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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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