I'm inspecting the assembly language output of a C program I'm compiling for the ARM Android platform using GCC (the version included in the Android NDK).
I'm specifying the ARM instruction set which are 4 bytes in length rather than THUMB, but surprisingly, the emmited assembly language code is aligning functions to a 2 byte boundary!
Here is a sample of the generated code showing the wrong .align directive:
.Ltext0:
.global __aeabi_dmul
.global __aeabi_d2iz
.section .text.InitializeFIRFilter,"ax",%progbits
.align 2
.global InitializeFIRFilter
.type InitializeFIRFilter, %function
InitializeFIRFilter:
.fnstart
According to this document , the correct alignment should be 4 which makes sense.
I'm trying to force the alignment by using the -falign-functions=4 but it is being ignored.
Here are the build flags I'm specifying in the Android.mk file
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_ARM_MODE := arm
LOCAL_MODULE := nativeJadeMobile
LOCAL_SRC_FILES := nativeJadeMobile.c fftasm.s
LOCAL_LDLIBS := -llog
LOCAL_CFLAGS += -marm -ffast-math -O2 -march=armv6 -falign-functions=4 -save-temps -S
include $(BUILD_SHARED_LIBRARY)
Can anybody spot what am I doing wrong, or know how can I enforce the correct code alignment? Thank you very much in advance!
According to the assembler's documentation , the .align
pseudo op specifies a power of two for the ARM architecture. Therefore, the alignment is 2^2=4 bytes, which is correct.
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