diff mbox series

[v4,3/6] x86/boot: Reuse code to relocate trampoline

Message ID 20241014085332.3254546-4-frediano.ziglio@cloud.com (mailing list archive)
State Superseded
Headers show
Series Reuse 32 bit C code more safely | expand

Commit Message

Frediano Ziglio Oct. 14, 2024, 8:53 a.m. UTC 
Move code from efi-boot.h to a separate, new, reloc-trampoline.c file.
Reuse this new code, compiling it for 32bit as well, to replace assembly
code in head.S doing the same thing.

Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
Changes since v3:
- fixed a typo in comment;
- added Reviewed-by.
---
 xen/arch/x86/boot/Makefile           | 12 ++++++----
 xen/arch/x86/boot/build32.lds.S      |  5 ++++
 xen/arch/x86/boot/head.S             | 23 +-----------------
 xen/arch/x86/boot/reloc-trampoline.c | 36 ++++++++++++++++++++++++++++
 xen/arch/x86/efi/efi-boot.h          | 15 ++----------
 5 files changed, 52 insertions(+), 39 deletions(-)
 create mode 100644 xen/arch/x86/boot/reloc-trampoline.c

Comments

Anthony PERARD Oct. 15, 2024, 3:03 p.m. UTC | #1 
On Mon, Oct 14, 2024 at 09:53:29AM +0100, Frediano Ziglio wrote:
> diff --git a/xen/arch/x86/boot/Makefile b/xen/arch/x86/boot/Makefile
> index 23ad274c89..ca258a9729 100644
> --- a/xen/arch/x86/boot/Makefile
> +++ b/xen/arch/x86/boot/Makefile
> @@ -1,12 +1,16 @@
>  obj-bin-y += head.o
>  obj-bin-y += built_in_32.o
> +obj-bin-y += $(obj64)

Could you move this so $(obj64) is fully set when added to $(obj-bin-y)?
There's no garanties that this is going to keep working. We already have
"obj-y :=", so it is possible we will have "obj-bin-y :=" one day. (Or
that we get rid of $(obj-bin-y) because it becomes unnecessary.)

>  obj32 := cmdline.32.o
>  obj32 += reloc.32.o
> +obj32 += reloc-trampoline.32.o
>  
> -nocov-y   += $(obj32)
> -noubsan-y += $(obj32)
> -targets   += $(obj32)
> +obj64 := reloc-trampoline.o
> +
> +nocov-y   += $(obj32) $(obj64)
> +noubsan-y += $(obj32) $(obj64)
> +targets   += $(obj32) $(obj64)

Technically, the change to $(targets) isn't necessary, $(obj-bin-y)
should already be added to it.

Cheers,
diff mbox series

Patch

diff --git a/xen/arch/x86/boot/Makefile b/xen/arch/x86/boot/Makefile
index 23ad274c89..ca258a9729 100644
--- a/xen/arch/x86/boot/Makefile
+++ b/xen/arch/x86/boot/Makefile
@@ -1,12 +1,16 @@ 
 obj-bin-y += head.o
 obj-bin-y += built_in_32.o
+obj-bin-y += $(obj64)
 
 obj32 := cmdline.32.o
 obj32 += reloc.32.o
+obj32 += reloc-trampoline.32.o
 
-nocov-y   += $(obj32)
-noubsan-y += $(obj32)
-targets   += $(obj32)
+obj64 := reloc-trampoline.o
+
+nocov-y   += $(obj32) $(obj64)
+noubsan-y += $(obj32) $(obj64)
+targets   += $(obj32) $(obj64)
 
 obj32 := $(addprefix $(obj)/,$(obj32))
 
@@ -50,7 +54,7 @@  $(obj)/built_in_32.S: $(obj)/built_in_32.other.bin $(obj)/built_in_32.final.bin
 		--bin1 $(obj)/built_in_32.other.bin \
 		--bin2 $(obj)/built_in_32.final.bin \
 		--map $(obj)/built_in_32.final.map \
-		--exports cmdline_parse_early,reloc \
+		--exports cmdline_parse_early,reloc,reloc_trampoline32 \
 		--output $@
 
 clean-files := built_in_32.*.bin built_in_32.*.map build32.*.lds
diff --git a/xen/arch/x86/boot/build32.lds.S b/xen/arch/x86/boot/build32.lds.S
index 50c167aef0..1110880ad4 100644
--- a/xen/arch/x86/boot/build32.lds.S
+++ b/xen/arch/x86/boot/build32.lds.S
@@ -41,6 +41,11 @@  SECTIONS
          * Potentially they should be all variables. */
         DECLARE_IMPORT(__base_relocs_start);
         DECLARE_IMPORT(__base_relocs_end);
+        DECLARE_IMPORT(__trampoline_rel_start);
+        DECLARE_IMPORT(__trampoline_rel_stop);
+        DECLARE_IMPORT(__trampoline_seg_start);
+        DECLARE_IMPORT(__trampoline_seg_stop);
+        DECLARE_IMPORT(trampoline_phys);
         . = . + GAP;
         *(.text)
         *(.text.*)
diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index e0776e3896..ade2c5c43d 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -706,28 +706,7 @@  trampoline_setup:
         mov     %edx, sym_offs(l1_bootmap)(%esi, %ecx, 8)
 
         /* Apply relocations to bootstrap trampoline. */
-        mov     sym_esi(trampoline_phys), %edx
-        lea     sym_esi(__trampoline_rel_start), %edi
-        lea     sym_esi(__trampoline_rel_stop), %ecx
-1:
-        mov     (%edi), %eax
-        add     %edx, (%edi, %eax)
-        add     $4,%edi
-
-        cmp     %ecx, %edi
-        jb      1b
-
-        /* Patch in the trampoline segment. */
-        shr     $4,%edx
-        lea     sym_esi(__trampoline_seg_start), %edi
-        lea     sym_esi(__trampoline_seg_stop), %ecx
-1:
-        mov     (%edi), %eax
-        mov     %dx, (%edi, %eax)
-        add     $4,%edi
-
-        cmp     %ecx, %edi
-        jb      1b
+        call    reloc_trampoline32
 
         /* Do not parse command line on EFI platform here. */
         cmpb    $0, sym_esi(efi_platform)
diff --git a/xen/arch/x86/boot/reloc-trampoline.c b/xen/arch/x86/boot/reloc-trampoline.c
new file mode 100644
index 0000000000..0a74c1e75a
--- /dev/null
+++ b/xen/arch/x86/boot/reloc-trampoline.c
@@ -0,0 +1,36 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/compiler.h>
+#include <xen/stdint.h>
+#include <asm/trampoline.h>
+
+extern const int32_t __trampoline_rel_start[], __trampoline_rel_stop[];
+extern const int32_t __trampoline_seg_start[], __trampoline_seg_stop[];
+
+#if defined(__i386__)
+void reloc_trampoline32(void)
+#elif defined (__x86_64__)
+void reloc_trampoline64(void)
+#else
+#error Unknown architecture
+#endif
+{
+    unsigned long phys = trampoline_phys;
+    const int32_t *trampoline_ptr;
+
+    /*
+     * Apply relocations to trampoline.
+     *
+     * This modifies the trampoline in place within Xen, so that it will
+     * operate correctly when copied into place.
+     */
+    for ( trampoline_ptr = __trampoline_rel_start;
+          trampoline_ptr < __trampoline_rel_stop;
+          ++trampoline_ptr )
+        *(uint32_t *)(*trampoline_ptr + (long)trampoline_ptr) += phys;
+
+    for ( trampoline_ptr = __trampoline_seg_start;
+          trampoline_ptr < __trampoline_seg_stop;
+          ++trampoline_ptr )
+        *(uint16_t *)(*trampoline_ptr + (long)trampoline_ptr) = phys >> 4;
+}
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 94f3443364..1acceec471 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -103,27 +103,16 @@  static void __init efi_arch_relocate_image(unsigned long delta)
     }
 }
 
-extern const int32_t __trampoline_rel_start[], __trampoline_rel_stop[];
-extern const int32_t __trampoline_seg_start[], __trampoline_seg_stop[];
+void reloc_trampoline64(void);
 
 static void __init relocate_trampoline(unsigned long phys)
 {
-    const int32_t *trampoline_ptr;
-
     trampoline_phys = phys;
 
     if ( !efi_enabled(EFI_LOADER) )
         return;
 
-    /* Apply relocations to trampoline. */
-    for ( trampoline_ptr = __trampoline_rel_start;
-          trampoline_ptr < __trampoline_rel_stop;
-          ++trampoline_ptr )
-        *(u32 *)(*trampoline_ptr + (long)trampoline_ptr) += phys;
-    for ( trampoline_ptr = __trampoline_seg_start;
-          trampoline_ptr < __trampoline_seg_stop;
-          ++trampoline_ptr )
-        *(u16 *)(*trampoline_ptr + (long)trampoline_ptr) = phys >> 4;
+    reloc_trampoline64();
 }
 
 static void __init place_string(u32 *addr, const char *s)