Re: [PATCH] selftests/powerpc/tm: Fix tcheck() reading uninitialised CR value

[Venkat <venkat88@linux.ibm.com>]

> On 8 Sep 2026, at 3:24 AM, Thibault Ferrante <thibault.ferrante@canonical.com> wrote:
> 
> tcheck() is used to check the current transaction state (active,
> suspended, doomed) via the "tcheck" instruction, which writes its
> result into CR field 0. The inline asm declared a GPR output operand
> for this result but never actually moved the CR into it.
> 
> Every caller (tcheck_doomed(), tcheck_active(), tcheck_suspended(),
> tcheck_transactional()) has effectively been testing bits of an unrelated,
> arbitrary register value since this helper was introduced.
> The "& 4" mask discards the TDOOMED and TS_lsb (suspended) bits before
> they ever reach the callers, so tcheck_doomed() and tcheck_suspended()
> can never return true, and tcheck_transactional() degrades to being
> equivalent to tcheck_active().
> 
> Fix tcheck() to actually move CR into the output register with mfcr,
> and widen the mask from "& 4" to "& 0xf" so the full CR0 nibble
> (TDOOMED | TS_msb | TS_lsb | reserved) is preserved for the callers.
> 
> This bug has been present since tcheck() was introduced.
> 
> Link: https://bugs.launchpad.net/bugs/2107442
> Fixes: 8e03bd4e70b6 ("selftests/powerpc: Add TM tcheck helpers in C")
> Signed-off-by: Thibault Ferrante <thibault.ferrante@canonical.com>
> ---

Applied this patch on top of latest mainline and all the signal selftests are passing.


Please add below tags.

Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/all/364996ce-aba2-4213-8d20-7dd481b43fe6@linux.ibm.com/

With this Patch:


# make run_tests 
# timeout set to 0
# selftests: powerpc/signal: signal
ok 1 selftests: powerpc/signal: signal
# timeout set to 0
# selftests: powerpc/signal: signal_tm
ok 2 selftests: powerpc/signal: signal_tm
# timeout set to 0
# selftests: powerpc/signal: sigfuz
ok 3 selftests: powerpc/signal: sigfuz
# timeout set to 0
# selftests: powerpc/signal: sigreturn_vdso
ok 4 selftests: powerpc/signal: sigreturn_vdso
# timeout set to 0
# selftests: powerpc/signal: sig_sc_double_restart
ok 5 selftests: powerpc/signal: sig_sc_double_restart
# timeout set to 0
# selftests: powerpc/signal: sigreturn_kernel
ok 6 selftests: powerpc/signal: sigreturn_kernel
# timeout set to 0
# selftests: powerpc/signal: sigreturn_unaligned
ok 7 selftests: powerpc/signal: sigreturn_unaligned

Regards,
Venkat.



> tools/testing/selftests/powerpc/tm/tm.h | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/powerpc/tm/tm.h b/tools/testing/selftests/powerpc/tm/tm.h
> index c03c6e778876..6024ce4ba6ff 100644
> --- a/tools/testing/selftests/powerpc/tm/tm.h
> +++ b/tools/testing/selftests/powerpc/tm/tm.h
> @@ -105,8 +105,12 @@ static inline bool failure_is_nesting(void)
> static inline int tcheck(void)
> {
> long cr;
> - asm volatile ("tcheck 0" : "=r"(cr) : : "cr0");
> - return (cr >> 28) & 4;
> + asm volatile("tcheck 0;"
> +     "mfcr %0;"
> +     : "=r"(cr)
> +     :
> +     : "cr0");
> + return (cr >> 28) & 0xf;
> }
> 
> static inline bool tcheck_doomed(void)
> -- 
> 2.55.0
>