arm64 ld.lld: warning: stack frame size (2256) exceeds limit (2048) in function 'wlc_phy_txpwr_srom_read_ppr_nphy'

[emojifreak]

All built-in configuration similar to #1550 gives a build warning at the final stage

  LTO     vmlinux.o
ld.lld: warning: stack frame size (2256) exceeds limit (2048) in function 'wlc_phy_txpwr_srom_read_ppr_nphy'

This probably causes build failure with CONFIG_WERROR=y. .config and a reproducing script are attached. It is unclear to me why it is not caught by clang.
config.txt.gz
clang-build-arch30.sh.gz

[nickdesaulniers]

If you run this on the vmlinux, it might be able to help us spot if there's a large stack allocation, or lots of little ones.

[emojifreak]

Thank you. I will try to provide further info. by https://github.com/ClangBuiltLinux/frame-larger-than

[emojifreak]

@nickdesaulniers It didn't work as

ryutaroh@bookworm-amd64:/var/tmp/tmp30/arm64/linux-5.16-rc6$ python3 /var/tmp/frame_larger_than.py drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.\
o wlc_phy_txpwr_srom_read_ppr_nphy
failed to parse elf: Magic number does not match
ryutaroh@bookworm-amd64:/var/tmp/tmp30/arm64/linux-5.16-rc6$ file drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.o 
drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.o: LLVM IR bitcode

[nickdesaulniers]

@emojifreak right, you're running the script on a .o file which actually is LLVM bitcode (should be a .bc file). Since it's not an ELF object, an ELF parser will fail to find the ELF magic number at the expected location of an ELF object header. That's why I suggested running it on vmlinux, which will take longer, but is a fully linked ELF object.

[emojifreak]

Thanks. The configuration causes this warning fails before making vmlinux and I don't have vmlinux, so I will seek a configuration building vmlinux with this warning... I will report it when I get a useful additional info.

[nickdesaulniers]

Does ./scripts/config -d WERROR allow you to complete the build?

[emojifreak]

No, so far. Because I can observe this symptom only with #1550. I need to reproduce this without seeing #1550 so that I can have vmlinux...