add some ARM EABI-specific exception handling infrastructure

patch by Timo Teräs

arch/arm/src/find_exidx.c

@@ -0,0 +1,42 @@
+#define _GNU_SOURCE
+#include <link.h>
+#include <stdint.h>
+
+struct find_exidx_data {
+	uintptr_t pc, exidx_start;
+	int exidx_len;
+};
+
+static int find_exidx(struct dl_phdr_info *info, size_t size, void *ptr)
+{
+	struct find_exidx_data *data = ptr;
+	const ElfW(Phdr) *phdr = info->dlpi_phdr;
+	uintptr_t addr, exidx_start = 0;
+	int i, match = 0, exidx_len = 0;
+
+	for (i = info->dlpi_phnum; i > 0; i--, phdr++) {
+		addr = info->dlpi_addr + phdr->p_vaddr;
+		switch (phdr->p_type) {
+		case PT_LOAD:
+			match |= data->pc >= addr && data->pc < addr + phdr->p_memsz;
+			break;
+		case PT_ARM_EXIDX:
+			exidx_start = addr;
+			exidx_len = phdr->p_memsz;
+			break;
+		}
+	}
+	data->exidx_start = exidx_start;
+	data->exidx_len = exidx_len;
+	return match;
+}
+
+uintptr_t __gnu_Unwind_Find_exidx(uintptr_t pc, int *pcount)
+{
+	struct find_exidx_data data;
+	data.pc = pc;
+	if (dl_iterate_phdr(find_exidx, &data) <= 0)
+		return 0;
+	*pcount = data.exidx_len / 8;
+	return data.exidx_start;
+}