gnome-shell segfault in g_strsplit() on RISC-V

Waiting on the retracers... In the meantime, what does the journal say around the time of the crash?

Here is the output of journalctl. The crash is in line 1807.

Still waiting on the retracers to analyse CoreDump.gz

BTW, I would expect Wayland to work at least as easily as Xorg. Any reason why Wayland seems to be disabled?

apport-retrace shows the following:

[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/riscv64-linux-gnu/libthread_db.so.1".
Core was generated by `/usr/bin/gnome-shell'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 __GI_strchr (s=s@entry=0x13ea <error: Cannot access memory at address 0x13ea>, c_in=c_in@entry=58) at ./string/strchr.c:47
47 ./string/strchr.c: No such file or directory.
[Current thread is 1 (Thread 0x3f9a6f7020 (LWP 1053))]
(gdb) up
#1 0x0000003f9dd4891e in __GI_strstr (haystack=0x13ea <error: Cannot access memory at address 0x13ea>, needle=0x2ae7f53538 ":") at ./string/strstr.c:84
84 ./string/strstr.c: No such file or directory.
(gdb) up
#2 0x0000003f9e213314 in g_strsplit () from /lib/riscv64-linux-gnu/libglib-2.0.so.0
(gdb) up
#3 0x0000002ae7f5303a in ?? ()
(gdb) up
Initial frame selected; you cannot go up.
(gdb)

It looks like there is code calling g_strsplit(0x13ea, ":",) and while there are calls of that form in both mutter and gnome-shell, only one in gnome-shell is suspicious:

  maybe_add_rpath_introspection_paths()

It's trying to do ELF parsing. To avoid that code path, try building gnome-shell without the option HAVE_EXE_INTROSPECTION.

Also try running 'mutter --wayland' in a VT so we can rule out mutter.

I rebuilt the gnome shell package with this patch

Index: gnome-shell-44.0/meson.build
===================================================================
--- gnome-shell-44.0.orig/meson.build
+++ gnome-shell-44.0/meson.build
@@ -148,7 +148,7 @@ cdata.set('HAVE_FDWALK', cc.has_function
 cdata.set('HAVE_MALLINFO', cc.has_function('mallinfo'))
 cdata.set('HAVE_MALLINFO2', cc.has_function('mallinfo2'))
 cdata.set('HAVE_SYS_RESOURCE_H', cc.has_header('sys/resource.h'))
-cdata.set('HAVE_EXE_INTROSPECTION',
+cdata.set('HAVE_EXE_INTROSPECTION', false and
   cc.has_header('elf.h') and cc.has_header('link.h'))
 cdata.set('HAVE__NL_TIME_FIRST_WEEKDAY',
   cc.has_header_symbol('langinfo.h', '_NL_TIME_FIRST_WEEKDAY')

With this change gdm3 works as expected using X11.

Wayland works fine too with the patch.

\o/

Should we check CMAKE_SYSTEM_PROCESSOR here and disable introspection on riscv64 only?

Before doing a workaround I want to see if upstream have some ideas:
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6528

We could also investigate the offending function to see if it is sane for all architectures.

I have been single stepping through maybe_add_rpath_introspection_paths() on riscv64.

strtab is set from this value of dyn:

dyn = {
 .d_tag = 0x5,
 .dun = { .d_val = 0xbe8, .d_ptr = 0xbe8},
}

dyn.dptr is not a valid pointer in memory.

obdump -S -D /usr/bin/gnome_shell shows

* section .dynstr starting at 0xbe8.
* section .dynamic starting at 0x4d50

But this does not imply that the sections are loaded to these addresses.
The value of _DYNAMIC on my system was 0x2aaaaed50 and not 0x4d50.

On arm64 the value of dyn.dptr is a relocated value and not the one from the binary before relocation.

For RISC-V and MIPS DL_RO_DYN_SECTION is defined as 1. Hence the .dynamic section is not relocated in glibc's function elf_get_dynamic_section().

See

sysdeps/riscv/dl-relocate-ld.h:23:
#define DL_RO_DYN_SECTION 1

sysdeps/mips/dl-relocate-ld.h:23:
#define DL_RO_DYN_SECTION 1

According to the code comment "The dynamic section is readonly for ABI compatibility" we cannot expect glibc to change the behavior in future.

Cf. https://patchwork.ozlabs<email address hidden>/

Please test: https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2718.patch

For the record there are no retracers for riscv64 yet.

This bug was fixed in the package gnome-shell - 44.0-2ubuntu3

---------------
gnome-shell (44.0-2ubuntu3) lunar; urgency=medium

  * Cherry-pick fix for installing extensions (LP: #2013073)
  * Add proposed patch to fix running gnome-shell on RISC-V (LP: #2012068)

 -- Jeremy Bicha <email address hidden> Fri, 31 Mar 2023 10:18:23 -0400