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DescriptionCarlos O'Donell
2022-03-08 17:05:55 UTC
Description of problem:
gdb is unable to parse sdt probe arguments in xmm registers.
Version-Release number of selected component (if applicable):
gdb 10.2-9.el9
How reproducible:
Always reproducible. Use a simple pthread_create/pthread_join example and then:
break main
start
info probes stap libc
break *[address of probe for pthread_start]
continue
show convenience
...
$_probe_arg11 = <error: Invalid probe argument 11 -- probe has 3 arguments available>
$_probe_arg10 = <error: Invalid probe argument 10 -- probe has 3 arguments available>
$_probe_arg9 = <error: Invalid probe argument 9 -- probe has 3 arguments available>
$_probe_arg8 = <error: Invalid probe argument 8 -- probe has 3 arguments available>
$_probe_arg7 = <error: Invalid probe argument 7 -- probe has 3 arguments available>
$_probe_arg6 = <error: Invalid probe argument 6 -- probe has 3 arguments available>
$_probe_arg5 = <error: Invalid probe argument 5 -- probe has 3 arguments available>
$_probe_arg4 = <error: Invalid probe argument 4 -- probe has 3 arguments available>
$_probe_arg3 = <error: Invalid probe argument 3 -- probe has 3 arguments available>
$_probe_arg2 = 0
$_probe_arg1 = 4198902
$_probe_arg0 = <error: Invalid cast.>
^^^^^^^^^^^^^^^^^^^^^^ Broken due to xmmo0 usage.
$_probe_argc = 3
$_probe_arg2 is 0 because NULL was passed as the arg to pthread_create().
-- Works because it's 8@1608(%rbx)
$_probe_arg1 is the correct address of the start function e.g. 0x4011f6 <worker>
-- Works because it's 8@1600(%rbx)
$_probe_arg0 is broken in gdb because of the use of xmm0.
-- Doesn't work because 8@%xmm0 uses %xmm0.
This is a blocker IMO since probes using xmm0 looks broken in gdb too.
Actual results:
- Prints <erro: Invalid cast.>
Expected results:
- Prints the value.
I've posted this patch to the upstream gdb mailing list:
https://sourceware.org/pipermail/gdb-patches/2022-March/186632.html
This patch allows a user to stop at a probe and view the argument in an xmm register.
What's missing in this patch is GDB's agent expression support (used for the fast tracepoints), so a user can't place a tracepoint at a probe (that uses xmm registers) and collect the arguments. I want to see how the approach I'm proposing in that patch goes down before I start worrying about agent expression support.
Comment 5RHEL Program Management
2023-09-08 07:28:40 UTC
After evaluating this issue, there are no plans to address it further or fix it in an upcoming release. Therefore, it is being closed. If plans change such that this issue will be fixed in an upcoming release, then the bug can be reopened.
Description of problem: gdb is unable to parse sdt probe arguments in xmm registers. Version-Release number of selected component (if applicable): gdb 10.2-9.el9 How reproducible: Always reproducible. Use a simple pthread_create/pthread_join example and then: break main start info probes stap libc break *[address of probe for pthread_start] continue show convenience ... $_probe_arg11 = <error: Invalid probe argument 11 -- probe has 3 arguments available> $_probe_arg10 = <error: Invalid probe argument 10 -- probe has 3 arguments available> $_probe_arg9 = <error: Invalid probe argument 9 -- probe has 3 arguments available> $_probe_arg8 = <error: Invalid probe argument 8 -- probe has 3 arguments available> $_probe_arg7 = <error: Invalid probe argument 7 -- probe has 3 arguments available> $_probe_arg6 = <error: Invalid probe argument 6 -- probe has 3 arguments available> $_probe_arg5 = <error: Invalid probe argument 5 -- probe has 3 arguments available> $_probe_arg4 = <error: Invalid probe argument 4 -- probe has 3 arguments available> $_probe_arg3 = <error: Invalid probe argument 3 -- probe has 3 arguments available> $_probe_arg2 = 0 $_probe_arg1 = 4198902 $_probe_arg0 = <error: Invalid cast.> ^^^^^^^^^^^^^^^^^^^^^^ Broken due to xmmo0 usage. $_probe_argc = 3 $_probe_arg2 is 0 because NULL was passed as the arg to pthread_create(). -- Works because it's 8@1608(%rbx) $_probe_arg1 is the correct address of the start function e.g. 0x4011f6 <worker> -- Works because it's 8@1600(%rbx) $_probe_arg0 is broken in gdb because of the use of xmm0. -- Doesn't work because 8@%xmm0 uses %xmm0. This is a blocker IMO since probes using xmm0 looks broken in gdb too. Actual results: - Prints <erro: Invalid cast.> Expected results: - Prints the value.