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commit    b48ae226e6c31f5e1801e626d7602be7969f0fbd
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Oct 13 21:56:45 2025 +0000
First released in: 13.23, 14.20, 15.15, 16.11, 17.7, 18.1

    Fix incorrect message-printing in win32security.c.
    
    log_error() would probably fail completely if used, and would
    certainly print garbage for anything that needed to be interpolated
    into the message, because it was failing to use the correct printing
    subroutine for a va_list argument.
    
    This bug likely went undetected because the error cases this code
    is used for are rarely exercised - they only occur when Windows
    security API calls fail catastrophically (out of memory, security
    subsystem corruption, etc).
    
    The FRONTEND variant can be fixed just by calling vfprintf()
    instead of fprintf().  However, there was no va_list variant
    of write_stderr(), so create one by refactoring that function.
    Following the usual naming convention for such things, call
    it vwrite_stderr().
    
    Author: Bryan Green <dbryan.green@gmail.com>
    Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
    Discussion: https://postgr.es/m/CAF+pBj8goe4fRmZ0V3Cs6eyWzYLvK+HvFLYEYWG=TzaM+tWPnw@mail.gmail.com
    Backpatch-through: 13


 src/backend/utils/error/elog.c | 16 +++++++++++++---
 src/include/utils/elog.h       |  1 +
 src/port/win32security.c       |  4 ++--
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index dc0b74dc30b..d78f3ab8a30 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -3783,13 +3783,24 @@ write_stderr(const char *fmt,...)
 {
 	va_list		ap;
 
+	va_start(ap, fmt);
+	vwrite_stderr(fmt, ap);
+	va_end(ap);
+}
+
+
+/*
+ * Write errors to stderr (or by equal means when stderr is
+ * not available) - va_list version
+ */
+void
+vwrite_stderr(const char *fmt, va_list ap)
+{
 #ifdef WIN32
 	char		errbuf[2048];	/* Arbitrary size? */
 #endif
 
 	fmt = _(fmt);
-
-	va_start(ap, fmt);
 #ifndef WIN32
 	/* On Unix, we just fprintf to stderr */
 	vfprintf(stderr, fmt, ap);
@@ -3812,5 +3823,4 @@ write_stderr(const char *fmt,...)
 		fflush(stderr);
 	}
 #endif
-	va_end(ap);
 }
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 675f4f5f469..581b39091e0 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -527,5 +527,6 @@ extern void write_jsonlog(ErrorData *edata);
  * safely (memory context, GUC load etc)
  */
 extern void write_stderr(const char *fmt,...) pg_attribute_printf(1, 2);
+extern void vwrite_stderr(const char *fmt, va_list ap) pg_attribute_printf(1, 0);
 
 #endif							/* ELOG_H */
diff --git a/src/port/win32security.c b/src/port/win32security.c
index a46b82dd048..b7608ab1706 100644
--- a/src/port/win32security.c
+++ b/src/port/win32security.c
@@ -31,9 +31,9 @@ log_error(const char *fmt,...)
 
 	va_start(ap, fmt);
 #ifndef FRONTEND
-	write_stderr(fmt, ap);
+	vwrite_stderr(fmt, ap);
 #else
-	fprintf(stderr, fmt, ap);
+	vfprintf(stderr, fmt, ap);
 #endif
 	va_end(ap);
 }


[parent: f691e72585a3]