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Add this flag explicitly. >>>> +ifdef CONFIG_CC_IS_CLANG >>>> +DEBUG_CFLAGS    += -grecord-gcc-switches >>>> +endif >>>> + > > Yes, gcc defaults to -grecord-gcc-switches. Clang doesn't. Could you know why? dwarf size concern? > >>> This adds ~5MB/1% to vmlinux of an x86_64 defconfig built with clang. >>> Do we >>> want to add additional guards for CONFIG_DEBUG_INFO_BTF, so that we >>> don't have >>> to pay that cost if that config is not set? >> >> Since this patch is mostly motivated to detect whether the kernel is >> built with clang lto or not. Let me add the flag only if lto is >> enabled. My measurement shows 0.5% increase to thinlto-vmlinux. >> The smaller percentage is due to larger .debug_info section >> (almost double) for thinlto vs. no lto. >> >> ifdef CONFIG_LTO_CLANG >> DEBUG_CFLAGS   += -grecord-gcc-switches >> endif >> >> This will make pahole with any clang built kernels, lto or non-lto. > > I share the same concern about sizes. Can't pahole know it is clang LTO > via other means? If pahole just needs to know the one-bit information > (clang LTO vs not), having every compile option seems unnecessary.... This is v2 of the patch https://lore.kernel.org/bpf/20210331001623.2778934-1-yhs@fb.com/ The flag will be guarded with CONFIG_LTO_CLANG. As mentioned in commit message of v2, the alternative is to go through every cu to find out whether DW_FORM_ref_addr is used or not. In other words, check every possible cross-cu references to find whether cross-cu reference actually happens or not. This is quite heavy for pahole... What we really want to know is whether cross-cu reference happens or not? If there is an easy way to get it, that will be great. > >> If the maintainer wants further restriction with CONFIG_DEBUG_INFO_BTF, >> I can do that in another revision. >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Clang Built Linux" group. >> To unsubscribe from this group and stop receiving emails from it, send >> an email to clang-built-linux+unsubscribe@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/clang-built-linux/0b8d17be-e015-83c3-88d8-7c218cd01536@fb.com >> .