From: David Laight Date: Mon, 2 Mar 2026 10:17:56 +0000 (+0000) Subject: selftests/nolibc: check vsnprintf() output buffer before the length X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=9aa8a4afd4e6407a4d4521c325855c4467a88b73;p=thirdparty%2Fkernel%2Flinux.git selftests/nolibc: check vsnprintf() output buffer before the length Check the string matches before checking the returned length. Only print the string once when it matches. Makes it a lot easier to diagnose any incorrect output. Signed-off-by: David Laight Acked-by: Willy Tarreau Link: https://patch.msgid.link/20260302101815.3043-5-david.laight.linux@gmail.com Signed-off-by: Thomas Weißschuh --- diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c index 7588212df1248..bfe793caa9637 100644 --- a/tools/testing/selftests/nolibc/nolibc-test.c +++ b/tools/testing/selftests/nolibc/nolibc-test.c @@ -1676,25 +1676,27 @@ static int expect_vfprintf(int llen, int c, const char *expected, const char *fm char buf[100]; va_list args; ssize_t w; - int ret; - va_start(args, fmt); /* Only allow writing 21 bytes, to test truncation */ w = vsnprintf(buf, 21, fmt, args); va_end(args); + llen += printf(" \"%s\"", buf); + if (strncmp(expected, buf, c)) { + llen += printf(" should be \"%s\"", expected); + result(llen, FAIL); + return 1; + } + if (w != c) { llen += printf(" written(%d) != %d", (int)w, c); result(llen, FAIL); return 1; } - llen += printf(" \"%s\" = \"%s\"", expected, buf); - ret = strncmp(expected, buf, c) != 0; - - result(llen, ret ? FAIL : OK); - return ret; + result(llen, OK); + return 0; } static int test_scanf(void)