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From: "jiangchuanganghw at outlook dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/112783] core dump on libxo when function is inlined
Date: Fri, 05 Jan 2024 03:09:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112783

Jiang ChuanGang <jiangchuanganghw at outlook dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jiangchuanganghw at outloo=
k dot co
                   |                            |m

--- Comment #9 from Jiang ChuanGang <jiangchuanganghw at outlook dot com> -=
--
(In reply to Andrew Pinski from comment #3)
> The problem is not in GCC but rather a bad assumption on the code part.
>=20
> Basically we have:
>=20
> memcpy(nbuf, name, nlen);
> ...
>=20
>=20
> if (!name)
> ...
>=20
>=20
> But the check after a memcpy can be removed as passing a null pointer to
> memcpy is undefined even if nlen is 0 here.
>=20
>=20
> This patch to the sources fixes the issue for me:
> ```
> diff --git a/libxo/libxo.c b/libxo/libxo.c
> index 916a111..ea71723 100644
> --- a/libxo/libxo.c
> +++ b/libxo/libxo.c
> @@ -4300,7 +4300,8 @@ xo_format_value (xo_handle_t *xop, const char *name,
> ssize_t nlen,
>         if ((xsp->xs_flags & (XSF_EMIT | XSF_EMIT_KEY))
>             || !(xsp->xs_flags & XSF_EMIT_LEAF_LIST)) {
>             char nbuf[nlen + 1];
> -           memcpy(nbuf, name, nlen);
> +            if (name)
> +             memcpy(nbuf, name, nlen);
>             nbuf[nlen] =3D '\0';
>=20
>             ssize_t rc =3D xo_transition(xop, 0, nbuf, XSS_EMIT_LEAF_LIST=
);
> @@ -4324,7 +4325,8 @@ xo_format_value (xo_handle_t *xop, const char *name,
> ssize_t nlen,
>=20
>         } else if (!(xsp->xs_flags & XSF_EMIT_KEY)) {
>             char nbuf[nlen + 1];
> -           memcpy(nbuf, name, nlen);
> +            if (name)
> +             memcpy(nbuf, name, nlen);
>             nbuf[nlen] =3D '\0';
>=20
>             ssize_t rc =3D xo_transition(xop, 0, nbuf, XSS_EMIT);
> @@ -4342,7 +4344,8 @@ xo_format_value (xo_handle_t *xop, const char *name,
> ssize_t nlen,
>         if ((xsp->xs_flags & XSF_EMIT_LEAF_LIST)
>             || !(xsp->xs_flags & XSF_EMIT)) {
>             char nbuf[nlen + 1];
> -           memcpy(nbuf, name, nlen);
> +            if (name)
> +             memcpy(nbuf, name, nlen);
>             nbuf[nlen] =3D '\0';
>=20
>             ssize_t rc =3D xo_transition(xop, 0, nbuf, XSS_EMIT);
>=20
> ```

I've encountered the same bug, and your solution does fix it.
But strangely enough, I can't reproduce it with code like the following.
The inevitable condition of this bug still puzzles me. Do you have any thou=
ghts
on this.


#include <stdio.h>
#include <string.h>

static const char *xo_xml_leader_len(const char *name, int len)
{
    if (name =3D=3D NULL || name[0] =3D=3D '_')
            return "";
        return "_";
}

void test()
{
    char *name =3D NULL;
        int len =3D 0;
        char mbuf[len + 1];
        memcpy(mbuf, name, len);
        mbuf[len] =3D '\0';
        const char *leader =3D xo_xml_leader_len(name, len);
        printf("leader: %s", leader);
}

int main()
{
    test();
        return 0;
}=