[PATCH v3 2/8] common: assembly entry point type/size annotations

[Jan Beulich <jbeulich@xxxxxxxx>]

Recent gas versions generate minimalistic Dwarf debug info for items
annotated as functions and having their sizes specified [1]. Furthermore
generating live patches wants items properly annotated. "Borrow" Arm's
END() and (remotely) derive other annotation infrastructure from
Linux'es, for all architectures to use.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

[1] 
https://sourceware.org/git?p=binutils-gdb.git;a=commitdiff;h=591cc9fbbfd6d51131c0f1d4a92e7893edcc7a28
---
v3: New, generalized from earlier x86-only version. LAST() (now
    LASTARG()) moved to macros.h.
---
TBD: What to set CODE_ALIGN to by default? Or should we requires arch-es
     to define that in all cases?

TBD: {CODE,DATA}_ALIGN are byte granular, such that a value of 0 can be
     specified (in case this has some special meaning on an arch;
     conceivably it could mean to use some kind of arch default). We may
     not strictly need that, and hence we could also make these power-of
     -2 values (using .p2align).

Note that we can't use ALIGN() (in place of SYM_ALIGN()) as long as we
still have ALIGN.

Note further that FUNC()'s etc "algn" parameter is intended to allow for
only no or a single argument. If we wanted to also make the fill value
customizable per call site, the constructs would need re-doing to some
degree.

--- /dev/null
+++ b/xen/include/xen/linkage.h
@@ -0,0 +1,56 @@
+#ifndef __LINKAGE_H__
+#define __LINKAGE_H__
+
+#ifdef __ASSEMBLY__
+
+#include <xen/macros.h>
+
+#ifndef CODE_ALIGN
+# define CODE_ALIGN ??
+#endif
+#ifndef CODE_FILL
+# define CODE_FILL ~0
+#endif
+
+#ifndef DATA_ALIGN
+# define DATA_ALIGN 0
+#endif
+#ifndef DATA_FILL
+# define DATA_FILL ~0
+#endif
+
+#define SYM_ALIGN(algn...) .balign algn
+
+#define SYM_L_GLOBAL(name) .globl name
+#define SYM_L_WEAK(name)   .weak name
+#define SYM_L_LOCAL(name)  /* nothing */
+
+#define SYM_T_FUNC         STT_FUNC
+#define SYM_T_DATA         STT_OBJECT
+#define SYM_T_NONE         STT_NOTYPE
+
+#define SYM(name, typ, linkage, algn...)          \
+        .type name, SYM_T_ ## typ;                \
+        SYM_L_ ## linkage(name);                  \
+        SYM_ALIGN(algn);                          \
+        name:
+
+#define END(name) .size name, . - name
+
+#define FUNC(name, algn...) \
+        SYM(name, FUNC, GLOBAL, LASTARG(CODE_ALIGN, ## algn), CODE_FILL)
+#define LABEL(name, algn...) \
+        SYM(name, NONE, GLOBAL, LASTARG(CODE_ALIGN, ## algn), CODE_FILL)
+#define DATA(name, algn...) \
+        SYM(name, DATA, GLOBAL, LASTARG(DATA_ALIGN, ## algn), DATA_FILL)
+
+#define FUNC_LOCAL(name, algn...) \
+        SYM(name, FUNC, LOCAL, LASTARG(CODE_ALIGN, ## algn), CODE_FILL)
+#define LABEL_LOCAL(name, algn...) \
+        SYM(name, NONE, LOCAL, LASTARG(CODE_ALIGN, ## algn), CODE_FILL)
+#define DATA_LOCAL(name, algn...) \
+        SYM(name, DATA, LOCAL, LASTARG(DATA_ALIGN, ## algn), DATA_FILL)
+
+#endif /*  __ASSEMBLY__ */
+
+#endif /* __LINKAGE_H__ */
--- a/xen/include/xen/macros.h
+++ b/xen/include/xen/macros.h
@@ -15,6 +15,15 @@
 #define count_args(args...) \
     count_args_(., ## args, 8, 7, 6, 5, 4, 3, 2, 1, 0)
 
+#define ARG1_(x, y...) (x)
+#define ARG2_(x, y...) ARG1_(y)
+#define ARG3_(x, y...) ARG2_(y)
+#define ARG4_(x, y...) ARG3_(y)
+
+#define ARG__(nr) ARG ## nr ## _
+#define ARG_(nr)  ARG__(nr)
+#define LASTARG(x, y...) ARG_(count_args(x, ## y))(x, ## y)
+
 /* Indirect macros required for expanded argument pasting. */
 #define PASTE_(a, b) a ## b
 #define PASTE(a, b) PASTE_(a, b)