  -L. -o threads link.res
if [ $? != 0 ]; then DoExitLink threads; fi



SEARCH_DIR(/Fpc/Pas/ReleasedUnits/LibArm9/)
SEARCH_DIR(/Fpc/Lib/Ulibc/Arm/)
SEARCH_DIR(/Fpc/Lib/2.2.0/arm-linux/Fpc/)
SEARCH_DIR(/Fpc/Pas/ReleasedUnits/PpuArm9/)
SEARCH_DIR(/Fpc/ArmBin/)
INPUT(
/Fpc/Lib/Ulibc/Arm/cprt0.o
threads.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/system.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/lineinfo.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/strings.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/objpas.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/cthreads.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/sysutils.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/dos.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/baseunix.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/unix.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/unixtype.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/initc.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/dl.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/unixutil.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/syscall.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/ctypes.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/errors.o
/Fpc/Lib/2.2.0/arm-linux/Fpc/sysconst.o
)
INPUT(
-lulibc
-lgcc_s
-lpthread
-ldl
-lc
)
ENTRY(_start)

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