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Wed, 12 Feb 2025 13:20:11 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1FF1120043; Wed, 12 Feb 2025 13:20:11 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 661022004E; Wed, 12 Feb 2025 13:20:05 +0000 (GMT) Received: from localhost.localdomain (unknown [9.61.242.147]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Feb 2025 13:20:04 +0000 (GMT) From: Athira Rajeev To: acme@kernel.org, jolsa@kernel.org, adrian.hunter@intel.com, irogers@google.com, namhyung@kernel.org Cc: linux-perf-users@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, maddy@linux.ibm.com, atrajeev@linux.vnet.ibm.com, kjain@linux.ibm.com, disgoel@linux.vnet.ibm.com, hbathini@linux.vnet.ibm.com, Aditya.Bodkhe1@ibm.com Subject: [PATCH] tools/perf: Pick the correct dwarf die while adding probe point for a function Date: Wed, 12 Feb 2025 18:49:49 +0530 Message-Id: <20250212131949.68706-1-atrajeev@linux.vnet.ibm.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: _dI9D5PWgel5RddFmlqmlM7J0fVqbajF X-Proofpoint-GUID: eXtSnEdc3-1pRlacr0PHySAuZKlAZuzy X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-12_04,2025-02-11_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 impostorscore=0 mlxscore=0 adultscore=0 mlxlogscore=999 priorityscore=1501 bulkscore=0 lowpriorityscore=0 suspectscore=0 spamscore=0 phishscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2501170000 definitions=main-2502120101 Perf probe on vfs_fstatat fails as below on a powerpc system ./perf probe -nf --max-probes=512 -a 'vfs_fstatat $params' Segmentation fault (core dumped) This is observed while running perftool-testsuite_probe testcase. While running with verbose, its observed that segfault happens at: synthesize_probe_trace_arg () synthesize_probe_trace_command () probe_file.add_event () apply_perf_probe_events () __cmd_probe () cmd_probe () run_builtin () handle_internal_command () main () Code in synthesize_probe_trace_arg() access a null value and results in segfault. Data structure which is null: struct probe_trace_arg arg->value We are hitting a case where arg->value is null in probe point: "vfs_fstatat $params". This is happening since 'commit e896474fe485 ("getname_maybe_null() - the third variant of pathname copy-in")' Before the commit, probe point for vfs_fstatat was getting added only for one location: Writing event: p:probe/vfs_fstatat _text+6345404 dfd=%gpr3:s32 filename=%gpr4:x64 stat=%gpr5:x64 flags=%gpr6:s32 With this change, vfs_fstatat code is inlined for other locations in the code: Probe point found: __do_sys_lstat64+48 Probe point found: __do_sys_stat64+48 Probe point found: __do_sys_newlstat+48 Probe point found: __do_sys_newstat+48 Probe point found: vfs_fstatat+0 When trying to find matching dwarf information entry (DIE) from the debuginfo, the code incorrectly picks DIE which is not referring to vfs_fstatat. Snippet from dwarf entry in vmlinux debuginfo file. The main abstract die is: <1><4214883>: Abbrev Number: 147 (DW_TAG_subprogram) <4214885> DW_AT_external : 1 <4214885> DW_AT_name : (indirect string, offset: 0x17b9f3): vfs_fstatat With formal parameters: <2><4214896>: Abbrev Number: 51 (DW_TAG_formal_parameter) <4214897> DW_AT_name : dfd <2><42148a3>: Abbrev Number: 23 (DW_TAG_formal_parameter) <42148a4> DW_AT_name : (indirect string, offset: 0x8fda9): filename <2><42148b0>: Abbrev Number: 23 (DW_TAG_formal_parameter) <42148b1> DW_AT_name : (indirect string, offset: 0x16bd9c): stat <2><42148bd>: Abbrev Number: 23 (DW_TAG_formal_parameter) <42148be> DW_AT_name : (indirect string, offset: 0x39832b): flags While collecting variables/parameters for a probe point, the function copy_variables_cb() also looks at dwarf debug entries based on the instruction address. Snippet if (dwarf_haspc(die_mem, vf->pf->addr)) return DIE_FIND_CB_CONTINUE; else return DIE_FIND_CB_SIBLING; But incase of inlined function instance for vfs_fstatat, there are two entries which has the instruction address entry point as same. Instance 1: which is for vfs_fstatat and DW_AT_abstract_origin points to 0x4214883 (reference above for main abstract die) <3><42131fa>: Abbrev Number: 59 (DW_TAG_inlined_subroutine) <42131fb> DW_AT_abstract_origin: <0x4214883> <42131ff> DW_AT_entry_pc : 0xc00000000062b1e0 Instance 2: which is not for vfs_fstatat but for getname <5><4213270>: Abbrev Number: 39 (DW_TAG_inlined_subroutine) <4213271> DW_AT_abstract_origin: <0x4215b6b> <4213275> DW_AT_entry_pc : 0xc00000000062b1e0 But the copy_variables_cb() continues to add parameters from second instance also based on the dwarf_haspc() check. This results in formal parameters for getname also appended to params. But while filling in the args->value for these parameters, since these args are not part of dwarf with offset "42131fa". Hence value will be null. This incorrect args results in segfault when value field is accessed. Save the Dwarf_Die which is the actual DW_TAG_subprogram as part of "struct probe_finder". In copy_variables_cb(), include check to make sure the DW_AT_abstract_origin points to the correct entry if the dwarf_haspc() matches the instruction address. Signed-off-by: Athira Rajeev --- tools/perf/util/probe-finder.c | 21 ++++++++++++++++++--- tools/perf/util/probe-finder.h | 1 + 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c index 1e769b68da37..361086a7adae 100644 --- a/tools/perf/util/probe-finder.c +++ b/tools/perf/util/probe-finder.c @@ -973,6 +973,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data) pr_debug("Matched function: %s [%lx]\n", dwarf_diename(sp_die), (unsigned long)dwarf_dieoffset(sp_die)); pf->fname = fname; + memcpy(&pf->abstract_die, sp_die, sizeof(Dwarf_Die)); if (pp->line) { /* Function relative line */ dwarf_decl_line(sp_die, &pf->lno); pf->lno += pp->line; @@ -1179,6 +1180,8 @@ 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; + Dwarf_Attribute attr; + Dwarf_Die var_die; tag = dwarf_tag(die_mem); if (tag == DW_TAG_formal_parameter || @@ -1196,10 +1199,22 @@ static int copy_variables_cb(Dwarf_Die *die_mem, void *data) } } - if (dwarf_haspc(die_mem, vf->pf->addr)) + if (dwarf_haspc(die_mem, vf->pf->addr)) { + /* + * when DW_AT_entry_pc contains instruction address, + * also check if the DW_AT_abstract_origin of die_mem + * points to correct die. + */ + if (dwarf_attr(die_mem, DW_AT_abstract_origin, &attr)) { + dwarf_formref_die(&attr, &var_die); + if (dwarf_dieoffset(&pf->abstract_die) != dwarf_dieoffset(&var_die)) + goto out; + } return DIE_FIND_CB_CONTINUE; - else - return DIE_FIND_CB_SIBLING; + } + +out: + return DIE_FIND_CB_SIBLING; } static int expand_probe_args(Dwarf_Die *sc_die, struct probe_finder *pf, diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h index dcf6cc1e1cbe..b3039635c94e 100644 --- a/tools/perf/util/probe-finder.h +++ b/tools/perf/util/probe-finder.h @@ -63,6 +63,7 @@ struct probe_finder { const char *fname; /* Real file name */ Dwarf_Die cu_die; /* Current CU */ Dwarf_Die sp_die; + Dwarf_Die abstract_die; struct intlist *lcache; /* Line cache for lazy match */ /* For variable searching */ -- 2.43.5