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Ensure the entrypoint is taken into account when computing the export table #146

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6193045
Split imports and link_obj
dra27 Nov 21, 2024
6788305
Include default libraries in defined_in
dra27 Nov 21, 2024
84f24a3
Choose the correct startup object for mingw-w64
dra27 Nov 21, 2024
e586caf
Consider the entrypoint when determining exports
dra27 Nov 21, 2024
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3 changes: 3 additions & 0 deletions CHANGES
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,9 @@ Version 0.44
as querying the compilers for their library search paths. Support parsing
clang output.
(Antonin Décimo, review by David Allsopp)
- GPR#146: Take the entrypoint (main, wmainCRTStartup, etc.) into account when
determining the modules which will be linked. For mingw-w64, select crt2u.o
instead of crt2.o if -link -municode is specified (David Allsopp)
Comment on lines +40 to +42

@MisterDA MisterDA Jul 22, 2026

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This should be moved in the section above.


Version 0.43
- GPR#108: Add -lgcc_s to Cygwin's link libraries, upstreaming a patch from the
Expand Down
149 changes: 110 additions & 39 deletions reloc.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -725,7 +725,7 @@ let needed imported defined resolve_alias resolve_alternate obj =
StrSet.empty
obj.symbols

let build_dll link_exe output_file files exts extra_args =
let build_dll link_exe output_file files exts extra_args_string =
let main_pgm = link_exe <> `DLL in

(* fully resolve filenames, eliminate duplicates *)
Expand Down Expand Up @@ -767,7 +767,7 @@ let build_dll link_exe output_file files exts extra_args =
in
(* Collect all the available symbols, including those defined
in default libraries *)
let defined, from_imports, resolve_alias, resolve_alternate =
let defined, from_imports, resolve_alias, resolve_alternate, collected =
let aliases = Hashtbl.create 16 in
let alternates = Hashtbl.create 16 in
let defined = ref StrSet.empty in
Expand Down Expand Up @@ -836,14 +836,16 @@ let build_dll link_exe output_file files exts extra_args =

and collect_file fn =
if not (Hashtbl.mem collected (String.lowercase_ascii fn)) then begin
Hashtbl.replace collected (String.lowercase_ascii fn) ();
debug 2 "** open: %s" fn;
collect_defined fn (Lib.read fn)
end

and collect_defined fn = function
| `Obj obj -> collect_defined_obj obj
| `Obj obj ->
Hashtbl.replace collected (String.lowercase_ascii fn) [fn, obj];
collect_defined_obj obj
| `Lib (objs,imports) ->
Hashtbl.replace collected (String.lowercase_ascii fn) objs;
List.iter (fun (_, obj) -> collect_defined_obj obj) objs;
List.iter
(fun (s,_) ->
Expand All @@ -854,12 +856,7 @@ let build_dll link_exe output_file files exts extra_args =
)
imports
in
List.iter
(fun (fn,x) ->
Hashtbl.replace collected (String.lowercase_ascii fn) ();
collect_defined fn x
)
files;
List.iter (fun (fn,x) -> collect_defined fn x) files;
if !use_default_libs then List.iter (fun fn -> collect_file (find_file fn)) !default_libs;
List.iter (fun fn -> collect_file (find_file fn)) exts;

Expand All @@ -869,13 +866,13 @@ let build_dll link_exe output_file files exts extra_args =
if !machine = `x64 then add_def "__ImageBase"
else add_def "___ImageBase";

!defined, !from_imports, (Hashtbl.find aliases), (Hashtbl.find alternates)
!defined, !from_imports, (Hashtbl.find aliases), (Hashtbl.find alternates), collected
in

(* Determine which objects from the given libraries should be linked
in. First step: find the mapping (symbol -> object) for these
objects. *)
let defined_in =
let defined_in, default_libs =
let defined_in = Hashtbl.create 16 in
let def_in_obj fn (objname, obj) =
List.iter
Expand All @@ -893,29 +890,36 @@ let build_dll link_exe output_file files exts extra_args =
)
obj.symbols
in
List.iter
(fun (fn,objs) ->
if !explain then Printf.printf "Scanning lib %s\n%!" fn;
List.iter (def_in_obj fn) objs
)
libs;
Hashtbl.find defined_in
let scan (fn,objs) =
if !explain then Printf.printf "Scanning lib %s\n%!" fn;
List.iter (def_in_obj fn) objs
in
let default_libs =
List.fold_right
(fun fn acc ->
let fn = find_file fn in
scan (fn, Hashtbl.find collected (String.lowercase_ascii fn));
StrSet.add fn acc)
(if !use_default_libs then !default_libs else [])
StrSet.empty
in
List.iter scan libs;
Hashtbl.find defined_in, default_libs
in

let imported_from_implib = ref StrSet.empty in
let imported = ref StrSet.empty in

let imports obj =
let n = needed imported defined resolve_alias resolve_alternate obj in
imported_from_implib := StrSet.union !imported_from_implib (StrSet.inter n from_imports);
let undefs = StrSet.diff n defined in
StrSet.filter
(fun s ->
match check_prefix "__imp_" s with
| Some _ -> false
| None -> s <> "environ" (* special hack for Cygwin64 *)
)
undefs
undefs, StrSet.inter n from_imports
in

(* Second step: transitive closure, starting from given objects *)
Expand Down Expand Up @@ -981,7 +985,7 @@ let build_dll link_exe output_file files exts extra_args =
in

let dll_exports = ref StrSet.empty in
let rec link_obj fn obj =
let record_exports obj =
List.iter
(fun sym ->
if Symbol.is_defin sym && exportable sym.sym_name
Expand All @@ -990,7 +994,9 @@ let build_dll link_exe output_file files exts extra_args =
obj.symbols;

dll_exports := List.fold_left (fun accu x -> StrSet.add x accu)
!dll_exports (collect_dllexports obj);
!dll_exports (collect_dllexports obj)
in
let rec link_obj fn obj =
StrSet.iter
(fun s ->
if StrSet.mem s !exported then ()
Expand All @@ -1007,16 +1013,75 @@ let build_dll link_exe output_file files exts extra_args =
(needed imported defined resolve_alias resolve_alternate obj)

and link_libobj (libname,objname,obj) =
let default = StrSet.mem libname default_libs in
if Hashtbl.mem libobjects (libname,objname) then ()
else (Hashtbl.replace libobjects (libname,objname) (obj,imports obj);
else (let imports, from_imports = imports obj in
let imports = if default then StrSet.empty else imports in
Hashtbl.replace libobjects (libname,objname) (obj,imports);
if not default then begin
imported_from_implib := StrSet.union !imported_from_implib from_imports;
record_exports obj
end;
link_obj (Printf.sprintf "%s(%s)" libname objname) obj)
in

let entrypoint =
if not main_pgm then
None
else
match !toolchain with
| `CYGWIN64 ->
Some "main"
| `MINGW | `MINGW64 -> begin
let entry_point s =
String.length s > 7 && String.sub s 0 7 = "-Wl,-e,"

@nojb nojb Jul 21, 2026

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Isn't -Wl,-e rewritten into -link arguments (cf

flexdll/cmdline.ml

Lines 281 to 285 in ab8161f

| s :: rest when String.length s >= 6 && String.sub s 0 5 = "-Wl,-" ->
let args =
String.split_on_char ',' (String.sub s 4 (String.length s - 4))
in
List.fold_right (fun arg args -> "-link" :: arg :: args) args (tr rest)
) ?

@dra27 dra27 Jul 22, 2026

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Urgh - good catch, and unfortunately it's because this part is completely broken. The problem here is that when we link MSVC we actually call the linker, but when we link mingw-w64, we call the C compiler! I added this bit here for completeness - for MSVC, we of course select Unicode with -link /entry:wmainCRTStartup and that works because flexlink passes the /entry: directly to /link. For mingw-w64, we of course do -link -municode and that survives being passed to the C compiler to do the linking, but -Wl,-e,foo won't work being passed to the C compiler as -e foo. I only added this handling for -Wl,-e because I just written the /entry: part for MSVC (which I knew was needed).

Hmm. Given that you can't specify the entry point at the moment on mingw-w64, I'm tempted to remove this bit of code and just add a comment that you can't change the entrypoint on mingw-w64?

@nojb nojb Jul 22, 2026

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Sounds reasonable!

@dra27 dra27 Jul 22, 2026

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Oh - coffee kicks in! I remember how this works - the -Wl, translation to -link is a shim to allow common options to pass through. You can specify the entry point on mingw-w64, it's just that you have to say -link -Wl,-e,entrypoint at which point the code above does work as intended!

in
try
let s = List.find entry_point !extra_args in
Some (String.sub s 7 (String.length s - 7))
with Not_found ->
Some "mainCRTStartup"
end
| `MSVC | `MSVC64 -> begin
let entry_point s =
String.length s > 7 && String.lowercase_ascii (String.sub s 0 7) = "/entry:"
in
try
let s = List.find entry_point !extra_args in
Some (String.sub s 7 (String.length s - 7))
with Not_found ->
if !subsystem = "windows" then
Some "WinMainCRTStartup"
else
Some "mainCRTStartup"
end
| `LIGHTLD | `GNAT | `GNAT64 ->
None
in
let () =
match entrypoint with
| None -> ()
| Some entrypoint ->
try
let (libname, objname, _) as o = defined_in entrypoint in
if !explain then
Printf.printf "%s(%s) because of entrypoint %s\n%!" libname objname
entrypoint;
link_libobj o
with Not_found ->
if !explain then
Printf.printf "Entrypoint %s not found\n%!" entrypoint
in
let redirect = Hashtbl.create 16 in
List.iter
(fun (fn, obj) ->
let default = StrSet.mem fn default_libs in
let imps, from_imports = imports obj in
if not default then begin
imported_from_implib := StrSet.union !imported_from_implib from_imports;
record_exports obj
end;
link_obj fn obj;
let imps = imports obj in
if StrSet.is_empty imps then ()
else Hashtbl.replace redirect fn (close_obj fn imps obj);
) objs;
Expand Down Expand Up @@ -1142,24 +1207,24 @@ let build_dll link_exe output_file files exts extra_args =
being an empty file. *)
let c = open_out implib in output_string c "x"; close_out c;
let _impexp = add_temp (Filename.chop_suffix implib ".lib" ^ ".exp") in
let extra_args =
if !custom_crt then "/nodefaultlib:LIBCMT /nodefaultlib:MSVCRT " ^ extra_args
else "msvcrt.lib " ^ extra_args
let extra_args_string =
if !custom_crt then "/nodefaultlib:LIBCMT /nodefaultlib:MSVCRT " ^ extra_args_string
else "msvcrt.lib " ^ extra_args_string
in

let extra_args =
if !machine = `x64 then (Printf.sprintf "/base:%s " !base_addr) ^ extra_args else extra_args
let extra_args_string =
if !machine = `x64 then (Printf.sprintf "/base:%s " !base_addr) ^ extra_args_string else extra_args_string
in

let extra_args =
let extra_args_string =
(* FlexDLL doesn't process .voltbl sections correctly, so don't allow the linker
to process them. *)
let command =
if Sys.win32 then link ^ " /nologo /? | findstr EMITVOLATILEMETADATA > NUL"
else link ^ " /nologo '/?' | grep -iq emitvolatilemetadata >/dev/null" in
if Sys.command command = 0 then
"/EMITVOLATILEMETADATA:NO " ^ extra_args
else extra_args
"/EMITVOLATILEMETADATA:NO " ^ extra_args_string
else extra_args_string
in

(* Flexdll requires that all images (main programs and all the DLLs) are
Expand Down Expand Up @@ -1187,7 +1252,7 @@ let build_dll link_exe output_file files exts extra_args =
(Filename.quote output_file)
!subsystem
files descr
extra_args
extra_args_string
| `CYGWIN64 ->
let def_file =
if main_pgm then ""
Expand All @@ -1209,7 +1274,7 @@ let build_dll link_exe output_file files exts extra_args =
descr
files
def_file
extra_args
extra_args_string
| `MINGW | `MINGW64 | `GNAT | `GNAT64 ->
let def_file =
if main_pgm then ""
Expand All @@ -1233,7 +1298,7 @@ let build_dll link_exe output_file files exts extra_args =
files
def_file
(if !implib then "-Wl,--out-implib=" ^ Filename.quote (Filename.chop_extension output_file ^ ".a") else "")
extra_args
extra_args_string
| `LIGHTLD ->
no_merge_manifest := true;
let ld = Option.value !Cmdline.use_linker ~default:"ld" in
Expand All @@ -1246,7 +1311,7 @@ let build_dll link_exe output_file files exts extra_args =
descr
files
(if !implib then "--out-implib " ^ Filename.quote (Filename.chop_extension output_file ^ ".a") else "")
extra_args
extra_args_string
in
debug ~dry_mode 1 "+ %s" cmd;
if not !dry_mode then begin
Expand Down Expand Up @@ -1423,8 +1488,14 @@ let setup_toolchain () =
with Not_found -> ()
in
default_libs := "-lmingw32" :: "-lgcc" :: !default_libs;
if !exe_mode = `EXE then default_libs := "crt2.o" :: !default_libs
else default_libs := "dllcrt2.o" :: !default_libs
if not (List.mem "-nostartfiles" !extra_args) then begin
if !exe_mode = `EXE then
if List.mem "-municode" !extra_args then
default_libs := "crt2u.o" :: !default_libs
else
default_libs := "crt2.o" :: !default_libs
else default_libs := "dllcrt2.o" :: !default_libs
end
in
match !toolchain with
| _ when !builtin_linker ->
Expand Down