[PATCH] clk: tenstorrent: Assign .num before accessing .hws

[Aamir Ahmed]

Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
__counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS)
about the number of elements in .hws[], so that it can warn when .hws[]
is accessed out of bounds. As noted in that change, the __counted_by
member must be initialized with the number of elements before the first
array access happens, otherwise there will be a warning from each access
prior to the initialization because the number of elements is zero.
This occurs in atlantis_prcm_clocks_register() due to .num being
assigned only after every clock has been stored in .hws[]. With
CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC
15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report
during probe, and with CONFIG_UBSAN_TRAP the first store traps so the
clock provider never registers.

Move the .num initialization to right after the allocation.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 23c8ebc95284 ("clk: tenstorrent: Add Atlantis clock controller driver")
Assisted-by: LLM
Signed-off-by: Aamir Ahmed <elb12345@xxxxxxxxxxxxx>
---
Found while auditing the remaining clk_hw_onecell_data users that assign
.num only after touching .hws[], following the fixes already merged for
clk-s2mps11 (3e14c7207a97), exynos-clkout (cf33f0b7df13) and
clk-raspberrypi (6dc445c19050). The audit, the fix and this changelog
were drafted with an LLM assistant and reviewed by hand.

Compile-tested only (W=1, no warnings) on x86_64 with GCC 13.3, via
COMPILE_TEST with CONFIG_TENSTORRENT_ATLANTIS_PRCM=m. GCC 13.3 does not
implement __counted_by (CC_HAS_COUNTED_BY needs GCC 15.1+ or Clang
20.1+), so the build only confirms that the change compiles; the
sanitizer path was not exercised. I do not have the hardware, so this is
not runtime-tested and no UBSAN report was captured.

Based on v7.3-rc1.

 drivers/clk/tenstorrent/atlantis-prcm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/tenstorrent/atlantis-prcm.c b/drivers/clk/tenstorrent/atlantis-prcm.c
index 6d4386eeb7d..a68534a295c 100644
--- a/drivers/clk/tenstorrent/atlantis-prcm.c
+++ b/drivers/clk/tenstorrent/atlantis-prcm.c
@@ -796,6 +796,8 @@ static int atlantis_prcm_clocks_register(struct device *dev,
 	if (!clk_data)
 		return -ENOMEM;
 
+	clk_data->num = num_clks;
+
 	for (i = 0; i < data->num; i++) {
 		struct clk_hw *hw = data->hws[i];
 		struct atlantis_clk_common *common =
@@ -809,8 +811,6 @@ static int atlantis_prcm_clocks_register(struct device *dev,
 		clk_data->hws[common->clkid] = hw;
 	}
 
-	clk_data->num = num_clks;
-
 	return devm_of_clk_add_hw_provider(dev, of_clk_hw_onecell_get, clk_data);
 }
 

base-commit: 654ae5d73c05bd2943d65636ce6cd0aa46e62f18
-- 
2.53.0.windows.1