netdev - Re: [PATCH bpf-next] bpftool: Remove usage of reallocarray()

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Message-ID: <0958851a-2ff7-d51c-0e90-1c3e04207529@iogearbox.net>
Date:   Sat, 19 Feb 2022 00:30:38 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Mauricio Vásquez <mauricio@...volk.io>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>
Subject: Re: [PATCH bpf-next] bpftool: Remove usage of reallocarray()

On 2/18/22 9:39 PM, Mauricio Vásquez wrote:
> This commit fixes a compilation error on systems with glibc < 2.26 [0]:
> 
> ```
> In file included from main.h:14:0,
>                   from gen.c:24:
> linux/tools/include/tools/libc_compat.h:11:21: error: attempt to use poisoned "reallocarray"
>   static inline void *reallocarray(void *ptr, size_t nmemb, size_t size)
> ```
> 
> This happens because gen.c pulls <bpf/libbpf_internal.h>, and then
> <tools/libc_compat.h> (through main.h). When
> COMPAT_NEED_REALLOCARRAY is set, libc_compat.h defines reallocarray()
> which libbpf_internal.h poisons with a GCC pragma.
> 
> This follows the same approach of libbpf in commit
> 029258d7b228 ("libbpf: Remove any use of reallocarray() in libbpf").
> 
> Reported-by: Quentin Monnet <quentin@...valent.com>
> Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> 
> [0]: https://lore.kernel.org/bpf/3bf2bd49-9f2d-a2df-5536-bc0dde70a83b@isovalent.com/
[...]
> + * Copied from tools/lib/bpf/libbpf_internal.h
> + */
> +static inline void *bpftool_reallocarray(void *ptr, size_t nmemb, size_t size)
> +{
> +	size_t total;
> +
> +#if __has_builtin(__builtin_mul_overflow)
> +	if (unlikely(__builtin_mul_overflow(nmemb, size, &total)))
> +		return NULL;
> +#else
> +	if (size == 0 || nmemb > ULONG_MAX / size)
> +		return NULL;
> +	total = nmemb * size;
> +#endif
> +	return realloc(ptr, total);
> +}

Can't we just reuse libbpf_reallocarray() given we copy over libbpf_internal.h
anyway via a9caaba399f9 ("bpftool: Implement "gen min_core_btf" logic")?

Thanks,
Daniel