Date: Mon, 16 Sep 2013 13:19:57 -0500 From: Nico Williams <nico@cryptonector.com> To: Mark Johnston <markj@freebsd.org> Cc: dtrace-discuss@lists.dtrace.org, freebsd-dtrace@freebsd.org Subject: Re: [dtrace-discuss] pr_psargs on FreeBSD Message-ID: <CAK3OfOg_0paqdQpAjt4u0ZPfaV8eRQ5pWNf-9TADGT6g8PPNXQ@mail.gmail.com> In-Reply-To: <20130915221622.GA2981@raichu> References: <20130915221622.GA2981@raichu>
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On Sun, Sep 15, 2013 at 5:16 PM, Mark Johnston <markj@freebsd.org> wrote:
> Hi!
>
> One of the problems with FreeBSD's DTrace implementation is that it
> doesn't have a good way of getting the arguments of a given process.
> This is because of the way that they're stored, which is as a single
> buffer with null-terminator between consecutive arguments. In
> particular, there is no way within DTrace to convert such a buffer to a
> single string (say by replacing all but the last terminator with
> spaces). So scripts like execsnoop will only print the first element of
> a process' argv on FreeBSD, which isn't particularly helpful for
> interpreted programs.
>
> You can get a fixed number of arguments with something like
>
> printf("%s %s %s", cupsinfo->pr_psargs,
> curpsinfo->pr_psargs + strlen(curpsinfo->pr_psargs) + 1,
> curpsinfo->pr_psargs + strlen(curpsinfo->pr_psargs) + 1 +
> strlen(curpsinfo->pr_psargs + strlen(curpsinfo->pr_psargs) + 1) + 1);
>
> but this is less than ideal. :)
>
> Apparently OS X has the same problem, but I don't have a machine to test
> with, so I'm not completely sure.
>
> It seems to me that there are two ways to solve this problem: change the
> format that FreeBSD uses to store process arguments, or add a function
> to DTrace which can convert the argument buffer to a string. I'm not too
> keen on the former approach, so here's a proposal for the latter. It'd
> be great to get some feedback on it and find out whether anyone thinks
> it's a terrible idea. :)
>
> It's kind of a strong-armed approach, but the problem's been around for a
> while and I can't think of any clever solutions - I'd love to see an
> alternative solution.
>
> My patch against FreeBSD (pasted below) adds a function called memstr()
> to DTrace. memstr() takes three arguments: addr, c, and len, and returns
> a copy of addr of length len with all null-terminators replaced by c,
> and with the last byte replaced by a null-terminator. In particular,
> memstr() always returns a string of length len - 1, unless len == 0, in
> which case we return the empty string.
>
> With this function, the translator for the pr_psargs fields becomes
>
> translator psinfo_t < struct proc *T > {
> ...
> pr_psargs = memstr(T->p_args->ar_args, ' ', T->p_args->ar_length);
> ...
> };
>
> and execsnoop works properly. Any thoughts on this function? Have I missed
> a better solution? A patch for FreeBSD is below.
>
> Thanks,
> -Mark
>
> diff --git a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c
> index 9c9b2a6..83c81e5 100644
> --- a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c
> +++ b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_open.c
> @@ -122,8 +122,9 @@
> #define DT_VERS_1_8_1 DT_VERSION_NUMBER(1, 8, 1)
> #define DT_VERS_1_9 DT_VERSION_NUMBER(1, 9, 0)
> #define DT_VERS_1_9_1 DT_VERSION_NUMBER(1, 9, 1)
> -#define DT_VERS_LATEST DT_VERS_1_9_1
> -#define DT_VERS_STRING "Sun D 1.9.1"
> +#define DT_VERS_1_9_2 DT_VERSION_NUMBER(1, 9, 2)
> +#define DT_VERS_LATEST DT_VERS_1_9_2
> +#define DT_VERS_STRING "Sun D 1.9.2"
>
> const dt_version_t _dtrace_versions[] = {
> DT_VERS_1_0, /* D API 1.0.0 (PSARC 2001/466) Solaris 10 FCS */
> @@ -145,6 +146,7 @@ const dt_version_t _dtrace_versions[] = {
> DT_VERS_1_8_1, /* D API 1.8.1 */
> DT_VERS_1_9, /* D API 1.9 */
> DT_VERS_1_9_1, /* D API 1.9.1 */
> + DT_VERS_1_9_2, /* D API 1.9.2 */
> 0
> };
>
> @@ -311,6 +313,8 @@ static const dt_ident_t _dtrace_globals[] = {
> &dt_idops_func, "void(@)" },
> { "memref", DT_IDENT_FUNC, 0, DIF_SUBR_MEMREF, DT_ATTR_STABCMN, DT_VERS_1_1,
> &dt_idops_func, "uintptr_t *(void *, size_t)" },
> +{ "memstr", DT_IDENT_FUNC, 0, DIF_SUBR_MEMSTR, DT_ATTR_STABCMN, DT_VERS_1_0,
> + &dt_idops_func, "string(void *, char, size_t)" },
> { "min", DT_IDENT_AGGFUNC, 0, DTRACEAGG_MIN, DT_ATTR_STABCMN, DT_VERS_1_0,
> &dt_idops_func, "void(@)" },
> { "mod", DT_IDENT_ACTFUNC, 0, DT_ACT_MOD, DT_ATTR_STABCMN,
> diff --git a/cddl/lib/libdtrace/psinfo.d b/cddl/lib/libdtrace/psinfo.d
> index 068e72e..b2a009a 100644
> --- a/cddl/lib/libdtrace/psinfo.d
> +++ b/cddl/lib/libdtrace/psinfo.d
> @@ -57,7 +57,7 @@ translator psinfo_t < struct proc *T > {
> pr_gid = T->p_ucred->cr_rgid;
> pr_egid = T->p_ucred->cr_groups[0];
> pr_addr = 0;
> - pr_psargs = stringof(T->p_args->ar_args);
> + pr_psargs = memstr(T->p_args->ar_args, ' ', T->p_args->ar_length);
> pr_arglen = T->p_args->ar_length;
> pr_jailid = T->p_ucred->cr_prison->pr_id;
> };
> diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> index babc42c4..6d991fb 100644
> --- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> +++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
> @@ -4920,6 +4920,38 @@ inetout: regs[rd] = (uintptr_t)end + 1;
> break;
> }
>
> + case DIF_SUBR_MEMSTR: {
> + char *str = (char *)mstate->dtms_scratch_ptr;
> + uintptr_t mem = tupregs[0].dttk_value;
> + char c = tupregs[1].dttk_value;
> + size_t size = tupregs[2].dttk_value;
> + uint8_t n;
> + int i;
> +
> + regs[rd] = 0;
> +
> + if (size == 0)
> + break;
> +
> + if (!dtrace_canload(mem, size - 1, mstate, vstate))
> + break;
> +
> + if (!DTRACE_INSCRATCH(mstate, size)) {
> + DTRACE_CPUFLAG_SET(CPU_DTRACE_NOSCRATCH);
> + break;
> + }
> +
> + for (i = 0; i < size - 1; i++) {
> + n = dtrace_load8(mem++);
> + str[i] = (n == 0) ? c : n;
> + }
> + str[size - 1] = 0;
> +
> + regs[rd] = (uintptr_t)str;
> + mstate->dtms_scratch_ptr += size;
> + break;
> + }
> +
> case DIF_SUBR_TYPEREF: {
> uintptr_t size = 4 * sizeof(uintptr_t);
> uintptr_t *typeref = (uintptr_t *) P2ROUNDUP(mstate->dtms_scratch_ptr, sizeof(uintptr_t));
> @@ -9102,6 +9134,7 @@ dtrace_difo_validate_helper(dtrace_difo_t *dp)
> subr == DIF_SUBR_NTOHL ||
> subr == DIF_SUBR_NTOHLL ||
> subr == DIF_SUBR_MEMREF ||
> + subr == DIF_SUBR_MEMSTR ||
> subr == DIF_SUBR_TYPEREF)
> break;
>
> diff --git a/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h b/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
> index 8728e30..295457c 100644
> --- a/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
> +++ b/sys/cddl/contrib/opensolaris/uts/common/sys/dtrace.h
> @@ -311,8 +311,9 @@ typedef enum dtrace_probespec {
> #define DIF_SUBR_SX_SHARED_HELD 48
> #define DIF_SUBR_SX_EXCLUSIVE_HELD 49
> #define DIF_SUBR_SX_ISEXCLUSIVE 50
> +#define DIF_SUBR_MEMSTR 51
>
> -#define DIF_SUBR_MAX 50 /* max subroutine value */
> +#define DIF_SUBR_MAX 51 /* max subroutine value */
>
> typedef uint32_t dif_instr_t;
>
>
>
> -------------------------------------------
> dtrace-discuss
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