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selftests/powerpc/tm: Fix tcheck() reading uninitialised CR value

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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: 8e03bd4e70 ("selftests/powerpc: Add TM tcheck helpers in C")
Signed-off-by: Thibault Ferrante <thibault.ferrante@canonical.com>
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/
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260907215420.1258678-1-thibault.ferrante@canonical.com
This commit is contained in:
Thibault Ferrante 2026-09-07 23:54:20 +02:00 committed by Madhavan Srinivasan
parent ef17515a8e
commit ed28b16eab
1 changed files with 6 additions and 2 deletions
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8
tools/testing/selftests/powerpc/tm/tm.h
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@ -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)