Detect the sysroot path of the ARM GNU toolchain automatically

Author: DrXiao

mk/arm.mk

@@ -12,4 +12,36 @@ ARCH_DEFS = \
     \#define PLT_ENT_SIZE 12\n$\
     \#define R_ARCH_JUMP_SLOT 0x16\n$\
     "
-RUNNER_LD_PREFIX=-L /usr/arm-linux-gnueabi/
+
+# 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-gnueabi".
+#
+# For example, if the toolchain is installed under "/opt/arm",
+# the command "arm-linux-gnueabi-gcc --print-sysroot" will
+# prints "/opt/arm/sysroot", and the build system can use this
+# as LD_LINUX_PATH directly.
+CROSS_COMPILE = arm-linux-gnueabi-
+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)