[PATCH v2] Unwind support for ARM EABI

["Timo Teräs" <timo.teras@iki.fi>]

ARM EABI does not use the .eh_frame and .eh_frame_hdr for unwinding.
Instead the ABI specifies it's own way to unwind using .ARM.exidx and
.ARM.extab.

libgcc uses __gnu_Unwind_Find_exidx (libc must implement this) when
unwinding using exidx. This function is implemented here.
---
 arch/arm/src/find_exidx.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 arch/arm/src/find_exidx.c

diff --git a/arch/arm/src/find_exidx.c b/arch/arm/src/find_exidx.c
new file mode 100644
index 0000000..8ba9f30
--- /dev/null
+++ b/arch/arm/src/find_exidx.c
@@ -0,0 +1,46 @@
+#define _GNU_SOURCE
+#include <link.h>
+#include <stdint.h>
+
+typedef uintptr_t _Unwind_Ptr;
+
+struct find_exidx_data {
+	_Unwind_Ptr 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;
+	_Unwind_Ptr 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;
+		}
+	}
+	if (match) {
+		data->exidx_start = exidx_start;
+		data->exidx_len = exidx_len;
+	}
+	return match;
+}
+
+_Unwind_Ptr __gnu_Unwind_Find_exidx(_Unwind_Ptr 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;
+}
-- 
1.8.3.2