From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 93B9C20A5CE for ; Tue, 12 Nov 2024 17:07:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731431270; cv=none; b=XOpqsk/PFIWmSREx5MPqHRtZWhoQ8fwlfCA9a/LE7tOZmNg/KzWvmlkOkuDZyhBOnaZ+gRmxBcE7J1AkhO9z0BNphY9pRiiIh+2SDfesvta218UTKG9dtcAovV1tDXi5duDA6JEcNgEY+cHoE0q0OTOk6HbFCOPAZRLcVwUzP+0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731431270; c=relaxed/simple; bh=ReQnSw+bxPpsKEXNUfGY1wZis1FGzWMZ+p/JQVDw6Fs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rtQsMcilU72K8gQKvXpb+PETv2RPyzJr/6omIvav5DzLjo0pXTw3wPxn1ErqzP9nfonv26ktlfOLcE7oV8tWbyQENIMWMXTNkYhFsQmdV/7+e8jXiSBWffcNnhs4TKHv75/UjMcxxpn0vPDThlGftIqEj5dP/dsUOGhapXUZ2Yo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=MNvP0/gT; arc=none smtp.client-ip=95.215.58.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="MNvP0/gT" Message-ID: <48a2d5a2-38e0-4c36-90cc-122602ff6386@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1731431265; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bK2s3vs44MK62StHOPp6xhc2KA8n6cAVMSCtIx6fpfU=; b=MNvP0/gTIKs807kz6shUbWVGXGEfFc+BbrTdLgEAEGUZgtryAkC+IBF+1LR4TAX0zWXHda IUnXQL+lM/KDFnfEAny601hS7U4wogOPeCEQkI9ELNAgGdoGi7BPsy255U3VfXXdCGBOZI iJONwdHT+WcK7q4e+OpOI+4QRadxanQ= Date: Tue, 12 Nov 2024 09:07:41 -0800 Precedence: bulk X-Mailing-List: dwarves@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH dwarves 3/3] dwarf_loader: Check DW_OP_[GNU_]entry_value for possible parameter matching Content-Language: en-GB To: Alan Maguire , Arnaldo Carvalho de Melo , dwarves@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , bpf@vger.kernel.org, Daniel Borkmann , kernel-team@fb.com, Song Liu References: <20241108180508.1196431-1-yonghong.song@linux.dev> <20241108180524.1198900-1-yonghong.song@linux.dev> <5be88704-1bb0-4332-8626-26e7c908184c@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 11/12/24 8:56 AM, Alan Maguire wrote: > On 12/11/2024 01:51, Yonghong Song wrote: >> >> >> On 11/11/24 7:39 AM, Alan Maguire wrote: >>> On 08/11/2024 18:05, Yonghong Song wrote: >>>> 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 matchs 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 61552 >>>> functions >>>> in BTF and perf_event_read() is included. >>>> >>> hi Yonghong, >>> >>> I'm confused by these numbers. I would have thought your changes would >>> have led to a net increase of functions encoded in vmlinux BTF since we >>> are now likely catching more cases where registers are expected.  When I >>> ran your patches against an LLVM-built kernel, that's what I saw; 70 >>> additional functions were recognized as having expected parameters, and >>> thus were encoded in BTF. In your case it looks like we lost nearly 1000 >>> functions. Any idea what's going on there? If you can share your config, >>> LLVM version I can dig into this from my side too. Thanks! >> Attached is my config (based on one of meta internal configs). I tried >> with master branch with head: >> >> 7b6e5bfa2541380b478ea1532880210ea3e39e11 (HEAD -> master, origin/master, >> origin/HEAD) Merge branch 'refactor-lock-management' >> ae6e3a273f590a2b64f14a9fab3546c3a8f44ed4 bpf: Drop special callback >> reference handling >> f6b9a69a9e56b2083aca8a925fc1a28eb698e3ed bpf: Refactor active lock >> management >> >> I am using pahole v1.27. >> >> I am using an llvm built from upstream. The following is llvm-project head: >> beb12f92c71981670e07e47275efc6b5647011c1 (HEAD -> main) [RISCV] Add >> +optimized-nfN-segment-load-store (#114414) >> 6bad4514c938b3b48c0c719b8dd98b3906f2c290 [AArch64] Extend vector mull >> test coverage. NFC >> 915b910d800d7fab6a692294ff1d7075d8cba824 [libc] Fix typos in proxy type >> headers (#114717) >> 98ea1a81a28a6dd36941456c8ab4ce46f665f57a [IPO] Remove unused includes >> (NFC) (#114716) >> >> With the above setup, when to do >> >> pahole -JV -- >> btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func,decl_tag_kfuncs vmlinux >& log.pahole >> >> You will find the below info in the log: >>   skipping addition of 'perf_event_read'(perf_event_read) due to >> unexpected register used for paramet >> >> In the dwarf: >> >> 0x02122746:   DW_TAG_subprogram >>                 DW_AT_low_pc    (0xffffffff81299740) >>                 DW_AT_high_pc   (0xffffffff812999f7) >>                 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 ("/home/yhs/work/bpf-next/kernel/events/ >> core.c") >>                 DW_AT_decl_line (4746) >>                 DW_AT_prototyped        (true) >>                 DW_AT_type      (0x020f95f5 "int") >> >> 0x02122760:     DW_TAG_formal_parameter >>                   DW_AT_location        (0x00769b72: >>                      [0xffffffff81299745, 0xffffffff81299764): >> DW_OP_reg5 RDI >>                      [0xffffffff81299764, 0xffffffff81299937): >> DW_OP_reg3 RBX >>                      [0xffffffff81299937, 0xffffffff812999f0): >> DW_OP_GNU_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value >>                      [0xffffffff812999f0, 0xffffffff812999f7): >> DW_OP_reg3 RBX) >>                   DW_AT_name    ("event") >>                   DW_AT_decl_file       ("/home/yhs/work/bpf-next/ >> kernel/events/core.c") >>                   DW_AT_decl_line       (4746) >>                   DW_AT_type    (0x0210f654 "perf_event *") >>                     0x02122770:     DW_TAG_formal_parameter >>                   DW_AT_location        (0x00769c61: >>                      [0xffffffff81299758, 0xffffffff81299926): >> DW_OP_reg6 RBP >>                      [0xffffffff81299926, 0xffffffff812999f0): >> DW_OP_GNU_entry_value(DW_OP_reg4 RSI), DW_OP_stack_value >>                      [0xffffffff812999f0, 0xffffffff812999f7): >> DW_OP_reg6 RBP) >>                   DW_AT_name    ("group") >>                   DW_AT_decl_file       ("/home/yhs/work/bpf-next/ >> kernel/events/core.c") >> >> The above is slightly different from our production kernel where Song >> reported. But essence is the same. >> The second parameter needs to check DW_OP_GNU_entry_value(DW_OP_reg4 >> RSI) to ensure the second >> argument is available. >> >> My patch is supposed to only make improvement. I am curiously why you >> get less functions encoded in BTF. >> > Thanks for the config etc! When I build bpf-next using master branch > llvm and this config, I see > > with baseline (master branch pahole): 62371 functions, no perf_event_read > your series on top of master branch pahole: 62433 functions, > perf_event_read present > > So that's consistent with what I've seen with other configs; more > functions are present in vmlinux BTF since we are now seeing more cases > where parameters are in fact consistent. The part that confuses me > though is the numbers you initially reported above > > "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 61552 > functions in BTF and perf_event_read() is included." > > These numbers suggest you lost nearly 1000 functions when building > vmlinux BTF with pahole using this series. That's the part I don't > understand - we should just see a gain in numbers of functions in > vmlinux BTF, right? Did you mean 62552 functions rather than 61552 perhaps? Sorry, really embarrassing. it is typo. Indeed it should be 62552 functions in BTF instead. > > Alan > >>> Alan >>> >>>> Reported-by: Song Liu >>>> Signed-off-by: Yonghong Song >>>> --- >>>>   dwarf_loader.c | 81 +++++++++++++++++++++++++++++++++++--------------- >>>>   1 file changed, 57 insertions(+), 24 deletions(-) >>>> >> [...]