Test suite failures under UndefinedBehaviorSanitizer (UBSAN)

[Sam James]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: x86_64-pc-linux-gnu-gcc
Compilation CFLAGS: -O2 -pipe -march=native -fdiagnostics-color=always 
-frecord-gcc-switches -Wreturn-type -ggdb3 -DNDEBUG
uname output: Linux mop 5.15.85-gentoo-dist-hardened #1 SMP Thu Dec 22 21:20:03 
GMT 2022 x86_64 AMD Ryzen 9 3950X 16-Core Processor AuthenticAMD GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Gawk Version: 5.2.1

Attestation 1:
        I have read 
https://www.gnu.org/software/gawk/manual/html_node/Bugs.html.

Attestation 2:
        I have not modified the sources before building gawk.

Description:
        When built with UndefinedBehaviorSanitizer (UBSAN), gawk's test suite
        seems to have some errors which indicates the presence of undefined 
behavior.

        I noticed this when looking into a recent bug report on bug-gawk
        about a miscompiled gawk when built with Clang:
        https://lists.gnu.org/archive/html/bug-gawk/2022-12/msg00010.html.

        (It's common for compiler developers to ask if you tested your code
        with sanitizers when reporting a miscompilation.)

Repeat-By:
        1. git clone gawk
        2. ./configure CFLAGS="-O2 -fsanitize=undefined -ggdb3" 
LDFLAGS="-fsanitize=undefined -ggdb3"
        3. make check (and see failure in pipeio2 test)
        4. Run the pipeio2 test by itself to get more details:
```
$ export UBSAN_OPTIONS=print_stacktrace=1
 $ ./gawk -v SRCDIR=/tmp/gawk/test -f test/pipeio2.awk
'echo    January 1997 | sed "s/[0-9]/./g"'
January ....
'echo  S  M Tu  W Th  F  S | sed "s/[0-9]/./g"'
S M Tu W Th F S
'echo           1  2  3  4 | sed "s/[0-9]/./g"'
. . . .
'echo  5  6  7  8  9 10 11 | sed "s/[0-9]/./g"'
. . . . . .. ..
'echo 12 13 14 15 16 17 18 | sed "s/[0-9]/./g"'
.. .. .. .. .. .. ..
'echo 19 20 21 22 23 24 25 | sed "s/[0-9]/./g"'
.. .. .. .. .. .. ..
'echo 26 27 28 29 30 31 | sed "s/[0-9]/./g"'
.. .. .. .. .. ..
node.c:423:3: runtime error: null pointer passed as argument 2, which is 
declared to never be null
    #0 0x41191c in make_str_node /tmp/gawk/node.c:423
    #1 0x550483 in do_getline_redir /tmp/gawk/io.c:2871
    #2 0x4ef1f6 in r_interpret /tmp/gawk/interpret.h:1330
    #3 0x41929e in main /tmp/gawk/main.c:538
    #4 0x7fcfe19e064f in __libc_start_call_main 
../sysdeps/nptl/libc_start_call_main.h:58
    #5 0x7fcfe19e0708 in __libc_start_main_impl ../csu/libc-start.c:381
    #6 0x41af14 in _start ../sysdeps/x86_64/start.S:115
```

Fix:
        I don't think this is necessarily a correct fix, but this
        patch sliences it at least:
```
--- a/io.c
+++ b/io.c
@@ -2844,7 +2844,7 @@ do_getline_redir(int into_variable, enum redirval 
redirtype)

        errcode = 0;
        cnt = get_a_record(& s, iop, & errcode, (lhs ? NULL : & field_width));
-       if (errcode != 0) {
+       if (!cnt || errcode != 0) {
                if (! do_traditional && (errcode != -1))
                        update_ERRNO_int(errcode);
                return make_number((AWKNUM) cnt);
```

        Feel free to ignore the patch if it doesn't look right. I won't be 
offended ;)

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