> On Dec 28, 2019, at 2:35 PM, Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > On Sat, Dec 28, 2019 at 01:29:00PM +0800, Andy Lutomirski wrote: >> >>> * The stack must be 16-byte aligned >> >> Nope. The asm needs to do this for runtime services. The kernel runs with 8-byte stack alignment. >> > 32-bit code is actually only 4-byte aligned in the kernel proper, right? Right. By “8” I meant “long”. Sorry. > > Currently, only native 64-bit calls always respect the 16-byte alignment > requirement, by aligning explicitly in the asm stubs, or after the > cleanup patches, via the efi bootloader running with 16-byte stack > alignment. > > I think mixed mode might actually be aligned via the asm stub in the > kernel proper, though it doesn't look like it is in the bootloader > portion. The underlying problem is that gcc doesn’t give us a way to do CALL from asm while preserving more than a single word of alignment. This forces us to compile the kernel proper with reduced alignment. (Also, the generated code is better with reduced alignment.)
