Re: [musl] printf segfaults on recent musl versions

[Sagar Tiwari <fctorial@gmail.com>]

I'm assembling a file with clang and linking it to custom compiled
musl with ld. This is the project I'm using:

https://drive.google.com/file/d/1RiKZTf_nJUak14fz7kSXbh7egJuDthDk/view?usp=sharing

musl 1.1.8 is the last version that works with this project. I used
clang 11.0.0 to compile both musl and this project.

On 11/01/2021, Rich Felker <dalias@libc.org> wrote:
> On Mon, Jan 11, 2021 at 10:31:21PM +0530, Sagar Tiwari wrote:
>> Hi,
>>
>> Apologies if this isn't a support forum for musl. I couldn't find any
>> such portal online.
>>
>> I'm trying to compile a program with musl libc. Dynamically linked
>> version of this program works fine, but the statically linked version
>> segfaults whenever `printf` is invoked. This is how a debugging
>> session looks like:
>>
>> <pre>
>> $ gdb out/sm
>> GNU gdb (GDB) 9.2
>> Copyright (C) 2020 Free Software Foundation, Inc.
>> License GPLv3+: GNU GPL version 3 or later
>> <http://gnu.org/licenses/gpl.html>
>> This is free software: you are free to change and redistribute it.
>> There is NO WARRANTY, to the extent permitted by law.
>> Type "show copying" and "show warranty" for details.
>> This GDB was configured as "x86_64-unknown-linux-gnu".
>> Type "show configuration" for configuration details.
>> For bug reporting instructions, please see:
>> <http://www.gnu.org/software/gdb/bugs/>.
>> Find the GDB manual and other documentation resources online at:
>>     <http://www.gnu.org/software/gdb/documentation/>.
>>
>> For help, type "help".
>> Type "apropos word" to search for commands related to "word"...
>> Reading symbols from out/sm...
>> (gdb) b printf
>> Breakpoint 1 at 0x100ac: file src/stdio/printf.c, line 5.
>> (gdb) r
>> Starting program: /home/fctorial/src/pgs/c/out/sm
>>
>> Breakpoint 1, printf (fmt=0x1004f <msg1> "hello world from printf\n")
>> at src/stdio/printf.c:5
>> 5       {
>> (gdb) n
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> 0x000000000001010a in printf (fmt=0x1004f <msg1> "hello world from
>> printf\n") at src/stdio/printf.c:5
>> 5       {
>> (gdb) quit
>> A debugging session is active.
>>
>>         Inferior 1 [process 25984] will be killed.
>>
>> Quit anyway? (y or n) EOF [assumed Y]
>>
>> </pre>
>>
>> This issue appears when linking with recent musl versions (within an
>> year). 1.0.0 doesn't have this issue. I can call other functions like
>> 'rand', 'strlen' without any issue. `printf` and `puts` are
>> segfaulting.
>
> Can you elaborate on how you compiled/linked (using musl-gcc wrapper?
> mcm-built or distro-provided toolchain or one you built yourself?
> etc.)
>
> Judging from the very low address in gdb output, my guess is that you
> have a broken toolchain that's trying to link static pie without using
> the right link options or start files.
>
> Rich
>