[Xen-devel] [PATCH 3/4] xen: introduce __symbol

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Introduce a macro, __symbol, which is a simple wrapper around RELOC_HIDE
to be used everywhere symbols such as _stext and _etext are used in the
code.

RELOC_HIDE is needed when accessing symbols such as _stext and _etext
because the C standard forbids comparisons between pointers pointing to
different objects. _stext, _etext, etc. are all pointers to different
objects from ANCI C point of view.

To work around potential C compiler issues (which have actually
been found, see the comment on top of RELOC_HIDE in Linux), and to help
with certifications, let's introduce some syntactic sugar to be used in
following patches.

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
---
 xen/include/asm-arm/mm.h   | 6 ++++++
 xen/include/asm-x86/page.h | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index 940b74b..02ce05a 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -284,6 +284,12 @@ static inline uint64_t gvirt_to_maddr(vaddr_t va, paddr_t 
*pa,
 #define __mfn_to_virt(mfn) (maddr_to_virt((paddr_t)(mfn) << PAGE_SHIFT))
 
 /*
+ * Use RELOC_HIDE with symbols such as _stext and _etext to avoid errors
+ * on comparing pointers to different objects
+ */
+#define __symbol(x)         ((char *)RELOC_HIDE((unsigned long)(x), 0))
+
+/*
  * We define non-underscored wrappers for above conversion functions.
  * These are overriden in various source files while underscored version
  * remain intact.
diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index c1e9293..3f1592b 100644
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -274,6 +274,12 @@ void copy_page_sse2(void *, const void *);
 #define vmap_to_mfn(va)     _mfn(l1e_get_pfn(*virt_to_xen_l1e((unsigned 
long)(va))))
 #define vmap_to_page(va)    mfn_to_page(vmap_to_mfn(va))
 
+/*
+ * Use RELOC_HIDE with symbols such as _stext and _etext to avoid errors
+ * on comparing pointers to different objects
+ */
+#define __symbol(x)         ((char *)RELOC_HIDE((unsigned long)(x), 0))
+
 #endif /* !defined(__ASSEMBLY__) */
 
 /* Where to find each level of the linear mapping */
-- 
1.9.1


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