Detect the sysroot path of the ARM GNU toolchain automatically

Originally, the default path of ld-linux.so is set to a specific path
for Arm architecture. However, Considering that developers may manually
install the ARM GNU toolchain, the sysroot path may not match the
default path.

This commit improves arm.mk to use a more convenient method to
automatically detect the correct sysroot path.

Author: DrXiao

mk/arm.mk

@@ -12,4 +12,38 @@ ARCH_DEFS = \
     \#define PLT_ENT_SIZE 12\n$\
     \#define R_ARCH_JUMP_SLOT 0x16\n$\
     "
-RUNNER_LD_PREFIX=-L /usr/arm-linux-gnueabihf/
+
+# Find the sysroot of the ARM GNU toolchain.
+#
+# Since developers may install the toolchain manually instead of
+# using a package manager such as apt, we cannot assume that the
+# path of ld-linux is always "/usr/arm-linux-gnueabihf".
+#
+# For example, if the toolchain is installed under "/opt/arm",
+# the command "arm-linux-gnueabihf-gcc --print-sysroot" will
+# prints "/opt/arm/sysroot", and the build system can use this
+# as LD_LINUX_PATH directly.
+ifneq ($(HOST_ARCH),$(ARCH_NAME))
+    CROSS_COMPILE = arm-linux-gnueabihf-
+    ARM_CC = $(CROSS_COMPILE)gcc
+    ARM_CC := $(shell which $(ARM_CC))
+    LD_LINUX_PATH := $(shell cd $(shell $(ARM_CC) --print-sysroot) 2>/dev/null && pwd)
+    ifeq ("$(LD_LINUX_PATH)","/")
+        LD_LINUX_PATH := $(shell dirname "$(shell which $(ARM_CC))")/..
+        LD_LINUX_PATH := $(shell cd $(LD_LINUX_PATH) 2>/dev/null && pwd)
+        LD_LINUX_PATH := $(LD_LINUX_PATH)/$(shell echo $(CROSS_COMPILE) | sed s'/.$$//')/libc
+        LD_LINUX_PATH := $(shell cd $(LD_LINUX_PATH) 2>/dev/null && pwd)
+        ifndef LD_LINUX_PATH
+            LD_LINUX_PATH = /usr/$(shell echo $(CROSS_COMPILE) | sed s'/.$$//')
+            LD_LINUX_PATH := $(shell cd $(LD_LINUX_PATH) 2>/dev/null && pwd)
+        endif
+    endif
+
+    ifeq ($(DYNLINK),1)
+        ifndef LD_LINUX_PATH
+            $(error "Dynamic linking mode requires ld-linux.so")
+        endif
+    endif
+
+    RUNNER_LD_PREFIX = -L $(LD_LINUX_PATH)
+endif