cast to unsigned char before toupper in cache size parser

[soma0212]

toupper() in cache_size_parser gets a plain char, which is signed on the ARM/Android targets this file builds for:

• the argument is the first non-digit byte of the sysfs cache-size value (/sys/.../cache/indexN/size), so any byte >= 0x80 reaches toupper as a negative int
• C11 7.4p1 requires the argument to be representable as unsigned char or equal to EOF; bionic and musl index their ctype table directly with it, so a negative value is an out-of-bounds read
• cast to unsigned char, the standard guard for ctype on possibly-signed input

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[fbarchard]

makes sense. its good there is a comment above showing (e.g. "2048K", "1M")
for context. Makes me think the default
uint32_t multiplier = 1024;
should really be '1' and check for 'K' the same way.

or just expect it to be upper case. when I check my linux workstation it says
more /sys/devices/system/cpu/cpu0/cache/index0/size
32K
pixel2 android device is
adb shell more /sys/devices/system/cpu/cpu0/cache/index0/size
32K

[soma0212]

Right, the generic cacheinfo driver formats this value as "%uK" (size_show in drivers/base/cacheinfo.c), so on mainline kernels the suffix is always present and always uppercase, which lines up with what you're seeing on both your boxes. That means the KB default and the toupper only matter for vendor kernels that stray from that, and treating a bare number as KB has been this parser's behavior all along. I kept this PR to just the cast so it fixes the UB without changing behavior on any input, but happy to switch to multiplier = 1 with an explicit 'K' check in a follow-up if you'd prefer that shape.