[PATCH v7 2/4] x86/efi: discard multiboot and PVH support for PE binary

[Frediano Ziglio <freddy77@xxxxxxxxx>]

From: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Multiboot and PVH booting are not supported for PE, hence discards them
in the linker script when doing a PE build.

That removes some relocations that otherwise appear due to the usage of the
start and __efi64_mb2_start symbols in the multiboot2 header.

Section discarding is not done updating DISCARD_SECTIONS definition as the
change is specific for x86.

No functional change intended.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
---
Changes since v1:
- improve commit message;
- change section orders to avoid changing code order in final executable;
- merge 2 commits;
- removed deprecated documentation section.

Changes since v2:
- Update commit message, join 2 sentences together.

Changes since v3:
- Added Acked-by.

Changes since v4:
- more clear subject;
- removed more code/data from EFI output;
- removed Acked-by.

Changes since v5:
- simplify section exclusion using more wildcard;
- exclude more multiboot functions.
---
 docs/hypervisor-guide/x86/how-xen-boots.rst | 6 ------
 xen/arch/x86/boot/head.S                    | 8 ++++----
 xen/arch/x86/xen.lds.S                      | 7 +++++++
 xen/tools/combine_two_binaries.py           | 2 +-
 4 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/docs/hypervisor-guide/x86/how-xen-boots.rst 
b/docs/hypervisor-guide/x86/how-xen-boots.rst
index 8b3229005c..b6d852050a 100644
--- a/docs/hypervisor-guide/x86/how-xen-boots.rst
+++ b/docs/hypervisor-guide/x86/how-xen-boots.rst
@@ -82,12 +82,6 @@ When a PEI-capable toolchain is found, the objects are 
linked together and a
 PE32+ binary is created.  It can be run directly from the EFI shell, and has
 ``efi_start`` as its entry symbol.
 
-.. note::
-
-   xen.efi does contain all MB1/MB2/PVH tags included in the rest of the
-   build.  However, entry via anything other than the EFI64 protocol is
-   unsupported, and won't work.
-
 
 Boot
 ----
diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 68b963ce6f..981f262b5e 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -126,7 +126,7 @@ multiboot2_header:
         .size multiboot2_header, . - multiboot2_header
         .type multiboot2_header, @object
 
-        .section .init.rodata, "a", @progbits
+        .section .init.rodata.multiboot, "a", @progbits
 
 .Lbad_cpu_msg: .asciz "ERR: Not a 64-bit CPU!"
 .Lbad_ldr_msg: .asciz "ERR: Not a Multiboot bootloader!"
@@ -137,8 +137,7 @@ multiboot2_header:
 .Lno_nx_msg:   .asciz "ERR: Not an NX-capable CPU!"
 #endif
 
-        .section .init.data, "aw", @progbits
-        .subsection 1 /* Put data here after the page tables (in x86_64.S). */
+        .section .init.data.multiboot, "aw", @progbits
         .align 4
 
         .word   0
@@ -154,7 +153,7 @@ vga_text_buffer:
 efi_platform:
         .byte   0
 
-        .section .init.text, "ax", @progbits
+        .section .init.multiboot, "ax", @progbits
 
 early_error: /* Here to improve the disassembly. */
 
@@ -712,6 +711,7 @@ trampoline_setup:
         /* Jump into the relocated trampoline. */
         lret
 
+        .section .init.text, "ax", @progbits
 ENTRY(trampoline_start)
 #include "trampoline.S"
 ENTRY(trampoline_end)
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 8e63cf5bc2..4ed1d2bec1 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -57,6 +57,10 @@ SECTIONS
   __image_base__ = .;
 #else
   . = __image_base__;
+  /DISCARD/ : {
+    *(.text.header)
+    *(.init.*multiboot)
+  }
 #endif
 
 #if 0
@@ -195,6 +199,7 @@ SECTIONS
   DECL_SECTION(.init.text) {
 #endif
        _sinittext = .;
+       *(.init.multiboot)
        *(.init.text)
        *(.text.startup)
        _einittext = .;
@@ -220,6 +225,7 @@ SECTIONS
        *(.init.rodata.cf_clobber)
        __initdata_cf_clobber_end = .;
 
+       *(.init.rodata.multiboot)
        *(.init.rodata)
        *(.init.rodata.*)
 
@@ -234,6 +240,7 @@ SECTIONS
        *(.initcall1.init)
        __initcall_end = .;
 
+       *(.init.data.multiboot)
        *(.init.data)
        *(.init.data.rel)
        *(.init.data.rel.*)
diff --git a/xen/tools/combine_two_binaries.py 
b/xen/tools/combine_two_binaries.py
index 581e57cbc0..5f0433dcad 100755
--- a/xen/tools/combine_two_binaries.py
+++ b/xen/tools/combine_two_binaries.py
@@ -33,7 +33,7 @@ parser.add_argument('--map', dest='mapfile',
 parser.add_argument('--exports', dest='exports',
                     help='Symbols to export')
 parser.add_argument('--section-header', dest='section_header',
-                    default='.section .init.text, "ax", @progbits',
+                    default='.section .init.multiboot, "ax", @progbits',
                     help='Section header declaration')
 parser.add_argument('-v', '--verbose',
                     action='store_true')
-- 
2.43.0