tree 79623a9926f3e3ac979029d66b30f22f8c488fdc
parent 6cda0b04a3d3c36312adf7a9aa608306f6a5704a
author Denys Vlasenko <vda.linux@googlemail.com> 1582534970 +0100
committer Denys Vlasenko <vda.linux@googlemail.com> 1582568451 +0100

ash: expand: Do not reprocess data when expanding words

Upstream patch:

    Date: Wed, 30 May 2018 02:06:03 +0800
    expand: Do not reprocess data when expanding words

    Currently various paths will reprocess data when performing word
    expansion.  For example, expari will skip backwards looking for
    the start of the arithmetic expansion, while evalvar will skip
    unexpanded words manually.

    This is cumbersome and error-prone.  This patch fixes this by
    making word expansions proceed in a linear fashion.  This means
    changing argstr and the various expansion functions such as expari
    and subevalvar to return the next character to be expanded.

    This is inspired by similar code from FreeBSD.  However, we take
    things one step further and completely remove the manual word
    skipping in evalvar.  This is accomplished by introducing a new
    EXP_DISCARD flag that tells argstr to only parse and not produce
    any actual expansions.

    Incidentally, argstr will now always NUL-terminate the expansion
    unless the EXP_WORD flag is set.  This is because all but one
    caller of argstr wants the result to be NUL-termianted.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Also includes two one-line follow-up fixes:

    expand: Eat closing brace for length parameter
            if (subtype == VSLENGTH) {
    +               p++;
                    if (flag & EXP_DISCARD)
    expand: Fix double-decrement in argstr
    -               newloc = expdest - (char *)stackblock() - end;
    +               newloc = q - (char *)stackblock() - end;

and changes in code for bash substring extensions.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>