This occurs when gdb sets breakpoints on various probe events in the
dynamic loader. The probe event locations are exported from ld.so as SDT
markers, but gdb needs to know whether ARM or Thumb instructions are
being exported at each marker so that it can insert the appropriate
breakpoint instruction sequence. It does this by mapping the probe
location to a function symbol (see arm_pc_is_thumb in gdb/arm-tdep.c),
and using the target address of the symbol to determine if the function
is called in Thumb or ARM more (bit 0 of the target address will be set
for Thumb mode).
The problem here is that gdb can't map any of the probes to a symbol if
the debug symbols aren't installed, and arm_pc_is_thumb returns false in
this case (indicating ARM instructions).
But the probes that gdb sets breakpoints on are in dl_main, and dl_main is
meant to be called in Thumb mode. See the output of readelf, noting that bit 0
of the target address is set:
$ readelf -s /usr/lib/debug/lib/arm-linux-gnueabihf/ld-2.27.so | grep dl_main
42: 0000172d 10516 FUNC LOCAL DEFAULT 11 dl_main
So without the debug symbols installed, gdb inserts the ARM breakpoint
instruction sequence for the dynamic loader probes, when it should be
inserting the Thumb instruction sequence. This is why it crashes.
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https://bugs.launchpad.net/bugs/1576432
Title:
gdb crashes when trying to start a debugging session
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