[PATCH] Cygwin: Fix error return for madvise()

Currently madvise() and posix_madvise() are wired together as one
function: the latter.  But their error returns should be different.
Make madvise a first-class export in cygwin.din; code a new madvise()
that calls posix_madvise() and massages any error return.

Reported-by: Christian Franke <[email protected]>
Addresses: https://cygwin.com/pipermail/cygwin/2026-July/259872.html
Signed-off-by: Mark Geisert <[email protected]>
Fixes: 61522196c715 (* Merge in cygwin-64bit-branch.)

---
 winsup/cygwin/cygwin.din               |  2 +-
 winsup/cygwin/include/cygwin/version.h |  3 ++-
 winsup/cygwin/mm/mmap.cc               | 12 ++++++++++++
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/cygwin.din b/winsup/cygwin/cygwin.din
index 2e53bc819..937eacdaf 100644
--- a/winsup/cygwin/cygwin.din
+++ b/winsup/cygwin/cygwin.din
@@ -951,7 +951,7 @@ lseek SIGFE
 lsetxattr SIGFE
 lstat SIGFE
 lutimes SIGFE
-madvise = posix_madvise SIGFE
+madvise SIGFE
 makecontext NOSIGFE
 mallinfo SIGFE
 malloc SIGFE
diff --git a/winsup/cygwin/include/cygwin/version.h b/winsup/cygwin/include/cygwin/version.h
index 71ac5282b..fc838e23e 100644
--- a/winsup/cygwin/include/cygwin/version.h
+++ b/winsup/cygwin/include/cygwin/version.h
@@ -502,12 +502,13 @@ details. */
   360: Add RLIMIT_NPROC.
   361: Export _Fork.
   362: Export C23 stdbit functions.
+  363: Export madvise separately from posix_madvise.
 
   Note that we forgot to bump the api for ualarm, strtoll, strtoull,
   sigaltstack, sethostname. */
 
 #define CYGWIN_VERSION_API_MAJOR 0
-#define CYGWIN_VERSION_API_MINOR 362
+#define CYGWIN_VERSION_API_MINOR 363
 
 /* There is also a compatibity version number associated with the shared memory
    regions.  It is incremented when incompatible changes are made to the shared
diff --git a/winsup/cygwin/mm/mmap.cc b/winsup/cygwin/mm/mmap.cc
index 1416e4ddc..93db9e474 100644
--- a/winsup/cygwin/mm/mmap.cc
+++ b/winsup/cygwin/mm/mmap.cc
@@ -1422,6 +1422,18 @@ munlock (const void *addr, size_t len)
   return ret;
 }
 
+extern "C" int
+madvise (void *addr, size_t len, int advice)
+{
+  int ret = posix_madvise (addr, len, advice);
+  if (ret > 0)
+    {
+      set_errno (ret);
+      ret = -1;
+    }
+  return ret;
+}
+
 extern "C" int
 posix_madvise (void *addr, size_t len, int advice)
 {
-- 
2.51.0