Re: [PATCH hotfix 6.11] minmax: reduce egregious min/max macro expansion

Hi Lorenzo,

On 9/11/24 5:34 PM, Lorenzo Stoakes wrote:

Avoid nested min()/max() which results in egregious macro expansion.

This issue was introduced by commit 867046cc7027 ("minmax: relax check to
allow comparison between unsigned arguments and signed constants") [2].

Work has been done to address the issue of egregious min()/max() macro
expansion in commit 22f546873149 ("minmax: improve macro expansion and type
checking") and related, however it appears that some issues remain on more
tightly constrained systems.

Adjust a few known-bad cases of deeply nested macros to avoid doing so to
mitigate this. Porting the patch first proposed in [1] to Linus's tree.

Running an allmodconfig build using the methodology described in [2] we
observe a 35 MiB reduction in generated code.

The difference is much more significant prior to recent minmax fixes which
were not backported. As per [1] prior these the reduction is more like 200
MiB.

This resolves an issue with slackware 15.0 32-bit compilation as reported
by Richard Narron.

Presumably the min/max fixups would be difficult to backport, this patch
should be easier and fix's Richard's problem in 5.15.

[0]:https://lore.kernel.org/all/b97faef60ad24922b530241c5d7c933c@AcuMS.aculab.com/ (local)
[1]:https://lore.kernel.org/lkml/5882b96e-1287-4390-8174-3316d39038ef@lucifer.local/ (local)
[2]:https://lore.kernel.org/linux-mm/36aa2cad-1db1-4abf-8dd2-fb20484aabc3@lucifer.local/ (local)

Reported-by: Richard Narron <redacted>
Closes: https://lore.kernel.org/all/4a5321bd-b1f-1832-f0c-cea8694dc5aa@aaazen.com/ (local)
Fixes: 867046cc7027 ("minmax: relax check to allow comparison between unsigned arguments and signed constants")
Cc: stable@vger.kernel.org
Signed-off-by: Lorenzo Stoakes <redacted>

Thank you for your patch.

I must say that I'm not a fan of that this is patching 3 totally
unrelated files here in a single patch.

This is e.g. going to be a problem if we need to revert one of
the changes because of regressions...

So I would prefer this to be split into 3 patches.

One review comment for the atomisp bits inline / below.

drivers/staging/media/atomisp/pci/isp/kernels/s3a/s3a_1.0/ia_css_s3a.host.c

calls this with ia_css_3a_config.af_fir1_coef / .af_fir2_coef
as first argument those are of the ia_css_s0_15 type which is:

/* Signed fixed point value, 0 integer bits, 15 fractional bits */
typedef s32 ia_css_s0_15;

please replace the "short v" with "int v" 

I think that you can then also replace clamp_t() with clamp()

+	int fit_shift = sFRACTION_BITS_FITTING(a) - b;
+
+	v >>= sSHIFT;
+	v >>= fit_shift > 0 ? fit_shift : 0;
+
+	return clamp_t(int, v, sISP_VAL_MIN, sISP_VAL_MAX);
+}
+
+static inline unsigned int uDIGIT_FITTING(unsigned int v, int a, int b)
+{
+	int fit_shift = uFRACTION_BITS_FITTING(a) - b;
+
+	v >>= uSHIFT;
+	v >>= fit_shift > 0 ? fit_shift : 0;
+
+	return clamp_t(unsigned int, v, uISP_VAL_MIN, uISP_VAL_MAX);
+}

Regular clamp() should work here ? all parameters are already
unsigned ints.

Regards,

Hans