accel/tcg: Introduce TARGET_TB_PCREL

Prepare for targets to be able to produce TBs that can
run in more than one virtual context.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/exec/cpu-defs.h

@@ -54,6 +54,9 @@
 #  error TARGET_PAGE_BITS must be defined in cpu-param.h
 # endif
 #endif
+#ifndef TARGET_TB_PCREL
+# define TARGET_TB_PCREL 0
+#endif
 
 #define TARGET_LONG_SIZE (TARGET_LONG_BITS / 8)
 

include/exec/exec-all.h

@@ -496,8 +496,32 @@ struct tb_tc {
 };
 
 struct TranslationBlock {
-    target_ulong pc;   /* simulated PC corresponding to this block (EIP + CS base) */
-    target_ulong cs_base; /* CS base for this block */
+#if !TARGET_TB_PCREL
+    /*
+     * Guest PC corresponding to this block.  This must be the true
+     * virtual address.  Therefore e.g. x86 stores EIP + CS_BASE, and
+     * targets like Arm, MIPS, HP-PA, which reuse low bits for ISA or
+     * privilege, must store those bits elsewhere.
+     *
+     * If TARGET_TB_PCREL, the opcodes for the TranslationBlock are
+     * written such that the TB is associated only with the physical
+     * page and may be run in any virtual address context.  In this case,
+     * PC must always be taken from ENV in a target-specific manner.
+     * Unwind information is taken as offsets from the page, to be
+     * deposited into the "current" PC.
+     */
+    target_ulong pc;
+#endif
+
+    /*
+     * Target-specific data associated with the TranslationBlock, e.g.:
+     * x86: the original user, the Code Segment virtual base,
+     * arm: an extension of tb->flags,
+     * s390x: instruction data for EXECUTE,
+     * sparc: the next pc of the instruction queue (for delay slots).
+     */
+    target_ulong cs_base;
+
     uint32_t flags; /* flags defining in which context the code was generated */
     uint32_t cflags;    /* compile flags */
 
@@ -573,7 +597,11 @@ struct TranslationBlock {
 /* Hide the read to avoid ifdefs for TARGET_TB_PCREL. */
 static inline target_ulong tb_pc(const TranslationBlock *tb)
 {
+#if TARGET_TB_PCREL
+    qemu_build_not_reached();
+#else
     return tb->pc;
+#endif
 }
 
 /* Hide the qatomic_read to make code a little easier on the eyes */