diff mbox series

[v2,03/20] x86: decompressor: Call trampoline as a normal function

Message ID 20230508070330.582131-4-ardb@kernel.org
State New
Headers
Series efi/x86: Avoid bare metal decompressor during EFI boot |

Commit Message

Ard Biesheuvel May 8, 2023, 7:03 a.m. UTC 
  Move the long return to switch to 32-bit mode into the trampoline code
so we can call it as an ordinary function. This will allow us to call it
directly from C code in a subsequent patch.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/boot/compressed/head_64.S | 25 +++++++++-----------
 arch/x86/boot/compressed/pgtable.h |  2 +-
 2 files changed, 12 insertions(+), 15 deletions(-)

Comments

Kirill A. Shutemov May 15, 2023, 1:59 p.m. UTC | #1 
On Mon, May 08, 2023 at 09:03:13AM +0200, Ard Biesheuvel wrote:
> Move the long return to switch to 32-bit mode into the trampoline code
> so we can call it as an ordinary function. This will allow us to call it
> directly from C code in a subsequent patch.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
diff mbox series

Patch

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 59340e533dff8369..81b53b576cdd05ae 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -457,18 +457,9 @@  SYM_CODE_START(startup_64)
 	/* Save the trampoline address in RCX */
 	movq	%rax, %rcx
 
-	/*
-	 * Load the address of trampoline_return() into RDI.
-	 * It will be used by the trampoline to return to the main code.
-	 */
-	leaq	trampoline_return(%rip), %rdi
-
-	/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
-	pushq	$__KERNEL32_CS
 	leaq	TRAMPOLINE_32BIT_CODE_OFFSET(%rax), %rax
-	pushq	%rax
-	lretq
-trampoline_return:
+	call	*%rax
+
 	/* Restore the stack, the 32-bit trampoline uses its own stack */
 	leaq	rva(boot_stack_end)(%rbx), %rsp
 
@@ -566,16 +557,22 @@  SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
 	jmp	*%rax
 SYM_FUNC_END(.Lrelocated)
 
-	.code32
 /*
  * This is the 32-bit trampoline that will be copied over to low memory.
  *
- * RDI contains the return address (might be above 4G).
  * ECX contains the base address of the trampoline memory.
  * Non zero RDX means trampoline needs to enable 5-level paging.
  */
 SYM_CODE_START(trampoline_32bit_src)
-	/* Set up data and stack segments */
+	popq	%rdi
+	/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
+	pushq	$__KERNEL32_CS
+	leaq	0f(%rip), %rax
+	pushq	%rax
+	lretq
+
+	.code32
+0:	/* Set up data and stack segments */
 	movl	$__KERNEL_DS, %eax
 	movl	%eax, %ds
 	movl	%eax, %ss
diff --git a/arch/x86/boot/compressed/pgtable.h b/arch/x86/boot/compressed/pgtable.h
index cc9b2529a08634b4..91dbb99203fbce2d 100644
--- a/arch/x86/boot/compressed/pgtable.h
+++ b/arch/x86/boot/compressed/pgtable.h
@@ -6,7 +6,7 @@ 
 #define TRAMPOLINE_32BIT_PGTABLE_OFFSET	0
 
 #define TRAMPOLINE_32BIT_CODE_OFFSET	PAGE_SIZE
-#define TRAMPOLINE_32BIT_CODE_SIZE	0x80
+#define TRAMPOLINE_32BIT_CODE_SIZE	0xA0
 
 #define TRAMPOLINE_32BIT_STACK_END	TRAMPOLINE_32BIT_SIZE