On Thursday 09 October 2025 16:07:34 Martin Storsjö wrote:
> On Sun, 5 Oct 2025, Pali Rohár wrote:
>
> > msvcrt and UCRT function _chsize() has same behavior and also ABI as POSIX
> > function ftruncate() with 32-bit length.
> >
> > For 64-bit length msvcr80+ and UCRT provide function _chksize_s() but it
> > has slightly different usage as _chksize() / ftruncate() and so cannot be
> > directly aliased at symbol ABI level.
> >
> > Function _chksize_s() calls invalid parameter exception handler and return
> > value is errno.
> >
> > mingw-w64 currently provides its own ftruncate64() implementation which is
> > statically linked into every binary which calls ftruncate64().
> >
> > For msvcr80+ and UCRT builds, provide a new ftruncate64() implementation as
> > a simple wrapper around the CRT _chksize_s() function. To prevent calling
> > invalid parameter exception handler, validate input parametes manually
> > before calling the function itself.
> >
> > For pre-msvcr80 builds use the existing mingw-w64 implemenation of
> > ftruncate64() function.
> >
> > And for OS-system msvcrt.dll builds use either the _chksize_s() or the
> > mingw-w64 implemation. Function symbol _chksize_s in msvcrt.dll is
> > available since Windows Vista, so for x86/x64 builds, resolve that symbol
> > at runtime.
> >
> > Note that OS-system msvcrt.dll _chksize_s() does not call invalid parameter
> > exception handler, so call function directly without validation.
> >
> > To prevent symbol conflicts between existing mingw-w64 implementation of
> > ftruncate64 and new wrapper implementation (around _chksize_s), rename the
> > existing mingw-w64 implementation to __mingw_ftruncate64.
> >
> > With this change, calling the ftruncate64 function symbol results in using
> > the native _chksize_s CRT implementation for msvcr80+ and UCRT builds.
> > ---
> > mingw-w64-crt/Makefile.am | 5 +-
> > .../{ftruncate64.c => mingw_ftruncate64.c} | 6 ++-
> > mingw-w64-crt/stdio/msvcr80plus_ftruncate64.c | 30 ++++++++++++
> > mingw-w64-crt/stdio/msvcrtos_ftruncate64.c | 47 +++++++++++++++++++
> > 4 files changed, 86 insertions(+), 2 deletions(-)
> > rename mingw-w64-crt/stdio/{ftruncate64.c => mingw_ftruncate64.c} (98%)
> > create mode 100644 mingw-w64-crt/stdio/msvcr80plus_ftruncate64.c
> > create mode 100644 mingw-w64-crt/stdio/msvcrtos_ftruncate64.c
> >
> > diff --git a/mingw-w64-crt/Makefile.am b/mingw-w64-crt/Makefile.am
> > index 705624635acf..ca3e85264172 100644
> > --- a/mingw-w64-crt/Makefile.am
> > +++ b/mingw-w64-crt/Makefile.am
> > @@ -363,6 +363,7 @@ src_msvcrt=\
> > secapi/wmemmove_s.c \
> > stdio/_ftelli64.c \
> > stdio/mingw_lock.c \
> > + stdio/msvcrtos_ftruncate64.c \
> > stdio/msvcr110pre_stat32.c \
> > stdio/msvcr110pre_stat64i32.c \
> > stdio/msvcr110pre_wstat32.c \
> > @@ -933,6 +934,7 @@ src_pre_msvcr80=\
> > stdio/_stat64i32.c \
> > stdio/_wstat64i32.c \
> > stdio/mingw_lock.c \
> > + stdio/msvcr80pre_ftruncate64.c \
> > string/msvcr80pre_wcstok.c
>
> There's no msvcr80pre_ftruncate64.c included in this patchset.
>
> // Martin
Ou, I really forgot to git add it. Here is the missing part:
fixup! crt: Provide ftruncate64 function via wrapper around native CRT function
_chsize_s
diff --git a/mingw-w64-crt/stdio/msvcr80pre_ftruncate64.c
b/mingw-w64-crt/stdio/msvcr80pre_ftruncate64.c
new file mode 100644
index 000000000000..d0c983f66e56
--- /dev/null
+++ b/mingw-w64-crt/stdio/msvcr80pre_ftruncate64.c
@@ -0,0 +1,14 @@
+/**
+ * This file has no copyright assigned and is placed in the Public Domain.
+ * This file is part of the mingw-w64 runtime package.
+ * No warranty is given; refer to the file DISCLAIMER.PD within this package.
+ */
+
+#include <unistd.h>
+
+int __cdecl __mingw_ftruncate64(int fd, _off64_t length);
+
+int __cdecl ftruncate64(int fd, _off64_t length)
+{
+ return __mingw_ftruncate64(fd, length);
+}
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