On Mon, Sep 28, 2020 at 02:39:42PM +0200, Ahmad Fatoum wrote:
> Instead of storing pointers to 4-byte strings, we could just store the
> characters directly in the struct. Can save us up to 18 pointers worth
> of space.
>
> We could save 18 x 1 byte more of static storage by making the strings
> 3 bytes of length as the nul byte need not be stored explicitly for
> strings of maximal length.
>
> For clarity, this optimization is omitted for now. We still use strncmp,
> instead of strcmp use runs risk of accidental out of bounds reads when
> longer escape sequences are added. This can't occur with strncmp.
>
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> v1 -> v2:
> - Maintain a nul delimiter always at the cost of 18 more bytes
> (Sascha)
> ---
> lib/readkey.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/lib/readkey.c b/lib/readkey.c
> index c26e9d51aba9..6a4ddf14a99d 100644
> --- a/lib/readkey.c
> +++ b/lib/readkey.c
> @@ -20,8 +20,10 @@
> #include <linux/ctype.h>
> #include <readkey.h>
>
> +#define MAX_ESC_LEN 4
> +
> struct esc_cmds {
> - const char *seq;
> + const char seq[MAX_ESC_LEN];
> unsigned char val;
> };
>
> @@ -49,7 +51,7 @@ static const struct esc_cmds esccmds[] = {
> int read_key(void)
> {
> unsigned char c;
> - unsigned char esc[5];
> + unsigned char esc[MAX_ESC_LEN + 2];
> c = getchar();
>
> if (c == 27) {
> @@ -67,7 +69,7 @@ int read_key(void)
> }
> esc[i] = 0;
> for (i = 0; i < ARRAY_SIZE(esccmds); i++){
> - if (!strcmp(esc, esccmds[i].seq))
> + if (!strncmp(esc, esccmds[i].seq, MAX_ESC_LEN))
> return esccmds[i].val;
strncmp() gives you undesired results when 'esc' is longer than
MAX_ESC_LEN. Please don't start proving me that this can't happen in the
current code. I still don't think that saving a few bytes is worth the
hassle.
Sascha
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