On 04.07.2020 15:51, Jaromír Doleček wrote: > Le sam. 4 juil. 2020 à 15:30, Kamil Rytarowski <kamil%netbsd.org@localhost> a écrit : >>> Kamil - what's the difference in gcc between -Wframe-larger-than= and >>> -Wstack-size= ? >>> >> >> -Wstack-size doesn't exist? > > Sorry, meant -Wstack-usage= > It looks like WStack-usage is GCC specific (absent in Clang) and it includes alloca + vla. Both are not welcome in the kernel anyway so both should give in most cases the same result. >>> I see according to gcc documentation -Wframe-larger-than doesn't count >>> size for alloca() and variable-length arrays, which makes it much less >>> useful than -Wstack-usage. >>> >> >> It's not a problem. >> >> Whenever alloca or VLA is in use, it's already breaking the stack >> protector. There are a few exceptions registered in sys/conf/ssp.mk. >> >> We could add -Walloca -Wvla for USE_SSP=yes builds to catch quickly >> inappropriate usage (frequently violated by code optimizer). > > It's already not used in our kernel code, I checked and I found it > used only in some arch-specific stand/ code. So -Walloca should be > safe to turn on unconditionally, regardless of SSP. Unless the > compiler emits alloca() calls itself. > Sounds good. I'm for adding -Walloca and ideally -Wvla wherever possible in the kernel. > Jaromir >
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