Add support for dealing with string operands, including reading a string
from memory into an environment variable and concatenating two strings.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Marek Behún <marek.behun@nic.cz>

At present when more than one substitution is made this function
overwrites its buffers. Fix this bug and update the tests now that they
can pass.

Also update the debug code to show all substrings, since at present it
omits the final one.

Fixes: 855f18ea0e6 ("setexpr: add regex substring matching and substitution")
Signed-off-by: Simon Glass <sjg@chromium.org>

At present the 'nlen' variable increases with each loop. If the previous
loop had back references, then subsequent loops without back references
use the wrong value of nlen. The value is larger, meaning that the string
terminator from nbuf is copied along to the main buffer, thus terminating
the string prematurely.

This leads to the final result being truncated, e.g. missing the last
(unmatched) part of the string. So "match match tail" become
"replaced replaced" instead of "replaced replaced tail".

Fix this by resetting nlen to the correct value each time around the lop.

Fixes: 855f18ea0e6 ("setexpr: add regex substring matching and substitution")
Signed-off-by: Simon Glass <sjg@chromium.org>

Add tests to check for buffer overflow using simple replacement as well
as back references. At present these don't fully pass.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add tests for the setexpr regex commands.

Note that these tests currently crash on sandbox due to an existing bug in
the setexpr implementation, so two of the tests are commented out.

Signed-off-by: Simon Glass <sjg@chromium.org>

At present this function assumes that a size of 4 refers to a ulong. This
is true on 32-bit machines but not commonly on 64-bit machines.

This means that the 'l' specify does not work correctly with setexpr.

Add an explicit case for 32-bit values so that 64-bit machines can still
use the 'l' specifier. On 32-bit machines, 64-bit is still not supported.

This corrects the operation of the default size (which is 4 for setexpr),
so update the tests accordingly.

The original code for reading from memory was included in 47ab5ad1457
("cmd_setexpr: allow memory addresses in expressions") but I am not adding
a Fixes: tag since that code was not written with 64-bit machines in mind.

Signed-off-by: Simon Glass <sjg@chromium.org>

This command currently has no tests. Add some for basic assignment and the
integer operations.

Note that the default size for setexpr is ulong, which varies depending on
the build machine. So for sandbox on a 64-bit host, this means that the
default size is 64 bits.

Signed-off-by: Simon Glass <sjg@chromium.org>