From ed28b16eab705071d28edaace47189c2eb3aa108 Mon Sep 17 00:00:00 2001 From: Thibault Ferrante Date: Mon, 7 Sep 2026 23:54:20 +0200 Subject: [PATCH] selftests/powerpc/tm: Fix tcheck() reading uninitialised CR value 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 Reported-by: Venkat Rao Bagalkote Tested-by: Venkat Rao Bagalkote Closes: https://lore.kernel.org/all/364996ce-aba2-4213-8d20-7dd481b43fe6@linux.ibm.com/ Signed-off-by: Madhavan Srinivasan Link: https://patch.msgid.link/20260907215420.1258678-1-thibault.ferrante@canonical.com --- 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)