From 8ea69373a42898a89c64df0fa731767cbeaba3dc Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Mon, 15 Jun 2026 11:52:23 +0000 Subject: [PATCH] compat/msvc: use _chsize_s for ftruncate On Windows, `unsigned long` and `long` are 32 bits even on 64-bit builds. The MSVC compatibility header has shimmed `ftruncate()` with #define ftruncate _chsize ever since `compat/msvc-posix.h` was introduced. `_chsize()` takes a 32-bit `long` for the new length, which silently truncates files (and the requested size) to 2 GiB. That is enough to make t7508 test 126 "git add fails gracefully with 4 GiB and 8 GiB files" fail under MSVC: `test-tool truncate` creates a sparse 4 GiB or 8 GiB file via the shimmed `ftruncate()`, and the test never gets off the ground. `_chsize_s()` is the modern replacement, accepts a 64-bit `__int64` length, and is the only sensible target on Windows. The catch is that it does not follow the POSIX `-1` + `errno` convention: it returns `0` on success and an errno value (a small positive integer) on failure. A plain `#define ftruncate _chsize_s` would therefore silently break callers that test the return value as `< 0` or against `-1`, of which there are several: `http.c`, `parallel-checkout.c`, and `t/helper/test-truncate.c` among them. Introduce a `static inline` wrapper that calls `_chsize_s()`, copies its errno return into `errno`, and translates the result to the familiar `-1` / `0` convention, then point `ftruncate` at the wrapper. Place the wrapper after `#include "mingw-posix.h"` so the `off_t` parameter resolves to the already-widened `off64_t` rather than the 32-bit `_off_t` from `compat/vcbuild/include/unistd.h`. MinGW is unaffected: its `ftruncate()` already takes `off_t` and routes through `ftruncate64()` when `_FILE_OFFSET_BITS=64`, which is the default in our build. Assisted-by: Opus 4.7 Signed-off-by: Johannes Schindelin Signed-off-by: Junio C Hamano --- compat/msvc-posix.h | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/compat/msvc-posix.h b/compat/msvc-posix.h index c500b8b4aa..7ce39b8d3f 100644 --- a/compat/msvc-posix.h +++ b/compat/msvc-posix.h @@ -16,7 +16,6 @@ #define __attribute__(x) #define strcasecmp _stricmp #define strncasecmp _strnicmp -#define ftruncate _chsize #define strtoull _strtoui64 #define strtoll _strtoi64 @@ -30,4 +29,27 @@ typedef int sigset_t; #include "mingw-posix.h" +/* + * MSVC's `_chsize()` takes a 32-bit `long` and silently truncates files + * to 2 GiB. `_chsize_s()` accepts a 64-bit length but returns 0 on + * success or an errno value on failure, rather than the -1/errno + * convention POSIX `ftruncate()` callers expect. Wrap it so callers + * that test the return value as `< 0` or against `-1` keep working. + * + * Note: this declaration must follow `#include "mingw-posix.h"` so + * `off_t` resolves to `off64_t` and the parameter type matches the + * underlying `_chsize_s()` width. + */ +static inline int msvc_ftruncate(int fd, off_t length) +{ + int err = _chsize_s(fd, length); + + if (err) { + errno = err; + return -1; + } + return 0; +} +#define ftruncate msvc_ftruncate + #endif /* COMPAT_MSVC_POSIX_H */