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selftests/nolibc: check vsnprintf() output buffer before the length

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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 <david.laight.linux@gmail.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260302101815.3043-5-david.laight.linux@gmail.com
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
This commit is contained in:
David Laight 2026-03-02 10:17:56 +00:00 committed by Thomas Weißschuh
parent b42f02da2b
commit 9aa8a4afd4
1 changed files with 9 additions and 7 deletions
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16
tools/testing/selftests/nolibc/nolibc-test.c
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@ -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)