hw/mips/boston: Support dumpdtb monitor commands

The boston machine doesn't set MachineState::fdt to the DTB blob that
it has loaded or created, which means that the QMP/HMP dumpdtb
monitor commands don't work.

Setting MachineState::fdt is easy in the non-FIT codepath: we can
simply do so immediately before loading the DTB into guest memory.
The FIT codepath is a bit more awkward as currently the FIT loader
throws away the memory that the FDT was in after it loads it into
guest memory.  So we add a void *pfdt argument to load_fit() for it
to store the FDT pointer into.

There is some readjustment required of the pointer handling in
loader-fit.c, so that it applies 'const' only where it should (e.g.
the data pointer we get back from fdt_getprop() is const, because
it's into the middle of the input FDT data, but the pointer that
fit_load_image_alloc() should not be const, because it's freshly
allocated memory that the caller can change if it likes).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20250206151214.2947842-5-peter.maydell@linaro.org

hw/core/loader-fit.c

@@ -32,7 +32,7 @@
 
 #define FIT_LOADER_MAX_PATH (128)
 
-static const void *fit_load_image_alloc(const void *itb, const char *name,
+static void *fit_load_image_alloc(const void *itb, const char *name,
                                   int *poff, size_t *psz, Error **errp)
 {
     const void *data;
@@ -80,11 +80,11 @@ static const void *fit_load_image_alloc(const void *itb, const char *name,
             return NULL;
         }
 
-        data = g_realloc(uncomp_data, uncomp_len);
+        uncomp_data = g_realloc(uncomp_data, uncomp_len);
         if (psz) {
             *psz = uncomp_len;
         }
-        return data;
+        return uncomp_data;
     }
 
     error_setg(errp, "unknown compression '%s'", comp);
@@ -177,13 +177,12 @@ out:
 
 static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
                         int cfg, void *opaque, const void *match_data,
-                        hwaddr kernel_end, Error **errp)
+                        hwaddr kernel_end, void **pfdt, Error **errp)
 {
     ERRP_GUARD();
     Error *err = NULL;
     const char *name;
-    const void *data;
-    const void *load_data;
+    void *data;
     hwaddr load_addr;
     int img_off;
     size_t sz;
@@ -194,7 +193,7 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
         return 0;
     }
 
-    load_data = data = fit_load_image_alloc(itb, name, &img_off, &sz, errp);
+    data = fit_load_image_alloc(itb, name, &img_off, &sz, errp);
     if (!data) {
         error_prepend(errp, "unable to load FDT image from FIT: ");
         return -EINVAL;
@@ -211,19 +210,23 @@ static int fit_load_fdt(const struct fit_loader *ldr, const void *itb,
     }
 
     if (ldr->fdt_filter) {
-        load_data = ldr->fdt_filter(opaque, data, match_data, &load_addr);
+        void *filtered_data;
+
+        filtered_data = ldr->fdt_filter(opaque, data, match_data, &load_addr);
+        if (filtered_data != data) {
+            g_free(data);
+            data = filtered_data;
+        }
     }
 
     load_addr = ldr->addr_to_phys(opaque, load_addr);
-    sz = fdt_totalsize(load_data);
-    rom_add_blob_fixed(name, load_data, sz, load_addr);
+    sz = fdt_totalsize(data);
+    rom_add_blob_fixed(name, data, sz, load_addr);
 
-    ret = 0;
+    *pfdt = data;
+    return 0;
 out:
     g_free((void *) data);
-    if (data != load_data) {
-        g_free((void *) load_data);
-    }
     return ret;
 }
 
@@ -259,7 +262,8 @@ out:
     return ret;
 }
 
-int load_fit(const struct fit_loader *ldr, const char *filename, void *opaque)
+int load_fit(const struct fit_loader *ldr, const char *filename,
+             void **pfdt, void *opaque)
 {
     Error *err = NULL;
     const struct fit_loader_match *match;
@@ -323,7 +327,7 @@ int load_fit(const struct fit_loader *ldr, const char *filename, void *opaque)
         goto out;
     }
 
-    ret = fit_load_fdt(ldr, itb, cfg_off, opaque, match_data, kernel_end,
+    ret = fit_load_fdt(ldr, itb, cfg_off, opaque, match_data, kernel_end, pfdt,
                        &err);
     if (ret) {
         error_report_err(err);

hw/mips/boston.c

@@ -358,7 +358,7 @@ static void gen_firmware(void *p, hwaddr kernel_entry, hwaddr fdt_addr)
                        kernel_entry);
 }
 
-static const void *boston_fdt_filter(void *opaque, const void *fdt_orig,
+static void *boston_fdt_filter(void *opaque, const void *fdt_orig,
                                const void *match_data, hwaddr *load_addr)
 {
     BostonState *s = BOSTON(opaque);
@@ -797,7 +797,7 @@ static void boston_mach_init(MachineState *machine)
         if (kernel_size > 0) {
             int dt_size;
             g_autofree const void *dtb_file_data = NULL;
-            g_autofree const void *dtb_load_data = NULL;
+            void *dtb_load_data = NULL;
             hwaddr dtb_paddr = QEMU_ALIGN_UP(kernel_high, 64 * KiB);
             hwaddr dtb_vaddr = cpu_mips_phys_to_kseg0(NULL, dtb_paddr);
 
@@ -815,6 +815,8 @@ static void boston_mach_init(MachineState *machine)
                 exit(1);
             }
 
+            machine->fdt = dtb_load_data;
+
             /* Calculate real fdt size after filter */
             dt_size = fdt_totalsize(dtb_load_data);
             rom_add_blob_fixed("dtb", dtb_load_data, dt_size, dtb_paddr);
@@ -822,7 +824,8 @@ static void boston_mach_init(MachineState *machine)
                                 rom_ptr(dtb_paddr, dt_size));
         } else {
             /* Try to load file as FIT */
-            fit_err = load_fit(&boston_fit_loader, machine->kernel_filename, s);
+            fit_err = load_fit(&boston_fit_loader, machine->kernel_filename,
+                               &machine->fdt, s);
             if (fit_err) {
                 error_report("unable to load kernel image");
                 exit(1);

include/hw/loader-fit.h

@@ -30,12 +30,27 @@ struct fit_loader_match {
 struct fit_loader {
     const struct fit_loader_match *matches;
     hwaddr (*addr_to_phys)(void *opaque, uint64_t addr);
-    const void *(*fdt_filter)(void *opaque, const void *fdt,
+    void *(*fdt_filter)(void *opaque, const void *fdt,
                         const void *match_data, hwaddr *load_addr);
     const void *(*kernel_filter)(void *opaque, const void *kernel,
                                  hwaddr *load_addr, hwaddr *entry_addr);
 };
 
-int load_fit(const struct fit_loader *ldr, const char *filename, void *opaque);
+/**
+ * load_fit: load a FIT format image
+ * @ldr: structure defining board specific properties and hooks
+ * @filename: image to load
+ * @pfdt: pointer to update with address of FDT blob
+ * @opaque: opaque value passed back to the hook functions in @ldr
+ * Returns: 0 on success, or a negative errno on failure
+ *
+ * @pfdt is used to tell the caller about the FDT blob. On return, it
+ * has been set to point to the FDT blob, and it is now the caller's
+ * responsibility to free that memory with g_free(). Usually the caller
+ * will want to pass in &machine->fdt here, to record the FDT blob for
+ * the dumpdtb option and QMP/HMP commands.
+ */
+int load_fit(const struct fit_loader *ldr, const char *filename, void **pfdt,
+             void *opaque);
 
 #endif /* HW_LOADER_FIT_H */