On Fri, Oct 4, 2024 at 11:06 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote: > > On 10/3/24 04:13, Ard Biesheuvel wrote: > > > >> That said, doing changes like changing "mov $sym" to "lea sym(%rip)" I > >> feel are a complete no-brainer and should be done regardless of any > >> other code generation issues. > > > > Yes, this is the primary reason I ended up looking into this in the > > first place. Earlier this year, we ended up having to introduce > > RIP_REL_REF() to emit those RIP-relative references explicitly, in > > order to prevent the C code that is called via the early 1:1 mapping > > from exploding. The amount of C code called in that manner has been > > growing steadily over time with the introduction of 5-level paging and > > SEV-SNP and TDX support, which need to play all kinds of tricks before > > the normal kernel mappings are created. > > > > movq $sym to leaq sym(%rip) which you said ought to be smaller (and in > reality appears to be the same size, 7 bytes) seems like a no-brainer > and can be treated as a code quality issue -- in other words, file bug > reports against gcc and clang. It is the kernel assembly source that should be converted to rip-relative form, gcc (and probably clang) have nothing with it. Uros.
