rust executables with gdb 7.12+ can't display register values (gdb bug) about gdbgui HOT 6 CLOSED

Turns out the pipe is broken because gdb segfaults and the process exits (becomes defunct/zombie). The segfault only occurs when debugging a rust program under pygdbmi, not when running directly from gdb's commandline, or debugging any other language.

The dmesg log shows

[ 4467.187888] gdb[13609]: segfault at 0 ip 00000000006489ed sp 00007ffc0a0ce260 error 4 in gdb[400000+617000]

Running again with strace output logged yields this as the last line.

ptrace(PTRACE_GETREGSET, 14037, NT_X86_XSTATE, [{0x7ffe8bb4ee20, 832}]) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0} ---
+++ killed by SIGSEGV +++

See attached file gdb_strace.txt for the full strace log.

Tagging @o11c in case you have any ideas on steps forward.

from gdbgui.

Interesting. Didn't expect a segfault to be the reason. Will be watching this.

from gdbgui.

The segfault occurs in -data-list-register-values x regardless of whether it's run as a subprocess or not. The bug was fixed in gdb's [git repository](git clone git://sourceware.org/git/binutils-gdb.git), commit b96645f1a1e608 "Add support for untagged unions in Rust".

The HEAD of gdb's master branch does not have this bug, so the next gdb release (version 8) should have this issue fixed. For now, I will add a warning to gdbgui, and disable the -data-list-register-values x if gdbgui was able to determine rust source files were used to compile the executable.

Bug filed with gdb: https://sourceware.org/bugzilla/show_bug.cgi?id=21450

from gdbgui.

@sharazam I added logic to prevent gdbgui from fetching register values when using gdb 7.12.x and debugging a Rust executable, which avoids the segfault. gdbgui also displays a warning to users that this is occurring. If you ever get tired of the TUI and want to try gdbgui again, you can upgrade it and it should work for your rust program.

from gdbgui.

Can you still fetch the values using -var-create $registername?

from gdbgui.

Doesn't seem to be valid syntax:

-var-create rax
-var-create: Usage: NAME FRAME EXPRESSION.

however info registers works

info registers
rax 0x7fffffffdfd0
 140737488347088

rbx 0x0
 0

rcx 0x604028
 6307880

from gdbgui.