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Fri, 15 Nov 2024 11:36:13 GMT Received: from pps.reinject (localhost [127.0.0.1]) by phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 42sx6c38bh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Nov 2024 11:36:12 +0000 Received: from phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 4AFBa9PH010008; Fri, 15 Nov 2024 11:36:12 GMT Received: from bpf.uk.oracle.com (dhcp-10-175-214-128.vpn.oracle.com [10.175.214.128]) by phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTP id 42sx6c388q-2; Fri, 15 Nov 2024 11:36:12 +0000 From: Alan Maguire To: acme@kernel.org Cc: yonghong.song@linux.dev, dwarves@vger.kernel.org, ast@kernel.org, andrii@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, kernel-team@fb.com, song@kernel.org, eddyz87@gmail.com, olsajiri@gmail.com, Alan Maguire Subject: [PATCH v3 dwarves 1/2] dwarf_loader: Check DW_OP_[GNU_]entry_value for possible parameter matching Date: Fri, 15 Nov 2024 11:36:04 +0000 Message-ID: <20241115113605.1504796-2-alan.maguire@oracle.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20241115113605.1504796-1-alan.maguire@oracle.com> References: <20241115113605.1504796-1-alan.maguire@oracle.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-11-14_05,2024-11-14_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 malwarescore=0 mlxscore=0 bulkscore=0 suspectscore=0 phishscore=0 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2409260000 definitions=main-2411150099 X-Proofpoint-ORIG-GUID: fI58DbZIiHLzONgvfDkYw0omvIja288c X-Proofpoint-GUID: fI58DbZIiHLzONgvfDkYw0omvIja288c From: Eduard Zingerman Song Liu reported that a kernel func (perf_event_read()) cannot be traced in certain situations since the func is not in vmlinux bTF. This happens in kernels 6.4, 6.9 and 6.11 and the kernel is built with pahole 1.27. The perf_event_read() signature in kernel (kernel/events/core.c): static int perf_event_read(struct perf_event *event, bool group) Adding '-V' to pahole command line, and the following error msg can be found: skipping addition of 'perf_event_read'(perf_event_read) due to unexpected register used for parameter Eventually the error message is attributed to the setting (parm->unexpected_reg = 1) in parameter__new() function. The following is the dwarf representation for perf_event_read(): 0x0334c034: DW_TAG_subprogram DW_AT_low_pc (0xffffffff812c6110) DW_AT_high_pc (0xffffffff812c640a) DW_AT_frame_base (DW_OP_reg7 RSP) DW_AT_GNU_all_call_sites (true) DW_AT_name ("perf_event_read") DW_AT_decl_file ("/rw/compile/kernel/events/core.c") DW_AT_decl_line (4641) DW_AT_prototyped (true) DW_AT_type (0x03324f6a "int") 0x0334c04e: DW_TAG_formal_parameter DW_AT_location (0x007de9fd: [0xffffffff812c6115, 0xffffffff812c6141): DW_OP_reg5 RDI [0xffffffff812c6141, 0xffffffff812c6323): DW_OP_reg14 R14 [0xffffffff812c6323, 0xffffffff812c63fe): DW_OP_GNU_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value [0xffffffff812c63fe, 0xffffffff812c6405): DW_OP_reg14 R14 [0xffffffff812c6405, 0xffffffff812c640a): DW_OP_GNU_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value) DW_AT_name ("event") DW_AT_decl_file ("/rw/compile/kernel/events/core.c") DW_AT_decl_line (4641) DW_AT_type (0x0333aac2 "perf_event *") 0x0334c05e: DW_TAG_formal_parameter DW_AT_location (0x007dea82: [0xffffffff812c6137, 0xffffffff812c63f2): DW_OP_reg12 R12 [0xffffffff812c63f2, 0xffffffff812c63fe): DW_OP_GNU_entry_value(DW_OP_reg4 RSI), DW_OP_stack_value [0xffffffff812c63fe, 0xffffffff812c640a): DW_OP_reg12 R12) DW_AT_name ("group") DW_AT_decl_file ("/rw/compile/kernel/events/core.c") DW_AT_decl_line (4641) DW_AT_type (0x03327059 "bool") By inspecting the binary, the second argument ("bool group") is used in the function. The following are the disasm code: ffffffff812c6110 : ffffffff812c6110: 0f 1f 44 00 00 nopl (%rax,%rax) ffffffff812c6115: 55 pushq %rbp ffffffff812c6116: 41 57 pushq %r15 ffffffff812c6118: 41 56 pushq %r14 ffffffff812c611a: 41 55 pushq %r13 ffffffff812c611c: 41 54 pushq %r12 ffffffff812c611e: 53 pushq %rbx ffffffff812c611f: 48 83 ec 18 subq $24, %rsp ffffffff812c6123: 41 89 f4 movl %esi, %r12d <=========== NOTE that here '%esi' is used and moved to '%r12d'. ffffffff812c6126: 49 89 fe movq %rdi, %r14 ffffffff812c6129: 65 48 8b 04 25 28 00 00 00 movq %gs:40, %rax ffffffff812c6132: 48 89 44 24 10 movq %rax, 16(%rsp) ffffffff812c6137: 8b af a8 00 00 00 movl 168(%rdi), %ebp ffffffff812c613d: 85 ed testl %ebp, %ebp ffffffff812c613f: 75 3f jne 0xffffffff812c6180 ffffffff812c6141: 66 2e 0f 1f 84 00 00 00 00 00 nopw %cs:(%rax,%rax) ffffffff812c614b: 0f 1f 44 00 00 nopl (%rax,%rax) ffffffff812c6150: 49 8b 9e 28 02 00 00 movq 552(%r14), %rbx ffffffff812c6157: 48 89 df movq %rbx, %rdi ffffffff812c615a: e8 c1 a0 d7 00 callq 0xffffffff82040220 <_raw_spin_lock_irqsave> ffffffff812c615f: 49 89 c7 movq %rax, %r15 ffffffff812c6162: 41 8b ae a8 00 00 00 movl 168(%r14), %ebp ffffffff812c6169: 85 ed testl %ebp, %ebp ffffffff812c616b: 0f 84 9a 00 00 00 je 0xffffffff812c620b ffffffff812c6171: 48 89 df movq %rbx, %rdi ffffffff812c6174: 4c 89 fe movq %r15, %rsi <=========== NOTE: %rsi is overwritten ...... ffffffff812c63f0: 41 5c popq %r12 <============ POP r12 ffffffff812c63f2: 41 5d popq %r13 ffffffff812c63f4: 41 5e popq %r14 ffffffff812c63f6: 41 5f popq %r15 ffffffff812c63f8: 5d popq %rbp ffffffff812c63f9: e9 e2 a8 d7 00 jmp 0xffffffff82040ce0 <__x86_return_thunk> ffffffff812c63fe: 31 c0 xorl %eax, %eax ffffffff812c6400: e9 be fe ff ff jmp 0xffffffff812c62c3 It is not clear why dwarf didn't encode %rsi in locations. But DW_OP_GNU_entry_value(DW_OP_reg4 RSI) tells us that RSI is live at the entry of perf_event_read(). So this patch tries to search DW_OP_GNU_entry_value/DW_OP_entry_value location/expression so if the expected parameter register matches the register in DW_OP_GNU_entry_value/DW_OP_entry_value, then the original parameter is not optimized. For one of internal 6.11 kernel, there are 62498 functions in BTF and perf_event_read() is not there. With this patch, there are 62552 functions in BTF and perf_event_read() is included. Reported-by: Song Liu Signed-off-by: Yonghong Song Signed-off-by: Eduard Zingerman Signed-off-by: Alan Maguire --- dwarf_loader.c | 106 ++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 83 insertions(+), 23 deletions(-) diff --git a/dwarf_loader.c b/dwarf_loader.c index ec8641b..4789967 100644 --- a/dwarf_loader.c +++ b/dwarf_loader.c @@ -1157,16 +1157,90 @@ static struct template_parameter_pack *template_parameter_pack__new(Dwarf_Die *d return pack; } +/* Returns number of locations found or negative value for errors. */ +static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr, + ptrdiff_t offset, Dwarf_Addr *basep, + Dwarf_Addr *startp, Dwarf_Addr *endp, + Dwarf_Op **expr, size_t *exprlen) +{ + int ret; + +#if _ELFUTILS_PREREQ(0, 157) + ret = dwarf_getlocations(attr, offset, basep, startp, endp, expr, exprlen); +#else + if (offset == 0) { + ret = dwarf_getlocation(attr, expr, exprlen); + if (ret == 0) + ret = 1; + } +#endif + return ret; +} + +/* For DW_AT_location 'attr': + * - if first location is DW_OP_regXX with expected number, return the register; + * otherwise save the register for later return + * - if location DW_OP_entry_value(DW_OP_regXX) with expected number is in the + * list, return the register; otherwise save register for later return + * - otherwise if no register was found for locations, return -1. + */ +static int parameter__reg(Dwarf_Attribute *attr, int expected_reg) +{ + Dwarf_Addr base, start, end; + Dwarf_Op *expr, *entry_ops; + Dwarf_Attribute entry_attr; + size_t exprlen, entry_len; + ptrdiff_t offset = 0; + int loc_num = -1; + int ret = -1; + + while ((offset = __dwarf_getlocations(attr, offset, &base, &start, &end, &expr, &exprlen)) > 0) { + loc_num++; + + /* Convert expression list (XX DW_OP_stack_value) -> (XX). + * DW_OP_stack_value instructs interpreter to pop current value from + * DWARF expression evaluation stack, and thus is not important here. + */ + if (exprlen > 1 && expr[exprlen - 1].atom == DW_OP_stack_value) + exprlen--; + + if (exprlen != 1) + continue; + + switch (expr->atom) { + /* match DW_OP_regXX at first location */ + case DW_OP_reg0 ... DW_OP_reg31: + if (loc_num != 0) + break; + ret = expr->atom; + if (ret == expected_reg) + goto out; + break; + /* match DW_OP_entry_value(DW_OP_regXX) at any location */ + case DW_OP_entry_value: + case DW_OP_GNU_entry_value: + if (dwarf_getlocation_attr(attr, expr, &entry_attr) == 0 && + dwarf_getlocation(&entry_attr, &entry_ops, &entry_len) == 0 && + entry_len == 1) { + ret = entry_ops->atom; + if (ret == expected_reg) + goto out; + } + break; + } + } +out: + return ret; +} + static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, struct conf_load *conf, int param_idx) { struct parameter *parm = tag__alloc(cu, sizeof(*parm)); if (parm != NULL) { - Dwarf_Addr base, start, end; bool has_const_value; Dwarf_Attribute attr; - struct location loc; tag__init(&parm->tag, cu, die); parm->name = attr_string(die, DW_AT_name, conf); @@ -1208,35 +1282,21 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, */ has_const_value = dwarf_attr(die, DW_AT_const_value, &attr) != NULL; parm->has_loc = dwarf_attr(die, DW_AT_location, &attr) != NULL; - /* dwarf_getlocations() handles location lists; here we are - * only interested in the first expr. - */ - if (parm->has_loc && -#if _ELFUTILS_PREREQ(0, 157) - dwarf_getlocations(&attr, 0, &base, &start, &end, - &loc.expr, &loc.exprlen) > 0 && -#else - dwarf_getlocation(&attr, &loc.expr, &loc.exprlen) == 0 && -#endif - loc.exprlen != 0) { + + if (parm->has_loc) { int expected_reg = cu->register_params[param_idx]; - Dwarf_Op *expr = loc.expr; + int actual_reg = parameter__reg(&attr, expected_reg); - switch (expr->atom) { - case DW_OP_reg0 ... DW_OP_reg31: + if (actual_reg < 0) + parm->optimized = 1; + else if (expected_reg >= 0 && expected_reg != actual_reg) /* mark parameters that use an unexpected * register to hold a parameter; these will * be problematic for users of BTF as they * violate expectations about register * contents. */ - if (expected_reg >= 0 && expected_reg != expr->atom) - parm->unexpected_reg = 1; - break; - default: - parm->optimized = 1; - break; - } + parm->unexpected_reg = 1; } else if (has_const_value) { parm->optimized = 1; }