powerpc/fadump: merge adjacent memory ranges to reduce PT_LOAD segements

With dynamic memory allocation support for crash memory ranges array,
there is no hard limit on the no. of crash memory ranges kernel could
export, but program headers count could overflow in the /proc/vmcore
ELF file while exporting each memory range as PT_LOAD segment. Reduce
the likelihood of a such scenario, by folding adjacent crash memory
ranges which minimizes the total number of PT_LOAD segments.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Reviewed-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/fadump.c

@@ -908,22 +908,41 @@ static int allocate_crash_memory_ranges(void)
 static inline int fadump_add_crash_memory(unsigned long long base,
 					  unsigned long long end)
 {
+	u64  start, size;
+	bool is_adjacent = false;
+
 	if (base == end)
 		return 0;
 
-	if (crash_mem_ranges == max_crash_mem_ranges) {
-		int ret;
+	/*
+	 * Fold adjacent memory ranges to bring down the memory ranges/
+	 * PT_LOAD segments count.
+	 */
+	if (crash_mem_ranges) {
+		start = crash_memory_ranges[crash_mem_ranges - 1].base;
+		size = crash_memory_ranges[crash_mem_ranges - 1].size;
 
-		ret = allocate_crash_memory_ranges();
-		if (ret)
-			return ret;
+		if ((start + size) == base)
+			is_adjacent = true;
+	}
+	if (!is_adjacent) {
+		/* resize the array on reaching the limit */
+		if (crash_mem_ranges == max_crash_mem_ranges) {
+			int ret;
+
+			ret = allocate_crash_memory_ranges();
+			if (ret)
+				return ret;
+		}
+
+		start = base;
+		crash_memory_ranges[crash_mem_ranges].base = start;
+		crash_mem_ranges++;
 	}
 
+	crash_memory_ranges[crash_mem_ranges - 1].size = (end - start);
 	pr_debug("crash_memory_range[%d] [%#016llx-%#016llx], %#llx bytes\n",
-		crash_mem_ranges, base, end - 1, (end - base));
-	crash_memory_ranges[crash_mem_ranges].base = base;
-	crash_memory_ranges[crash_mem_ranges].size = end - base;
-	crash_mem_ranges++;
+		(crash_mem_ranges - 1), start, end - 1, (end - start));
 	return 0;
 }
 
@@ -999,6 +1018,14 @@ static int fadump_setup_crash_memory_ranges(void)
 
 	pr_debug("Setup crash memory ranges.\n");
 	crash_mem_ranges = 0;
+
+	/* allocate memory for crash memory ranges for the first time */
+	if (!max_crash_mem_ranges) {
+		ret = allocate_crash_memory_ranges();
+		if (ret)
+			return ret;
+	}
+
 	/*
 	 * add the first memory chunk (RMA_START through boot_memory_size) as
 	 * a separate memory chunk. The reason is, at the time crash firmware