Re: [PATCH] spi: rockchip: avoid objtool warning
From: Arnd Bergmann
Date: Fri Feb 26 2021 - 04:51:06 EST
On Fri, Feb 26, 2021 at 9:16 AM 'Pratyush Yadav' via Clang Built Linux
<clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
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Hi,
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On 25/02/21 01:55PM, Arnd Bergmann wrote:
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> From: Arnd Bergmann <arnd@xxxxxxxx>
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> Building this file with clang leads to a an unreachable code path
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> causing a warning from objtool:
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> drivers/spi/spi-rockchip.o: warning: objtool: rockchip_spi_transfer_one()+0x2e0: sibling call from callable instruction with modified stack frame
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> Use BUG() instead of unreachable() to avoid the undefined behavior
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> if it does happen.
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> Fixes: 65498c6ae241 ("spi: rockchip: support 4bit words")
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> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
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> ---
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> drivers/spi/spi-rockchip.c | 2 +-
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> 1 file changed, 1 insertion(+), 1 deletion(-)
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> diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
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> index 936ef54e0903..972beac1169a 100644
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> --- a/drivers/spi/spi-rockchip.c
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> +++ b/drivers/spi/spi-rockchip.c
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> @@ -521,7 +521,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
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> * ctlr->bits_per_word_mask, so this shouldn't
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> * happen
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> */
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> - unreachable();
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> + BUG();
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checkpatch says:
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Avoid crashing the kernel - try using WARN_ON & recovery code rather
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than BUG() or BUG_ON()
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Which makes sense to me. This is not something bad enough to justify
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crashing the kernel.
I thought about rewriting it more thoroughly when I wrote the patch, but
couldn't come up with a good alternative, so I did the simplest change
in this direction, replacing the silent crash with a loud one.
Should we just dev_warn() and return instead, hoping that it won't do
more harm?
The backtrace from WARN_ON() probably doesn't help here.
Arnd