And for notice, I have disabled -CX and -XX
W dniu 22.07.2026 o 16:09, Dibo via fpc-pascal pisze:
Hi,
I suspect that my first message was blocked because I attached ODT
document. Please ignore duplicate if it show up.
I mentioned about this issue some time ago in the topic about PasFLTK
bindings which I made. I decided to make dedicated thread because it
seems to be interesting.
So. I'm developing PasFLTK bindings for CFLTK which is flatten C
binding for major FLTK UI framework written in C++. PasFLTK has two
modes, shared library which work perfectly fine and experimental
static linking.
Static linking has issues which I'm consistently fixing. Major problem
is that C++ classes are not initialized in proper way. Problem is not
a matter of "Static Initialization Order Fiasco" because CFLTK/FLTK is
designed to be static linking for default (and that is how other
language bindings are using it). Problem is how FPC LD linker prepare
"startup" routines. For example:
Class Fl_File_Chooser2.cxx has this public variable:
const char *Fl_File_Chooser::filesystems_label =
Fl::system_driver()->filesystems_label();
System_driver is not initialized yet so filesystems_label become null
which result with access violations. Since I'm linux user I started
from this platform, working on this with Claude AI (which amazed me
how deeply he can analyze binaries on low level). On linux, fix was
small and easy (for Claude, not for me of course). LD linker prepare
wrong init structure and doesn't call the __init_array_start in linux
ELF standard. So patch looks like that:
type
TCtorProc = procedure(); cdecl;
PCtorProc = ^TCtorProc;
var
__init_array_start: Byte; external name '__init_array_start';
__init_array_end: Byte; external name '__init_array_end';
procedure RunCppGlobalConstructorsLinux;
var
p, pend: PCtorProc;
begin
p := PCtorProc(@__init_array_start);
pend := PCtorProc(@__init_array_end);
while p < pend do
begin
if Assigned(p^) then
p^();
Inc(p);
end;
end;
That small piece of code fixed everything and static linking work like
a charm on linux. I have project (which I publish soon) totally
written as static linking and didn't notice any new issues so far.
Now windows version. Here complication start. First, build-in FPC
linker is useless and throw error:
Error: Failed reading coff file, invalid section index while reading
C:\Users\vboxuser\Documents\CFLTKlibs\libcfltk.a(cfl_window.cpp.obj)
I had to use -Xe flag which switch to external ld.exe linker. But then
I had DWARF errors because LD support only up to 4 version and my
MinGW toolchain (MSYS2 on windows) is using ver. 5. I had to call
`strip --strip-debug` on all *.a files (including some MinGW - e.g
libstd++.a).
Now, when binding are compiling fine, I fall to the same problem with
initialization as on linux. I spent few evenings with Claude on this.
We compared objdump -h and extracted objects on exactly the same demos
written line by line one using C (CFLTK) and second Free Pascal. Since
linux use ELF we get __init_array_start, on windows PE - it looks
harder. LD.exe delivered with FPC is quite old and doesn't use modern
standard. Demo written in C and linked by LD from toolchain has
correct .ctors and __CTOR_LIST__ which FPC ld.exe is missing (in fact,
filling it incorrectly). Tried using -FD"C:\msys64\mingw64\bin" which
load ld.exe from MinGW toolchain but this result with dozens errors:
C:\msys64\mingw64\bin\ld.exe:
C:\programowanie\lazarus\fpc\3.2.2\units\x86_64-win64\rtl\sysutils.o:
illegal relocation type 0 at address 0
C:\msys64\mingw64\bin\ld.exe:
C:\programowanie\lazarus\fpc\3.2.2\units\x86_64-win64\rtl\math.o:
illegal relocation type 0 at address 0
Claude also compared rust bindings for CFLTK because it also use
static linking. They had also problems and are stick to the specific
toolchain. But there problem was easier to fix because Rust linker
correctly linking crt2.o and has own guardians rsbegin.o and rsend.o
(equivalent of crtbegin.o and crtend.o) which are missing in FPC ld
linker.
Finally I get it working with Claude but this require reorganize *.a
and C++ objects with --globalize-symbol and this solution is not
acceptable for me because it require engagement everytime when
something changed in CFLT/FLTK source or even in MinGW.
I'll be not writting anymore and just attach summary of our work which
I asked Claude to write in short. It has more technical details. To
sum up. Is there any plans to upgrade LD linker or exists any alpha /
beta of upcoming release? The difference between FPC ld and GCC ld is
almost 10 years. I read somewhere that FPC is not designed to link C++
(only C) but as we can see, it could be just small step to make it
possible and that open huge door.
Below is Claude's summary.
Regards, Dibo.
Environment:
Free Pascal Compiler 3.2.2, Windows target x86_64-win64
Bundled linker:
C:\programowanie\lazarus\fpc\3.2.2\bin\x86_64-win64\ld.exe — GNU ld
(GNU Binutils) 2.28
Comparison linker: ld.exe from MSYS2 mingw-w64-x86_64-binutils
package, located at C:\msys64\mingw64\bin\ld.exe — GNU ld (GNU
Binutils) 2.46.1
GCC/G++ used to build FLTK, CFLTK, and the comparison C++ demo:
16.1.0 (MSYS2 mingw-w64-x86_64-gcc, reported as "GCC 16.1.0"
FLTK version: 1.4.5, CFLTK version: 1.5.23
Root cause identified: FPC 3.2.2's bundled ld.exe fails to correctly
merge .ctors input sections (containing C++ global constructor
pointers) from object files compiled by a modern GCC (16.1.0,
MinGW-w64/MSYS2) into the final __CTOR_LIST__ array — even though the
linker script (identical KEEP(*(.ctors)) rule, confirmed via ld.exe
--verbose on both linkers) is present in both the old bundled ld.exe
and a current MSYS2 ld.exe.
Evidence:
A raw hex dump of __CTOR_LIST__ in an FPC-linked executable (with
10 real global constructors from a statically-linked FLTK/CFLTK
library present and confirmed via nm) shows: sentinel (-1) immediately
followed by terminator (0) — zero constructor pointers, despite the
constructor functions (_GLOBAL__sub_I_*) physically existing in the
binary.
The same source compiled and linked natively with g++.exe/current
MSYS2 ld.exe produces a fully populated __CTOR_LIST__ with all 10
pointers correctly resolved to the matching _GLOBAL__sub_I_* addresses.
Attempting to relink the FPC-built binary with the current MSYS2
ld.exe (via -FD<path>) fails with illegal relocation type 0 / invalid
section index errors on FPC's own RTL object files (sysutils.o,
math.o) — indicating FPC's internal object emitter and modern binutils
have diverged in mutually incompatible ways. rtl\sysutils.o: illegal
relocation type 0 at address 0 etc
The input .o files from the affected FLTK library use COMDAT
sections (LINK_ONCE_DISCARD) extensively (confirmed via objdump -h),
which may be related to how the old ld.exe mishandles their .ctors
content during merging — this is hypothesis
Consequently, statically linking modern C++ libraries (FLTK/CFLTK,
built with current MinGW-w64/GCC) into an FPC/Lazarus Windows
executable silently drops all global C++ constructors, causing use of
uninitialized static objects downstream (observed as intermittent
access violations depending on which code paths touch affected statics).
Workaround currently used: manually enumerating _GLOBAL__sub_I_*
symbols via nm on the linked (even if crashing) executable,
globalizing their linkage scope via objcopy --globalize-symbol (they
are emitted as local/t symbols), and generating a small Pascal unit
that calls them all explicitly at program startup. This resolves some
but not all downstream issues, suggesting missing constructor
invocation is necessary but possibly not sufficient — full
mainCRTStartup context (TLS/locale/guard-variable state) may also
matter for some lazily-initialized C++ singletons. - this is last
hypothesis
Question for the list: Is there a newer/beta ld.exe (or plan to update
the bundled binutils) for the Windows FPC toolchain that correctly
handles .ctors/COMDAT sections as emitted by current GCC, without
breaking compatibility with FPC's own object file emitter?
_______________________________________________
fpc-pascal maillist [email protected]
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
_______________________________________________
fpc-pascal maillist - [email protected]
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
