[Xen-devel] [PATCH v2] xen/x86: fix linker script to work with lld

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

lld (the llvm linker) has some issues with Xen linker script. It
doesn't understand '||' in assert expressions:

ld    -melf_x86_64_fbsd  -T xen.lds -N prelink.o --build-id=sha1 \
    /root/src/xen/xen/common/symbols-dummy.o -o /root/src/xen/xen/.xen-syms.0
ld: error: xen.lds:260: malformed number: |
>>> ASSERT(__image_base__ > (((((((((261 >> 8) * 0xffff000000000000) | (261 << 
>>> 39))) + ((1 << 39) / 2)) + (64 << 30)) + (1 << 30)) + (1 << 30))) ||
>>>                                                                             
>>>                                                                   ^

And doesn't work properly with the 'DEFINED(foo) ? foo : ...'
expression:

ld    -melf_x86_64_fbsd  -T xen.lds -N prelink.o --build-id=sha1 \
    /root/src/xen/xen/common/symbols-dummy.o -o /root/src/xen/xen/.xen-syms.0
ld: error: xen.lds:233: symbol not found: efi

Fix the first issue by using '|' instead of '||', and the second one
by declaring the efi symbol as a weak symbol.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
Changes since v1:
 - Export efi as a weak symbol in order to remove the DEFINED
   conditional in the linker script.
 - Add a define for setting the weak attribute and replace existing
   users.
---
 xen/arch/x86/xen.lds.S              | 4 +---
 xen/include/xen/compiler.h          | 2 ++
 xen/include/xen/efi.h               | 2 +-
 xen/include/xen/livepatch_payload.h | 4 ++--
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 70afedd31d..9fa40a6d48 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -304,8 +304,6 @@ SECTIONS
   } :text
 #endif
 
-  efi = DEFINED(efi) ? efi : .;
-
   /* Sections to be discarded */
   /DISCARD/ : {
        *(.exit.text)
@@ -331,7 +329,7 @@ SECTIONS
   .comment 0 : { *(.comment) }
 }
 
-ASSERT(__image_base__ > XEN_VIRT_START ||
+ASSERT(__image_base__ > XEN_VIRT_START |
        __2M_rwdata_end <= XEN_VIRT_END - NR_CPUS * PAGE_SIZE,
        "Xen image overlaps stubs area")
 
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index a7e05681c9..001f589655 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -18,6 +18,8 @@
 
 #define __packed      __attribute__((__packed__))
 
+#define __weak        __attribute__((weak))
+
 #if (!defined(__clang__) && (__GNUC__ == 4) && (__GNUC_MINOR__ < 5))
 #define unreachable() do {} while (1)
 #else
diff --git a/xen/include/xen/efi.h b/xen/include/xen/efi.h
index 44b7d3ec3a..5678df72f9 100644
--- a/xen/include/xen/efi.h
+++ b/xen/include/xen/efi.h
@@ -21,7 +21,7 @@ struct efi {
     unsigned long smbios3;      /* SMBIOS v3 table */
 };
 
-extern struct efi efi;
+extern struct efi __weak efi;
 
 #ifndef __ASSEMBLY__
 
diff --git a/xen/include/xen/livepatch_payload.h 
b/xen/include/xen/livepatch_payload.h
index 8f38cc2c60..4a1a96d054 100644
--- a/xen/include/xen/livepatch_payload.h
+++ b/xen/include/xen/livepatch_payload.h
@@ -24,7 +24,7 @@ typedef void livepatch_unloadcall_t(void);
  * executed in series by the livepatch infrastructure at patch load time.
  */
 #define LIVEPATCH_LOAD_HOOK(_fn) \
-    livepatch_loadcall_t *__attribute__((weak)) \
+    livepatch_loadcall_t *__weak \
         const livepatch_load_data_##_fn __section(".livepatch.hooks.load") = 
_fn;
 
 /*
@@ -33,7 +33,7 @@ typedef void livepatch_unloadcall_t(void);
  * Same as LOAD hook with s/load/unload/
  */
 #define LIVEPATCH_UNLOAD_HOOK(_fn) \
-     livepatch_unloadcall_t *__attribute__((weak)) \
+     livepatch_unloadcall_t *__weak \
         const livepatch_unload_data_##_fn __section(".livepatch.hooks.unload") 
= _fn;
 
 #endif /* __XEN_LIVEPATCH_PAYLOAD_H__ */
-- 
2.17.1


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