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Date: Sat, 4 Mar 2017 21:41:24 -0600 (CST)
From: Paul Sturm <psturm@...putervoice.com>
To: musl <musl@...ts.openwall.com>
Subject: Re: Static PIE with musl and clang
OK. I tried to compile this program:
#include <stdio.h>
int main() {
printf("%p\n", main);
return 0;
}
Command line:
clang /usr/lib/rcrt1.o ../aslr.c -o aslr -fPIE -shared -Bsymbolic -Wl,--no-dynamic-linker
./aslr seg faults when I run it.
readelf -e aslr looks like this:
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: DYN (Shared object file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x788
Start of program headers: 64 (bytes into file)
Start of section headers: 6584 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 6
Size of section headers: 64 (bytes)
Number of section headers: 26
Section header string table index: 23
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .hash HASH 0000000000000190 00000190
0000000000000058 0000000000000004 A 2 0 8
[ 2] .dynsym DYNSYM 00000000000001e8 000001e8
0000000000000198 0000000000000018 A 3 1 8
[ 3] .dynstr STRTAB 0000000000000380 00000380
00000000000000de 0000000000000000 A 0 0 1
[ 4] .rela.dyn RELA 0000000000000460 00000460
00000000000000f0 0000000000000018 A 2 0 8
[ 5] .rela.plt RELA 0000000000000550 00000550
0000000000000048 0000000000000018 AI 2 19 8
[ 6] .init PROGBITS 0000000000000598 00000598
000000000000000d 0000000000000000 AX 0 0 1
[ 7] .plt PROGBITS 00000000000005b0 000005b0
0000000000000040 0000000000000010 AX 0 0 16
[ 8] .plt.got PROGBITS 00000000000005f0 000005f0
0000000000000018 0000000000000000 AX 0 0 8
[ 9] .text PROGBITS 0000000000000610 00000610
0000000000000497 0000000000000000 AX 0 0 16
[10] .fini PROGBITS 0000000000000aa7 00000aa7
0000000000000008 0000000000000000 AX 0 0 1
[11] .rodata PROGBITS 0000000000000aaf 00000aaf
0000000000000004 0000000000000001 AMS 0 0 1
[12] .eh_frame_hdr PROGBITS 0000000000000ab4 00000ab4
000000000000001c 0000000000000000 A 0 0 4
[13] .eh_frame PROGBITS 0000000000000ad0 00000ad0
0000000000000064 0000000000000000 A 0 0 8
[14] .ctors PROGBITS 0000000000200e40 00000e40
0000000000000010 0000000000000000 WA 0 0 8
[15] .dtors PROGBITS 0000000000200e50 00000e50
0000000000000010 0000000000000000 WA 0 0 8
[16] .jcr PROGBITS 0000000000200e60 00000e60
0000000000000008 0000000000000000 WA 0 0 8
[17] .dynamic DYNAMIC 0000000000200e68 00000e68
0000000000000150 0000000000000010 WA 3 0 8
[18] .got PROGBITS 0000000000200fb8 00000fb8
0000000000000048 0000000000000008 WA 0 0 8
[19] .got.plt PROGBITS 0000000000201000 00001000
0000000000000030 0000000000000008 WA 0 0 8
[20] .data PROGBITS 0000000000201030 00001030
0000000000000008 0000000000000000 WA 0 0 8
[21] .bss NOBITS 0000000000201040 00001038
0000000000000050 0000000000000000 WA 0 0 32
[22] .comment PROGBITS 0000000000000000 00001038
000000000000003c 0000000000000001 MS 0 0 1
[23] .shstrtab STRTAB 0000000000000000 000018fb
00000000000000b9 0000000000000000 0 0 1
[24] .symtab SYMTAB 0000000000000000 00001078
0000000000000648 0000000000000018 25 51 8
[25] .strtab STRTAB 0000000000000000 000016c0
000000000000023b 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
l (large), p (processor specific)
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000b34 0x0000000000000b34 R E 200000
LOAD 0x0000000000000e40 0x0000000000200e40 0x0000000000200e40
0x00000000000001f8 0x0000000000000250 RW 200000
DYNAMIC 0x0000000000000e68 0x0000000000200e68 0x0000000000200e68
0x0000000000000150 0x0000000000000150 RW 8
GNU_EH_FRAME 0x0000000000000ab4 0x0000000000000ab4 0x0000000000000ab4
0x000000000000001c 0x000000000000001c R 4
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 10
GNU_RELRO 0x0000000000000e40 0x0000000000200e40 0x0000000000200e40
0x00000000000001c0 0x00000000000001c0 R 1
Section to Segment mapping:
Segment Sections...
00 .hash .dynsym .dynstr .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame
01 .ctors .dtors .jcr .dynamic .got .got.plt .data .bss
02 .dynamic
03 .eh_frame_hdr
04
05 .ctors .dtors .jcr .dynamic .got
From: "dalias" <dalias@...c.org>
To: "musl" <musl@...ts.openwall.com>
Sent: Sunday, March 5, 2017 2:44:03 AM
Subject: Re: [musl] Static PIE with musl and clang
On Sat, Mar 04, 2017 at 07:47:31PM -0600, Paul Sturm wrote:
> Has anyone managed to build static PIE with musl and clang,
> preferably linking with lld?
>
> I see that this has been done using GCC and rcrt1.o, but I cannot
> find a combination of command line parameters that will successfully
> link and execute with clang.
>
> I am using clang 4.0.0RC2 and musl 1.1.16. I have also tried to use
> binutils ld instead of llvm lld to no avail.
I doubt lld can do it yet; you need some equivalent of the
--no-dynamic-linker option I added to BFD ld. It should be possible
with clang using binutils/BFD ld. You might also be able to hack it by
using -shared -Bsymbolic and explicitly linking rcrt1.o on the link
command line (essentially doing the same thing you'd do to make an
executable shared library) but there are corner-case things that break
when you try to do it this way. The right approach would be adding
--no-dynamic-linker to lld and teaching clang to pass it when linking
with -static -pie.
Rich
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