view auto/endianness @ 6627:ad736705a744

HTTP/2: avoid left-shifting signed integer into the sign bit. On non-aligned platforms, properly cast argument before left-shifting it in ngx_http_v2_parse_uint32 that is used with u_char. Otherwise it propagates to int to hold the value and can step over the sign bit. Usually, on known compilers, this results in negation. Furthermore, a subsequent store into a wider type, that is ngx_uint_t on 64-bit platforms, results in sign-extension. In practice, this can be observed in debug log as a very large exclusive bit value, when client sent PRIORITY frame with exclusive bit set: : *14 http2 PRIORITY frame sid:5 on 1 excl:8589934591 weight:17 Found with UndefinedBehaviorSanitizer.
author Sergey Kandaurov <pluknet@nginx.com>
date Thu, 07 Jul 2016 21:03:21 +0300
parents e3faa5fb7772
children
line wrap: on
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# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


echo $ngx_n "checking for system byte ordering ...$ngx_c"

cat << END >> $NGX_AUTOCONF_ERR

----------------------------------------
checking for system byte ordering

END


cat << END > $NGX_AUTOTEST.c

int main(void) {
    int i = 0x11223344;
    char *p;

    p = (char *) &i;
    if (*p == 0x44) return 0;
    return 1;
}

END

ngx_test="$CC $CC_TEST_FLAGS $CC_AUX_FLAGS \
          -o $NGX_AUTOTEST $NGX_AUTOTEST.c $NGX_LD_OPT $ngx_feature_libs"

eval "$ngx_test >> $NGX_AUTOCONF_ERR 2>&1"

if [ -x $NGX_AUTOTEST ]; then
    if $NGX_AUTOTEST >/dev/null 2>&1; then
        echo " little endian"
        have=NGX_HAVE_LITTLE_ENDIAN . auto/have
    else
        echo " big endian"
    fi

    rm -rf $NGX_AUTOTEST*

else
    rm -rf $NGX_AUTOTEST*

    echo
    echo "$0: error: cannot detect system byte ordering"
    exit 1
fi