Date: Thu, 9 Jun 2016 00:36:20 +0300 (MSK) From: Alexander Monakov <amonakov@...ras.ru> To: fREW Schmidt <frioux@...il.com> cc: Andy Lutomirski <luto@...capital.net>, Linux Kernel <linux-kernel@...r.kernel.org>, musl@...ts.openwall.com Subject: Re: Broken vDSO on built kernel On Wed, 8 Jun 2016, fREW Schmidt wrote: > I was debugging an issue I ran into ( > https://github.com/docker/docker/issues/23378) and after chatting with the > folks in #musl and we triaged it down to a broken vDSO (tested by running > `strace date` and seeing a clock_gettime call.) To provide a bit more detail, we've found that the vdso mappend into the application has no dynamic symbols; Glibc ignores the vdso, so it continues to work, but musl segfaults since the vdso is invalid. I'm pasting below `readelf -aW` output on the vdso dumped on the affected system (via 'fwrite((void*)getauxval(AT_SYSINFO_EHDR), 8192, 1, stdout)'; as you can see, there's no dynamic symbols and symbol hash tables. It may be a toolchain bug since there was no issue with 4.6 kernel (and reportedly there were no significant vdso changes merged into 4.7 -- the issue is seen on Ubuntu's 4.7rc2). Alexander ELF Header: Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 Class: ELF64 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) Machine: Advanced Micro Devices X86-64 Version: 0x1 Entry point address: 0x600 Start of program headers: 64 (bytes into file) Start of section headers: 2976 (bytes into file) Flags: 0x0 Size of this header: 64 (bytes) Size of program headers: 56 (bytes) Number of program headers: 4 Size of section headers: 64 (bytes) Number of section headers: 10 Section header string table index: 9 Section Headers: [Nr] Name Type Address Off Size ES Flg Lk Inf Al [ 0] NULL 0000000000000000 000000 000000 00 0 0 0 [ 1] .rodata PROGBITS 0000000000000120 000120 000340 00 WA 0 0 1 [ 2] .note NOTE 0000000000000460 000460 00003c 00 A 0 0 4 [ 3] .eh_frame_hdr PROGBITS 000000000000049c 00049c 00003c 00 A 0 0 4 [ 4] .eh_frame PROGBITS 00000000000004d8 0004d8 000120 00 A 0 0 8 [ 5] .text PROGBITS 0000000000000600 000600 0004c9 00 AX 0 0 16 [ 6] .altinstructions PROGBITS 0000000000000ac9 000ac9 000034 00 A 0 0 1 [ 7] .altinstr_replacement PROGBITS 0000000000000afd 000afd 00000c 00 AX 0 0 1 [ 8] .comment PROGBITS 0000000000000000 000b09 00002e 01 MS 0 0 1 [ 9] .shstrtab STRTAB 0000000000000000 000b37 000067 00 0 0 1 Key to Flags: W (write), A (alloc), X (execute), M (merge), S (strings), l (large) I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown) O (extra OS processing required) o (OS specific), p (processor specific) There are no section groups in this file. Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x000b09 0x000b09 R E 0x1000 DYNAMIC 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0x8 NOTE 0x000460 0x0000000000000460 0x0000000000000460 0x00003c 0x00003c R 0x4 GNU_EH_FRAME 0x00049c 0x000000000000049c 0x000000000000049c 0x00003c 0x00003c R 0x4 Section to Segment mapping: Segment Sections... 00 .rodata .note .eh_frame_hdr .eh_frame .text .altinstructions .altinstr_replacement 01 02 .note 03 .eh_frame_hdr There is no dynamic section in this file. There are no relocations in this file. The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported. No version information found in this file. Displaying notes found at file offset 0x00000460 with length 0x0000003c: Owner Data size Description Linux 0x00000004 Unknown note type: (0x00000000) GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring) Build ID: 496e9db3f494533ffaaf39737eb1023938861349
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