[PATCH 2 of 2 V3] osutil: implement setprocname to set process title for some platforms

[Yuya Nishihara]

On Sun, 13 Nov 2016 15:25:46 +0000, Jun Wu wrote:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1478898677 0
> #      Fri Nov 11 21:11:17 2016 +0000
> # Node ID c4af4fec293bed4e5105442137a24c34d58e740f
> # Parent  98761d64eaaf67f3bdb99f3f80a57910e2624b78
> # Available At https://bitbucket.org/quark-zju/hg-draft
> #              hg pull https://bitbucket.org/quark-zju/hg-draft -r c4af4fec293b
> osutil: implement setprocname to set process title for some platforms

> +#ifndef SETPROCNAME_USE_NONE
> +static PyObject *setprocname(PyObject *self, PyObject *args)
> +{
> +	const char *name = NULL;
> +	if (!PyArg_ParseTuple(args, "s", &name))
> +		return NULL;
> +
> +#if defined(SETPROCNAME_USE_SETPROCTITLE)
> +	setproctitle("%s", name);
> +#elif defined(SETPROCNAME_USE_ARGVREWRITE)
> +	{
> +		static char *argvstart = NULL;
> +		static size_t argvsize = 0;
> +		if (argvstart == NULL) {
> +			int argc = 0, i;
> +			char **argv = NULL;
> +			extern void Py_GetArgcArgv(int *argc, char ***argv);
> +			Py_GetArgcArgv(&argc, &argv);
> +
> +			/* Check the memory we can use. Typically, argv[i] and
> +			 * argv[i + 1] are continuous. */
> +			for (argvstart = argv[0], i = 0; i < argc; ++i) {
> +				if (argv[i] > argvstart + argvsize)
> +					break; /* not continuous */
> +				size_t len = strlen(argv[i]);
> +				argvsize = argv[i] - argv[0] + len + 1;
> +			}

Segfaults if argv[i] < argv[0].

  % gdb python
  (gdb) run -c 'from mercurial import osutil; osutil.setprocname("foo")'
  (gdb) p argc
  $25 = 3
  (gdb) p argv[0]
  $28 = 0x7fffffffe307 "/usr/bin/python"
  (gdb) p argv[1]
  $29 = 0x7fffffffe317 "-c"
  (gdb) p argv[2]
  $30 = 0x555555763dd8 "-c"

I think the original "argv[i] == argvstart + argvsize" was simple enough. We
can't calculate the exact capacity of underlying buffer anyway once it's
clobbered (and zero-filled.)

> +		if (argvstart && argvsize > 1) {
> +			int n = snprintf(argvstart, argvsize, "%s", name);
> +			if (n >= 0 && (size_t)n < argvsize)
> +				memset(argvstart + n, 0, argvsize - n);
> +		}
> +	}