[yocto] gdb built with musl libc segfault

[Lluis Campos]

Hi Paul,


On 02.04.2019 14:49, Paul Barker wrote:
> On 02/04/2019 12:45, Lluis Campos wrote:
>> Hi all,
>>
>> This is my very first question in the Yocto mailing list. Very 
>> exited! Please let me know if I should use other list for this.
>>
>>
>> I am building an image using musl libc instead of gnu libc. I am not 
>> using yocto-tiny distro, instead I achieve this by setting on my 
>> local.conf:
>>
>> TCLIBC = "musl"
>>
>>
>> My app (mender) got a segfault just starting. See output from strace:
>>
>> root at raspberrypi3:~# strace mender
>> execve("/usr/bin/mender", ["mender"], 0x7ee65e10 /* 13 vars */) = 0
>> set_tls(0x76f1bffc)                     = 0
>> set_tid_address(0x76f1bfa0)             = 3020
>> --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_ACCERR, si_addr=0x530bc8} 
>> ---
>> +++ killed by SIGSEGV +++
>> Segmentation fault
>>
>>
>> To be able to debug the process, I added gdb to my image adding to my 
>> local.conf:
>>
>> CORE_IMAGE_EXTRA_INSTALL += "packagegroup-core-buildessential 
>> packagegroup-core-tools-debug"
>>
>>
>> Then, ironically, gdb itself also segfaults:
>>
>> root at raspberrypi3:~# strace gdb 2>&1 | tail
>> fcntl64(3, F_SETFD, FD_CLOEXEC)         = 0
>> getdents64(3, /* 6 entries */, 2048)    = 144
>> getdents64(3, /* 0 entries */, 2048)    = 0
>> close(3)                                = 0
>> ioctl(0, TIOCGWINSZ, {ws_row=25, ws_col=74, ws_xpixel=0, 
>> ws_ypixel=0}) = 0
>> getcwd("/home/root", 4096)              = 11
>> access("/usr/local/bin/gdb", X_OK)      = -1 ENOENT (No such file or 
>> directory)
>> access("/usr/bin/gdb", X_OK)            = 0
>> --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, 
>> si_addr=0x7e35aff0} ---
>> +++ killed by SIGSEGV +++
>>
>>
>> So, what is going on here? My guess is that some recipes are being 
>> wrongly linked with gnu libc instead of musl, and then cannot run in 
>> my device.
>>
>> Any ideas on how to debug the issue?
>>
>
> Hi Lluis,
>
> This is an issue I've seen before with runc and gdb.
>
> In runc we saw SIGILL which I tracked down to some hideous 
> setjmp/longjmp magic written in C. cgo is used to include this C code 
> in with the Go code that comprises the rest of the application.

Our application is written in Go and we use CGO as well. So it sounds 
quite similar.


>
> In gdb we saw SIGSEGV which is what you've got above.
>
> I think things are being correctly linked against musl but then 
> there's some runtime issue in recent musl versions, possibly in 
> conjunction with recent kernel headers.
>
> Are you using the thud or master branch?
>
I am using thud branch. I haven't actually tried with master but I will 
do it later today


Thanks,

Lluís