Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756966Ab3JKHKg (ORCPT ); Fri, 11 Oct 2013 03:10:36 -0400 Received: from mail4.hitachi.co.jp ([133.145.228.5]:57611 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756558Ab3JKHK2 (ORCPT ); Fri, 11 Oct 2013 03:10:28 -0400 Subject: [PATCH -tip 2/2] perf probe: Find fentry mcount fuzzed parameter location To: Arnaldo Carvalho de Melo From: Masami Hiramatsu Cc: Ingo Molnar , Paul Mackerras , lkml , Peter Zijlstra Date: Fri, 11 Oct 2013 16:10:26 +0900 Message-ID: <20131011071025.15557.13275.stgit@udc4-manage.rcp.hitachi.co.jp> In-Reply-To: <20131011071020.15557.20050.stgit@udc4-manage.rcp.hitachi.co.jp> References: <20131011071020.15557.20050.stgit@udc4-manage.rcp.hitachi.co.jp> User-Agent: StGit/0.15 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4910 Lines: 135 At this point, --fentry (mcount founction entry) option for gcc fuzzes the debuginfo variable locations by skipping the mcount instruction offset (on x86, this is a 5 byte call instruction). This makes variable searching failure at the entry of functions which are mcount'ed. e.g.) # perf probe --vars vfs_read Available variables at vfs_read @ (No matched variables) This patch adds additional location search at the function entry point to solve this issue, which tries to find the earliest address for the variable location. Note that this is only works with function parameters (formal parameters) because any local variables should not exist on the function entry address (those are not initialized yet). With this patch, perf probe shows correct parameters if possible; # perf probe --vars vfs_read Available variables at vfs_read @ char* buf loff_t* pos size_t count struct file* file Signed-off-by: Masami Hiramatsu Cc: Peter Zijlstra Cc: Paul Mackerras Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo --- tools/perf/util/probe-finder.c | 39 +++++++++++++++++++++++++++++++-------- 1 file changed, 31 insertions(+), 8 deletions(-) diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c index 5a46be9..c044052 100644 --- a/tools/perf/util/probe-finder.c +++ b/tools/perf/util/probe-finder.c @@ -273,12 +273,15 @@ static struct probe_trace_arg_ref *alloc_trace_arg_ref(long offs) /* * Convert a location into trace_arg. * If tvar == NULL, this just checks variable can be converted. + * If fentry == true and vr_die is a parameter, do huristic search + * for the location fuzzed by function entry mcount. */ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, - Dwarf_Op *fb_ops, + Dwarf_Op *fb_ops, Dwarf_Die *sp_die, struct probe_trace_arg *tvar) { Dwarf_Attribute attr; + Dwarf_Addr tmp = 0; Dwarf_Op *op; size_t nops; unsigned int regn; @@ -291,12 +294,29 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr, goto static_var; /* TODO: handle more than 1 exprs */ - if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL || - dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0 || - nops == 0) { - /* TODO: Support const_value */ + if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL) + return -EINVAL; /* Broken DIE ? */ + if (dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0) { + ret = dwarf_entrypc(sp_die, &tmp); + if (ret || addr != tmp || + dwarf_tag(vr_die) != DW_TAG_formal_parameter || + dwarf_highpc(sp_die, &tmp)) + return -ENOENT; + /* + * This is fuzzed by fentry mcount. We try to find the + * parameter location at the earliest address. + */ + for (addr += 1; addr <= tmp; addr++) { + if (dwarf_getlocation_addr(&attr, addr, &op, + &nops, 1) > 0) + goto found; + } return -ENOENT; } +found: + if (nops == 0) + /* TODO: Support const_value */ + return -ENOENT; if (op->atom == DW_OP_addr) { static_var: @@ -600,7 +620,7 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf) dwarf_diename(vr_die)); ret = convert_variable_location(vr_die, pf->addr, pf->fb_ops, - pf->tvar); + &pf->sp_die, pf->tvar); if (ret == -ENOENT) pr_err("Failed to find the location of %s at this address.\n" " Perhaps, it has been optimized out.\n", pf->pvar->var); @@ -1148,13 +1168,15 @@ struct local_vars_finder { static int copy_variables_cb(Dwarf_Die *die_mem, void *data) { struct local_vars_finder *vf = data; + struct probe_finder *pf = vf->pf; int tag; tag = dwarf_tag(die_mem); if (tag == DW_TAG_formal_parameter || tag == DW_TAG_variable) { if (convert_variable_location(die_mem, vf->pf->addr, - vf->pf->fb_ops, NULL) == 0) { + vf->pf->fb_ops, &pf->sp_die, + NULL) == 0) { vf->args[vf->nargs].var = (char *)dwarf_diename(die_mem); if (vf->args[vf->nargs].var == NULL) { vf->ret = -ENOMEM; @@ -1302,7 +1324,8 @@ static int collect_variables_cb(Dwarf_Die *die_mem, void *data) if (tag == DW_TAG_formal_parameter || tag == DW_TAG_variable) { ret = convert_variable_location(die_mem, af->pf.addr, - af->pf.fb_ops, NULL); + af->pf.fb_ops, &af->pf.sp_die, + NULL); if (ret == 0) { ret = die_get_varname(die_mem, buf, MAX_VAR_LEN); pr_debug2("Add new var: %s\n", buf); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/