[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250301160241.GQ1827@brightrain.aerifal.cx>
Date: Sat, 1 Mar 2025 11:02:42 -0500
From: Rich Felker <dalias@...c.org>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: musl@...ts.openwall.com
Subject: Re: Support for -static-pie relocations
On Sat, Mar 01, 2025 at 04:08:52PM +0100, Dmitry Vyukov wrote:
> Hello,
>
> This simple program crashes when compiled with -static-pie:
>
> #include <stdio.h>
> int main() { fprintf(stderr, "Hello\n"); }
Not reproducible here. Could you include details on how the toolchain
was built and what compile/link command lines were used?
> Program received signal SIGSEGV, Segmentation fault.
> 0x0000000000001170 in ?? ()
> (gdb) bt
> #0 0x0000000000001170 in ?? ()
> #1 0x00007ffff7ffb3b8 in libc_start_init () at src/env/__libc_start_main.c:64
> #2 0x00007ffff7ffb3e8 in libc_start_main_stage2 (main=0x7ffff7ffb180
> <main>, argc=1, argv=0x7fffffffdc98)
> at src/env/__libc_start_main.c:92
> #3 0x00007ffff7ffb0b1 in _start ()
>
> (gdb) up
> #1 0x00007ffff7ffb3b8 in libc_start_init () at src/env/__libc_start_main.c:64
> 64 (*(void (**)(void))a)();
>
> (gdb) disass
> Dump of assembler code for function libc_start_init:
> 0x00007ffff7ffb39b <+0>: push %rbp
> 0x00007ffff7ffb39c <+1>: push %rbx
> 0x00007ffff7ffb39d <+2>: sub $0x8,%rsp
> 0x00007ffff7ffb3a1 <+6>: call 0x7ffff7ffb000 <_init>
> 0x00007ffff7ffb3a6 <+11>: lea 0x2a9b(%rip),%rbx # 0x7ffff7ffde48
> 0x00007ffff7ffb3ad <+18>: lea 0x2a9c(%rip),%rbp # 0x7ffff7ffde50
> 0x00007ffff7ffb3b4 <+25>: jmp 0x7ffff7ffb3bc <libc_start_init+33>
> 0x00007ffff7ffb3b6 <+27>: call *(%rbx)
> => 0x00007ffff7ffb3b8 <+29>: add $0x8,%rbx
> 0x00007ffff7ffb3bc <+33>: cmp %rbp,%rbx
> 0x00007ffff7ffb3bf <+36>: jb 0x7ffff7ffb3b6 <libc_start_init+27>
> 0x00007ffff7ffb3c1 <+38>: add $0x8,%rsp
> 0x00007ffff7ffb3c5 <+42>: pop %rbx
> 0x00007ffff7ffb3c6 <+43>: pop %rbp
> 0x00007ffff7ffb3c7 <+44>: ret
> End of assembler dump.
>
> (gdb) p /x $rbx
> $1 = 0x7ffff7ffde48
> (gdb) p /x *(void**)$rbx
> $2 = 0x1170
>
> This 0x1170 is probably a ctor pointer offset that wasn't relocated.
Yes that looks plausible.
> A fix would probably be calling _dl_relocate_object() somewhere on the
> __libc_start_main() path.
Relocations are processed in the crt entry point before
__libc_start_main is reached. The relevant code is ldso/dlstart.c.
Perhaps you're using newer tooling that's encoding some or all of the
relocations in some unsupported manner? For example I think using musl
1.2.3 (pre RELR addition) rcrt1.o along with a newer binutils that's
been configured to default to RELR encoding would produce the failure
you're seeing.
Rich
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
