semihosting/arm-compat: replace heuristic for softmmu SYS_HEAPINFO

The previous numbers were a guess at best and rather arbitrary without
taking into account anything that might be loaded. Instead of using
guesses based on the state of registers implement a new function that:

 a) scans the MemoryRegions for the largest RAM block
 b) iterates through all "ROM" blobs looking for the biggest gap

The "ROM" blobs include all code loaded via -kernel and the various
-device loader techniques.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Andrew Strauss <astrauss11@gmail.com>
Cc: Keith Packard <keithp@keithp.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220225172021.3493923-18-alex.bennee@linaro.org>

1 files changed, 86 insertions, 0 deletions

diff --git a/hw/core/loader.c b/hw/core/loader.c
index 19edb928e9..ca2f2431fb 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -1333,6 +1333,92 @@ static Rom *find_rom(hwaddr addr, size_t size)
     return NULL;
 }
 
+typedef struct RomSec {
+    hwaddr base;
+    int se; /* start/end flag */
+} RomSec;
+
+
+/*
+ * Sort into address order. We break ties between rom-startpoints
+ * and rom-endpoints in favour of the startpoint, by sorting the 0->1
+ * transition before the 1->0 transition. Either way round would
+ * work, but this way saves a little work later by avoiding
+ * dealing with "gaps" of 0 length.
+ */
+static gint sort_secs(gconstpointer a, gconstpointer b)
+{
+    RomSec *ra = (RomSec *) a;
+    RomSec *rb = (RomSec *) b;
+
+    if (ra->base == rb->base) {
+        return ra->se - rb->se;
+    }
+    return ra->base > rb->base ? 1 : -1;
+}
+
+static GList *add_romsec_to_list(GList *secs, hwaddr base, int se)
+{
+   RomSec *cand = g_new(RomSec, 1);
+   cand->base = base;
+   cand->se = se;
+   return g_list_prepend(secs, cand);
+}
+
+RomGap rom_find_largest_gap_between(hwaddr base, size_t size)
+{
+    Rom *rom;
+    RomSec *cand;
+    RomGap res = {0, 0};
+    hwaddr gapstart = base;
+    GList *it, *secs = NULL;
+    int count = 0;
+
+    QTAILQ_FOREACH(rom, &roms, next) {
+        /* Ignore blobs being loaded to special places */
+        if (rom->mr || rom->fw_file) {
+            continue;
+        }
+        /* ignore anything finishing bellow base */
+        if (rom->addr + rom->romsize <= base) {
+            continue;
+        }
+        /* ignore anything starting above the region */
+        if (rom->addr >= base + size) {
+            continue;
+        }
+
+        /* Save the start and end of each relevant ROM */
+        secs = add_romsec_to_list(secs, rom->addr, 1);
+
+        if (rom->addr + rom->romsize < base + size) {
+            secs = add_romsec_to_list(secs, rom->addr + rom->romsize, -1);
+        }
+    }
+
+    /* sentinel */
+    secs = add_romsec_to_list(secs, base + size, 1);
+
+    secs = g_list_sort(secs, sort_secs);
+
+    for (it = g_list_first(secs); it; it = g_list_next(it)) {
+        cand = (RomSec *) it->data;
+        if (count == 0 && count + cand->se == 1) {
+            size_t gap = cand->base - gapstart;
+            if (gap > res.size) {
+                res.base = gapstart;
+                res.size = gap;
+            }
+        } else if (count == 1 && count + cand->se == 0) {
+            gapstart = cand->base;
+        }
+        count += cand->se;
+    }
+
+    g_list_free_full(secs, g_free);
+    return res;
+}
+
 /*
  * Copies memory from registered ROMs to dest. Any memory that is contained in
  * a ROM between addr and addr + size is copied. Note that this can involve