https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119386
--- Comment #35 from Ard Biesheuvel <ardb at kernel dot org> --- (In reply to Alexander Monakov from comment #34) > We have -mcmodel=kernel already, which is incompatible with -fpic. > > Ard, where is -fpic in the kernel context coming from? Kernel's top-level > Makefile passes -fno-PIE, and arch/x86/Makefile passes -mcmodel=kernel. What > is the scenario your r14-811 patch was dealing with? These days, there is quite a lot of C code in Linux that executes before the kernel virtual mapping is even up, and this code (and everything that may be called by it) needs to be position independent. Currently, we rely on fragile hacks (RIP_REL_REF() for example) to try and ensure that this works, but it would be preferred if that code (or perhaps the entire kernel) could be built with -fPIC. There is some pushback to this, given that RIP-relative LEA is sometimes more expensive that a plain MOV (depending on the uarch) but not being able to use both -fPIC and -pg in the kernel was an impediment. (The indirect call opcode is longer, and does not honour -mnop-mcount, which is an issue for us)
