semihosting: Support SYS_HEAPINFO when env->boot_info is not set

env->boot_info is only set in some ARM startup paths, so we cannot
rely on it to support the SYS_HEAPINFO semihosting function. When not
available, fallback to finding a RAM memory region containing the
current stack and use the base of that.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210107170717.2098982-5-keithp@keithp.com>
Message-Id: <20210108224256.2321-16-alex.bennee@linaro.org>

hw/semihosting/arm-compat-semi.c

@@ -137,6 +137,36 @@ typedef struct GuestFD {
 
 static GArray *guestfd_array;
 
+#ifndef CONFIG_USER_ONLY
+#include "exec/address-spaces.h"
+/*
+ * Find the base of a RAM region containing the specified address
+ */
+static inline hwaddr
+common_semi_find_region_base(hwaddr addr)
+{
+    MemoryRegion *subregion;
+
+    /*
+     * Find the chunk of R/W memory containing the address.  This is
+     * used for the SYS_HEAPINFO semihosting call, which should
+     * probably be using information from the loaded application.
+     */
+    QTAILQ_FOREACH(subregion, &get_system_memory()->subregions,
+                   subregions_link) {
+        if (subregion->ram && !subregion->readonly) {
+            Int128 top128 = int128_add(int128_make64(subregion->addr),
+                                       subregion->size);
+            Int128 addr128 = int128_make64(addr);
+            if (subregion->addr <= addr && int128_lt(addr128, top128)) {
+                return subregion->addr;
+            }
+        }
+    }
+    return 0;
+}
+#endif
+
 #ifdef TARGET_ARM
 static inline target_ulong
 common_semi_arg(CPUState *cs, int argno)
@@ -175,7 +205,18 @@ common_semi_rambase(CPUState *cs)
 {
     CPUArchState *env = cs->env_ptr;
     const struct arm_boot_info *info = env->boot_info;
-    return info->loader_start;
+    target_ulong sp;
+
+    if (info) {
+        return info->loader_start;
+    }
+
+    if (is_a64(env)) {
+        sp = env->xregs[31];
+    } else {
+        sp = env->regs[13];
+    }
+    return common_semi_find_region_base(sp);
 }
 #endif