| Message ID | 20240814083428.3012-3-frediano.ziglio@cloud.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Support EFI multiboot loading using PE binary | expand |
On 14.08.2024 10:34, Frediano Ziglio wrote: > No reason to wait, if Xen image is loaded by EFI (not multiboot > EFI path) these are set in efi_arch_load_addr_check, but > not in the multiboot EFI code path. > This change makes the 2 EFI code paths more similar and allows > the usage of these variables if needed. It still remains a just-in-case change this way. It's init-only code, so the code size increase doesn't really matter, yet having such redundant code without a good explanation is at risk of being confusing down the road. Therefore - if this change is needed in a later patch in this series, please mention the intended use case here, or perhaps simply fold both patches. > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > --- > xen/arch/x86/boot/head.S | 5 +++++ > 1 file changed, 5 insertions(+) > --- > Changes since v1: > - Do not remove other hunk, used for BIOS; As indicated on the v1 thread: The writes simply write 0 in the BIOS case. It's the PVH case which needs them. With that I see two options: Move the existing code to ahead of __pvh_start's jump to trampoline_setup (my preference), or at least make sure that in the MB2 case we don't write the two variables a 2nd time (else raising the question of whether the same value is written, or why the value is okay to change.) > --- a/xen/arch/x86/boot/head.S > +++ b/xen/arch/x86/boot/head.S > @@ -240,6 +240,11 @@ __efi64_mb2_start: > jmp x86_32_switch > > .Lefi_multiboot2_proto: > + /* Save Xen image load base address for later use. */ > + lea __image_base__(%rip), %esi > + mov %rsi, xen_phys_start(%rip) > + mov %esi, trampoline_xen_phys_start(%rip) As iirc also indicated in reply to v1 already: The existing code you clone uses two 32-bit writes. What's the point of using a mix here? If the address was really above 4G, we'd have an issue anyway, wouldn't we? (Leaving aside that the LEA already truncates the value anyway.) Finally I'd like to recommend to avoid the use of %esi here. It gives the wrong impression of sym_esi() becoming usable, when in fact %esi is zeroed ... > /* Zero EFI SystemTable, EFI ImageHandle addresses and cmdline. */ > xor %esi,%esi ... immediately afterwards. Jan
diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S index 16830f636f..af598a60bf 100644 --- a/xen/arch/x86/boot/head.S +++ b/xen/arch/x86/boot/head.S @@ -240,6 +240,11 @@ __efi64_mb2_start: jmp x86_32_switch .Lefi_multiboot2_proto: + /* Save Xen image load base address for later use. */ + lea __image_base__(%rip), %esi + mov %rsi, xen_phys_start(%rip) + mov %esi, trampoline_xen_phys_start(%rip) + /* Zero EFI SystemTable, EFI ImageHandle addresses and cmdline. */ xor %esi,%esi xor %edi,%edi
No reason to wait, if Xen image is loaded by EFI (not multiboot EFI path) these are set in efi_arch_load_addr_check, but not in the multiboot EFI code path. This change makes the 2 EFI code paths more similar and allows the usage of these variables if needed. Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> --- xen/arch/x86/boot/head.S | 5 +++++ 1 file changed, 5 insertions(+) --- Changes since v1: - Do not remove other hunk, used for BIOS; - Slightly improved commit message.