Instead of returning to the calling code in assembler that does nothing
more than perform an indirect call with the boot_params pointer in
register ESI/RSI, perform the jump directly from the EFI stub C code.
This will allow the asm entrypoint code to be dropped entirely in
subsequent patches.
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
drivers/firmware/efi/libstub/x86-stub.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 8d17cee8b98e1a63..095aaa8b0ee30fb9 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -769,9 +769,17 @@ static efi_status_t exit_boot(struct boot_params *boot_params, void *handle)
return EFI_SUCCESS;
}
+static void __noreturn enter_kernel(unsigned long kernel_addr,
+ struct boot_params *boot_params)
+{
+ /* enter decompressed kernel with boot_params pointer in RSI/ESI */
+ asm("jmp *%0"::"r"(kernel_addr), "S"(boot_params));
+
+ unreachable();
+}
+
/*
- * On success, we return the address of startup_32, which has potentially been
- * relocated by efi_relocate_kernel.
+ * On success, we jump to the relocated kernel directly and never return.
* On failure, we exit to the firmware via efi_exit instead of returning.
*/
asmlinkage unsigned long efi_main(efi_handle_t handle,
@@ -914,7 +922,11 @@ asmlinkage unsigned long efi_main(efi_handle_t handle,
goto fail;
}
- return bzimage_addr;
+ if (IS_ENABLED(CONFIG_X86_64))
+ /* add offset of startup_64() */
+ bzimage_addr += 0x200;
+
+ enter_kernel(bzimage_addr, boot_params);
fail:
efi_err("efi_main() failed!\n");
--
2.39.2
