Re: [PATCH v4] [GSOC]trailer: pass arg as positional parameter

[ZheNing Hu <adlternative@gmail.com>]

Hi, Junio,

ZheNing Hu <adlternative@gmail.com> 于2021年3月30日周二 下午7:22写道：
>
> In addition, I now found a small bug in ".cmd",
>
> git config -l |grep bug
> trailer.bug.key=bug-descibe:
> trailer.bug.ifexists=replace
> trailer.bug.cmd=echo 123
>
> see what will happen:
>
> git interpret-trailers --trailer="bug:text" <<-EOF
> `heredocd> EOF
>
> bug-descibe:123 text
>
> "text" seem print to stdout.
>
> I'm looking at what's going on here.
>

Here I may need to think with you whether it is reasonable to pass "$1".

I found that we passed the parameters in the above situation like this:

(gdb) print cp.args.v[0]
$7 = 0x5555558f4e20 "echo \"123\""
(gdb) print cp.args.v[1]
$8 = 0x5555558ee150 "text"

At this time, our idea is base on that v[0] will be the content of the shell,
and v[1] will be the $1 of the shell.

But in fact, git handles shell subprocesses in a special way:

The `prepare_shell_cmd()` in "run-command.c" seem to use "$@" to pass
shell args.

Before exec:

(gdb) print argv.v[1]
$22 = 0x5555558edfd0 "/bin/sh"
(gdb) print argv.v[2]
$23 = 0x5555558f4c80 "-c"
(gdb) print argv.v[3]
$24 = 0x5555558ed4b0 "echo \"123\" \"$@\""
(gdb) print argv.v[4]
$25 = 0x5555558f5980 "echo \"123\""
(gdb) print argv.v[5]
$26 = 0x5555558edab0 "abc"
(gdb) print argv.v[6]
$27 = 0x0

Some unexpected things happened here.
Maybe "abc" was wrongly used as the parameter of "echo"?
Looking forward to your reply.

--
ZheNing Hu