[yocto] gdb built with musl libc segfault

[Paul Barker]

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.

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?

-- 
Paul Barker
Managing Director & Principal Engineer
Beta Five Ltd