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Android NDK隐藏jni动态库的内部符号表

2016-02-23 11:02 1066 查看

本文转自：http://blog.csdn.net/dj0379/article/details/17010981

写过win32程序的朋友对dll导出函数名都很熟悉，大家都可以通过.def文件或者__declspec(dllexport)来指定导出的函数名。在android下，可执行文件或者动态链接库用的是elf格式，和win32的pe格式有所不同。当编译动态链接库时，缺省的编译选项下默认所有的符号表都会导出。以android-ndk下的san-angeles例子为例，用ndk编译之后生成的jni动态库导出的符号表可以用下面命令看到（默认开发环境为win32
cygwin）：

showsource

$/path/to/ndk/buid/prebuilt/windows/arm-eabi-4.4.0/bin/arm-eabi-nm
libs/armeabi/libsanangeles.so

00003600TJava_com_example_SanAngeles_DemoGLSurfaceView_nativePause

00003638TJava_com_example_SanAngeles_DemoRenderer_nativeDone

0000367cTJava_com_example_SanAngeles_DemoRenderer_nativeInit

000035b4TJava_com_example_SanAngeles_DemoRenderer_nativeRender

00003644TJava_com_example_SanAngeles_DemoRenderer_nativeResize

00007334a_DYNAMIC

0000740ca_GLOBAL_OFFSET_TABLE_

0000577cT_Unwind_Backtrace

00004978T_Unwind_Complete

0000497cT_Unwind_DeleteException

00005758T_Unwind_ForcedUnwind

00004970T_Unwind_GetCFA

00005800T_Unwind_GetDataRelBase

00005808t_Unwind_GetGR

0000482ct_Unwind_GetGR

00005838T_Unwind_GetLanguageSpecificData

00005854T_Unwind_GetRegionStart

000057f8T_Unwind_GetTextRelBase

000056ecT_Unwind_RaiseException

00005710T_Unwind_Resume

00005734T_Unwind_Resume_or_Rethrow

000048a0t_Unwind_SetGR

000047e0T_Unwind_VRS_Get

0000528cT_Unwind_VRS_Pop

00004854T_Unwind_VRS_Set

000047cct_Unwind_decode_target2

0000577cT___Unwind_Backtrace

00005758T___Unwind_ForcedUnwind

000056ecT___Unwind_RaiseException

00005710T___Unwind_Resume

00005734T___Unwind_Resume_or_Rethrow

00003874T__adddf3

0000413cT__addsf3

000046f8T__aeabi_cfcmpeq

000046f8T__aeabi_cfcmple

000046e8T__aeabi_cfrcmple

00004090T__aeabi_d2f

00003874T__aeabi_dadd

00003e8cT__aeabi_ddiv

00003c20T__aeabi_dmul

00003868T__aeabi_drsub

00003870T__aeabi_dsub

00003b6cT__aeabi_f2d

00004770T__aeabi_f2iz

0000413cT__aeabi_fadd

0000470cT__aeabi_fcmpeq

00004748T__aeabi_fcmpge

0000475cT__aeabi_fcmpgt

00004734T__aeabi_fcmple

00004720T__aeabi_fcmplt

00004518T__aeabi_fdiv

00004380T__aeabi_fmul

00004130T__aeabi_frsub

00004138T__aeabi_fsub

00003b44T__aeabi_i2d

000042d4T__aeabi_i2f

00003770T__aeabi_idiv

00003864T__aeabi_idiv0

0000384cT__aeabi_idivmod

00003bc0T__aeabi_l2d

00004304T__aeabi_l2f

00003864T__aeabi_ldiv0

00003b20T__aeabi_ui2d

000042ccT__aeabi_ui2f

000036acT__aeabi_uidiv

00003758T__aeabi_uidivmod

00003bacT__aeabi_ul2d

000042f4T__aeabi_ul2f

00004d5cT__aeabi_unwind_cpp_pr0

00004d54W__aeabi_unwind_cpp_pr1

00004d4cW__aeabi_unwind_cpp_pr2

U__android_log_print

000076d4A__bss_end__

00007658A__bss_start

00007658A__bss_start__

00004688T__cmpsf2

w__cxa_begin_cleanup

w__cxa_call_unexpected

w__cxa_type_match

000074b8D__data_start

00003864T__div0

00003e8cT__divdf3

00004518T__divsf3

00003770T__divsi3

000076d4A__end__

00004688T__eqsf2

00006334A__exidx_end

000061a4A__exidx_start

00003b6cT__extendsfdf2

00004770T__fixsfsi

00003bc0T__floatdidf

00004304T__floatdisf

00003b44T__floatsidf

000042d4T__floatsisf

00003bacT__floatundidf

000042f4T__floatundisf

00003b20T__floatunsidf

000042ccT__floatunsisf

00004678T__gesf2

00004f04T__gnu_Unwind_Backtrace

w__gnu_Unwind_Find_exidx

000050e8T__gnu_Unwind_ForcedUnwind

0000515cT__gnu_Unwind_RaiseException

0000560cT__gnu_Unwind_Restore_VFP

0000561cT__gnu_Unwind_Restore_VFP_D

0000562cT__gnu_Unwind_Restore_VFP_D_16_to_31

000056c4T__gnu_Unwind_Restore_WMMXC

0000563cT__gnu_Unwind_Restore_WMMXD

00005220T__gnu_Unwind_Resume

00005200T__gnu_Unwind_Resume_or_Rethrow

00005614T__gnu_Unwind_Save_VFP

00005624T__gnu_Unwind_Save_VFP_D

00005634T__gnu_Unwind_Save_VFP_D_16_to_31

000056d8T__gnu_Unwind_Save_WMMXC

00005680T__gnu_Unwind_Save_WMMXD

00005864T__gnu_unwind_execute

00005be0T__gnu_unwind_frame

0000499ct__gnu_unwind_pr_common

00004678T__gtsf2

00004680T__lesf2

00004680T__ltsf2

00003c20T__muldf3

00004380T__mulsf3

00004688T__nesf2

000055f8T__restore_core_regs

00003870T__subdf3

00004138T__subsf3

00004090T__truncdfsf2

000036acT__udivsi3

000076d4A_bss_end__

00007658A_edata

000076d4A_end

00003590t_getTime

00080000N_stack

Uabort

000020c8TappDeinit

00002238TappInit

00002ee0TappRender

Ucos

00001ec8tdrawGLObject

00001f18tdrawModels

free

000020a8tfreeGLObject

00007654DgAppAlive

00004d64tget_eit_entry

Ugettimeofday

UglBlendFunc

UglClear

UglClearColorx

UglColor4x

UglColorPointer

UglDisable

UglDisableClientState

UglDrawArrays

UglEnable

UglEnableClientState

UglFrustumx

UglLightxv

UglLoadIdentity

UglMaterialx

UglMaterialxv

UglMatrixMode

UglMultMatrixx

UglNormalPointer

UglPopMatrix

UglPushMatrix

UglRotatex

UglScalex

UglShadeModel

UglTranslatex

UglVertexPointer

UglViewport

00001e1cTimportGLDeinit

00001e18TimportGLInit

000075ecdlight0Diffuse.3407

000075dcdlight0Position.3406

0000760cdlight1Diffuse.3409

000075fcdlight1Position.3408

0000762cdlight2Diffuse.3411

0000761cdlight2Position.3410

Umalloc

0000763cdmaterialSpecular.3412

Umemcpy

000020f4tnewGLObject

000057a0tnext_unwind_byte

Upow

0000610crquadVertices.3337

000055f8Trestore_core_regs

00004e98trestore_non_core_regs

000074bcdsCamTracks

000076bcbsCurrentCamTrack

000076c0bsCurrentCamTrackStartTick

000076c4bsDemoStopped

000076b4bsGroundPlane

000074b8dsNextCamTrackStartTick

00007658bsRandomSeed

000076b8bsStartTick

0000765cbsSuperShapeObjects

00005c20rsSuperShapeParams

000076b0bsTick

000076c8bsTimeOffset

000076d0bsTimeOffsetInit

000076ccbsTimeStopped

00007650dsWindowHeight

0000764cdsWindowWidth

000048e4tsearch_EIT_table

000048cctselfrel_offset31

Usin

Usqrt

00002164tssFunc

00001e20tsuperShapeMap

00005830tunwind_UCB_from_context

00005104tunwind_phase2

00004fcctunwind_phase2_forced

这里可以看到几乎所有的函数名全局变量名都会被导出。其中有Java_com_example_SanAngeles_为前缀的JNI接口函数，有importGLInit这些普通函数，有freeGLObject这些局部（static）函数，还有sStartTick等全局变量名。其实在这个动态发布的时候，只需要导出java_com_开头的jni函数就可以了，里面这些细节函数名完全不需要暴露出来。

如何做到这一点呢？首先，我们需要了解gcc新引进的选项-fvisibility=hidden，这个编译选项可以把所有的符号名（包括函数名和全局变量名）都强制标记成隐藏属性。我们可以在Android.mk中可以通过修改LOCAL_CFLAGS选项加入-fvisibility=hidden来做到这一点，这样编译之后的.so看到的符号表为：

showsource

000033d0tJava_com_example_SanAngeles_DemoGLSurfaceView_nativePause

00003408tJava_com_example_SanAngeles_DemoRenderer_nativeDone

0000344ctJava_com_example_SanAngeles_DemoRenderer_nativeInit

00003384tJava_com_example_SanAngeles_DemoRenderer_nativeRender

00003414tJava_com_example_SanAngeles_DemoRenderer_nativeResize

00007104a_DYNAMIC

000071dca_GLOBAL_OFFSET_TABLE_

0000554cT_Unwind_Backtrace

00004748T_Unwind_Complete

0000474cT_Unwind_DeleteException

00005528T_Unwind_ForcedUnwind

00004740T_Unwind_GetCFA

000055d0T_Unwind_GetDataRelBase

000045fct_Unwind_GetGR

000055d8t_Unwind_GetGR

00005608T_Unwind_GetLanguageSpecificData

00005624T_Unwind_GetRegionStart

000055c8T_Unwind_GetTextRelBase

000054bcT_Unwind_RaiseException

000054e0T_Unwind_Resume

00005504T_Unwind_Resume_or_Rethrow

00004670t_Unwind_SetGR

000045b0T_Unwind_VRS_Get

0000505cT_Unwind_VRS_Pop

00004624T_Unwind_VRS_Set

0000459ct_Unwind_decode_target2

0000554cT___Unwind_Backtrace

00005528T___Unwind_ForcedUnwind

000054bcT___Unwind_RaiseException

000054e0T___Unwind_Resume

00005504T___Unwind_Resume_or_Rethrow

00003644T__adddf3

00003f0cT__addsf3

000044c8T__aeabi_cfcmpeq

000044c8T__aeabi_cfcmple

000044b8T__aeabi_cfrcmple

00003e60T__aeabi_d2f

00003644T__aeabi_dadd

00003c5cT__aeabi_ddiv

000039f0T__aeabi_dmul

00003638T__aeabi_drsub

00003640T__aeabi_dsub

0000393cT__aeabi_f2d

00004540T__aeabi_f2iz

00003f0cT__aeabi_fadd

000044dcT__aeabi_fcmpeq

00004518T__aeabi_fcmpge

0000452cT__aeabi_fcmpgt

00004504T__aeabi_fcmple

000044f0T__aeabi_fcmplt

000042e8T__aeabi_fdiv

00004150T__aeabi_fmul

00003f00T__aeabi_frsub

00003f08T__aeabi_fsub

00003914T__aeabi_i2d

000040a4T__aeabi_i2f

00003540T__aeabi_idiv

00003634T__aeabi_idiv0

0000361cT__aeabi_idivmod

00003990T__aeabi_l2d

000040d4T__aeabi_l2f

00003634T__aeabi_ldiv0

000038f0T__aeabi_ui2d

0000409cT__aeabi_ui2f

0000347cT__aeabi_uidiv

00003528T__aeabi_uidivmod

0000397cT__aeabi_ul2d

000040c4T__aeabi_ul2f

00004b2cT__aeabi_unwind_cpp_pr0

00004b24W__aeabi_unwind_cpp_pr1

00004b1cW__aeabi_unwind_cpp_pr2

U__android_log_print

000074a4A__bss_end__

00007428A__bss_start

00007428A__bss_start__

00004458T__cmpsf2

w__cxa_begin_cleanup

w__cxa_call_unexpected

w__cxa_type_match

00007288D__data_start

00003634T__div0

00003c5cT__divdf3

000042e8T__divsf3

00003540T__divsi3

000074a4A__end__

00004458T__eqsf2

00006104A__exidx_end

00005f74A__exidx_start

0000393cT__extendsfdf2

00004540T__fixsfsi

00003990T__floatdidf

000040d4T__floatdisf

00003914T__floatsidf

000040a4T__floatsisf

0000397cT__floatundidf

000040c4T__floatundisf

000038f0T__floatunsidf

0000409cT__floatunsisf

00004448T__gesf2

00004cd4T__gnu_Unwind_Backtrace

w__gnu_Unwind_Find_exidx

00004eb8T__gnu_Unwind_ForcedUnwind

00004f2cT__gnu_Unwind_RaiseException

000053dcT__gnu_Unwind_Restore_VFP

000053ecT__gnu_Unwind_Restore_VFP_D

000053fcT__gnu_Unwind_Restore_VFP_D_16_to_31

00005494T__gnu_Unwind_Restore_WMMXC

0000540cT__gnu_Unwind_Restore_WMMXD

00004ff0T__gnu_Unwind_Resume

00004fd0T__gnu_Unwind_Resume_or_Rethrow

000053e4T__gnu_Unwind_Save_VFP

000053f4T__gnu_Unwind_Save_VFP_D

00005404T__gnu_Unwind_Save_VFP_D_16_to_31

000054a8T__gnu_Unwind_Save_WMMXC

00005450T__gnu_Unwind_Save_WMMXD

00005634T__gnu_unwind_execute

000059b0T__gnu_unwind_frame

0000476ct__gnu_unwind_pr_common

00004448T__gtsf2

00004450T__lesf2

00004450T__ltsf2

000039f0T__muldf3

00004150T__mulsf3

00004458T__nesf2

000053c8T__restore_core_regs

00003640T__subdf3

00003f08T__subsf3

00003e60T__truncdfsf2

0000347cT__udivsi3

000074a4A_bss_end__

00007428A_edata

000074a4A_end

00003360t_getTime

00080000N_stack

Uabort

00001e98tappDeinit

00002008tappInit

00002cb0tappRender

Ucos

00001c98tdrawGLObject

00001ce8tdrawModels

free

00001e78tfreeGLObject

00007424dgAppAlive

00004b34tget_eit_entry

Ugettimeofday

UglBlendFunc

UglClear

UglClearColorx

UglColor4x

UglColorPointer

UglDisable

UglDisableClientState

UglDrawArrays

UglEnable

UglEnableClientState

UglFrustumx

UglLightxv

UglLoadIdentity

UglMaterialx

UglMaterialxv

UglMatrixMode

UglMultMatrixx

UglNormalPointer

UglPopMatrix

UglPushMatrix

UglRotatex

UglScalex

UglShadeModel

UglTranslatex

UglVertexPointer

UglViewport

00001bectimportGLDeinit

00001be8timportGLInit

000073bcdlight0Diffuse.3407

000073acdlight0Position.3406

000073dcdlight1Diffuse.3409

000073ccdlight1Position.3408

000073fcdlight2Diffuse.3411

000073ecdlight2Position.3410

Umalloc

0000740cdmaterialSpecular.3412

Umemcpy

00001ec4tnewGLObject

00005570tnext_unwind_byte

Upow

00005edcrquadVertices.3337

000053c8Trestore_core_regs

00004c68trestore_non_core_regs

0000728cdsCamTracks

0000748cbsCurrentCamTrack

00007490bsCurrentCamTrackStartTick

00007494bsDemoStopped

00007484bsGroundPlane

00007288dsNextCamTrackStartTick

00007428bsRandomSeed

00007488bsStartTick

0000742cbsSuperShapeObjects

000059f0rsSuperShapeParams

00007480bsTick

00007498bsTimeOffset

000074a0bsTimeOffsetInit

0000749cbsTimeStopped

00007420dsWindowHeight

0000741cdsWindowWidth

000046b4tsearch_EIT_table

0000469ctselfrel_offset31

Usin

Usqrt

00001f34tssFunc

00001bf0tsuperShapeMap

00005600tunwind_UCB_from_context

00004ed4tunwind_phase2

00004d9ctunwind_phase2_forced

这里可以看到所有源代码里出现的函数名和全局变量名（符号名）都变成了't'，也就是说都是局部符号（类似于static），这样这些函数名主程序是看不到的。我们还需要把jni的入口函数变成'T'类型才行，我们可以修改jni入口函数的属性来导出这些入口函数，比如app-android.c中的Java_com_example_SanAngeles_DemoRenderer_nativeInit函数，可以改为：

showsource

void

__attribute__
((visibility(

"default"

)))

Java_com_example_SanAngeles_DemoRenderer_nativeInit(JNIEnv*env)

importGLInit();

appInit();

gAppAlive=1;

sDemoStopped=0;

sTimeOffsetInit=0;

其他几个Java_com_example_SanAngeles_开头的函数也这样修改一下即可。这样编译之后我们看到的符号表里所有Java_com_example_SanAngeles_开头的函数又变成'T'类型了。

最后我们还有一个问题就是如何隐藏那些局部符号名呢（t类型的符号）？我们可以调用strip-x来去掉这些局部的符号名。我们可以通过修改Android.mk重定义cmd-strip这个命令来实现，修改后的Android.mk如下：

showsource

LOCAL_PATH:=$(callmy-

dir

cmd-strip=$(TOOLCHAIN_PREFIX)strip--strip-debug-x$1

include$(CLEAR_VARS)

LOCAL_MODULE:=sanangeles

LOCAL_CFLAGS:=-DANDROID_NDK\

-DDISABLE_IMPORTGL\

-fvisibility=hidden

LOCAL_SRC_FILES:=\

importgl.c\

demo.c\

app-android.c\

LOCAL_LDLIBS:=-lGLESv1_CM-ldl-llog

include$(BUILD_SHARED_LIBRARY)

这样每次编译之后会自动strip掉这些局部的符号名，如下：

showsource

00003540TJava_com_example_SanAngeles_DemoGLSurfaceView_nativePause

00003578TJava_com_example_SanAngeles_DemoRenderer_nativeDone

000035bcTJava_com_example_SanAngeles_DemoRenderer_nativeInit

000034f4TJava_com_example_SanAngeles_DemoRenderer_nativeRender

00003584TJava_com_example_SanAngeles_DemoRenderer_nativeResize

000056bcT_Unwind_Backtrace

000048b8T_Unwind_Complete

000048bcT_Unwind_DeleteException

00005698T_Unwind_ForcedUnwind

000048b0T_Unwind_GetCFA

00005740T_Unwind_GetDataRelBase

00005778T_Unwind_GetLanguageSpecificData

00005794T_Unwind_GetRegionStart

00005738T_Unwind_GetTextRelBase

0000562cT_Unwind_RaiseException

00005650T_Unwind_Resume

00005674T_Unwind_Resume_or_Rethrow

00004720T_Unwind_VRS_Get

000051ccT_Unwind_VRS_Pop

00004794T_Unwind_VRS_Set

000056bcT___Unwind_Backtrace

00005698T___Unwind_ForcedUnwind

0000562cT___Unwind_RaiseException

00005650T___Unwind_Resume

00005674T___Unwind_Resume_or_Rethrow

000037b4T__adddf3

0000407cT__addsf3

00004638T__aeabi_cfcmpeq

00004638T__aeabi_cfcmple

00004628T__aeabi_cfrcmple

00003fd0T__aeabi_d2f

000037b4T__aeabi_dadd

00003dccT__aeabi_ddiv

00003b60T__aeabi_dmul

000037a8T__aeabi_drsub

000037b0T__aeabi_dsub

00003aacT__aeabi_f2d

000046b0T__aeabi_f2iz

0000407cT__aeabi_fadd

0000464cT__aeabi_fcmpeq

00004688T__aeabi_fcmpge

0000469cT__aeabi_fcmpgt

00004674T__aeabi_fcmple

00004660T__aeabi_fcmplt

00004458T__aeabi_fdiv

000042c0T__aeabi_fmul

00004070T__aeabi_frsub

00004078T__aeabi_fsub

00003a84T__aeabi_i2d

00004214T__aeabi_i2f

000036b0T__aeabi_idiv

000037a4T__aeabi_idiv0

0000378cT__aeabi_idivmod

00003b00T__aeabi_l2d

00004244T__aeabi_l2f

000037a4T__aeabi_ldiv0

00003a60T__aeabi_ui2d

0000420cT__aeabi_ui2f

000035ecT__aeabi_uidiv

00003698T__aeabi_uidivmod

00003aecT__aeabi_ul2d

00004234T__aeabi_ul2f

00004c9cT__aeabi_unwind_cpp_pr0

00004c94W__aeabi_unwind_cpp_pr1

00004c8cW__aeabi_unwind_cpp_pr2

U__android_log_print

00007614A__bss_end__

00007598A__bss_start

00007598A__bss_start__

000045c8T__cmpsf2

w__cxa_begin_cleanup

w__cxa_call_unexpected

w__cxa_type_match

000073f8D__data_start

000037a4T__div0

00003dccT__divdf3

00004458T__divsf3

000036b0T__divsi3

00007614A__end__

000045c8T__eqsf2

00006274A__exidx_end

000060e4A__exidx_start

00003aacT__extendsfdf2

000046b0T__fixsfsi

00003b00T__floatdidf

00004244T__floatdisf

00003a84T__floatsidf

00004214T__floatsisf

00003aecT__floatundidf

00004234T__floatundisf

00003a60T__floatunsidf

0000420cT__floatunsisf

000045b8T__gesf2

00004e44T__gnu_Unwind_Backtrace

w__gnu_Unwind_Find_exidx

00005028T__gnu_Unwind_ForcedUnwind

0000509cT__gnu_Unwind_RaiseException

0000554cT__gnu_Unwind_Restore_VFP

0000555cT__gnu_Unwind_Restore_VFP_D

0000556cT__gnu_Unwind_Restore_VFP_D_16_to_31

00005604T__gnu_Unwind_Restore_WMMXC

0000557cT__gnu_Unwind_Restore_WMMXD

00005160T__gnu_Unwind_Resume

00005140T__gnu_Unwind_Resume_or_Rethrow

00005554T__gnu_Unwind_Save_VFP

00005564T__gnu_Unwind_Save_VFP_D

00005574T__gnu_Unwind_Save_VFP_D_16_to_31

00005618T__gnu_Unwind_Save_WMMXC

000055c0T__gnu_Unwind_Save_WMMXD

000057a4T__gnu_unwind_execute

00005b20T__gnu_unwind_frame

000045b8T__gtsf2

000045c0T__lesf2

000045c0T__ltsf2

00003b60T__muldf3

000042c0T__mulsf3

000045c8T__nesf2

00005538T__restore_core_regs

000037b0T__subdf3

00004078T__subsf3

00003fd0T__truncdfsf2

000035ecT__udivsi3

00007614A_bss_end__

00007598A_edata

00007614A_end

00080000N_stack

Uabort

Ucos

free

Ugettimeofday

UglBlendFunc

UglClear

UglClearColorx

UglColor4x

UglColorPointer

UglDisable

UglDisableClientState

UglDrawArrays

UglEnable

UglEnableClientState

UglFrustumx

UglLightxv

UglLoadIdentity

UglMaterialx

UglMaterialxv

UglMatrixMode

UglMultMatrixx

UglNormalPointer

UglPopMatrix

UglPushMatrix

UglRotatex

UglScalex

UglShadeModel

UglTranslatex

UglVertexPointer

UglViewport

Umalloc

Umemcpy

Upow

00005538Trestore_core_regs

Usin

Usqrt

这样局部符号都没有了，只有jni入口函数被导出。这样提高了jni动态库的安全性，同时.so文件的大小也小了不少。

关于elf文件的更多资料，可以参考这篇文章。

如果要了解gcc和strip更多的选项，请移步gcc和binutils的官方文档。

补充隐藏和显示方式：

#defineDLL_LOCAL__attribute__((visibility("hidden")))

#defineDLL_CLASS__attribute__((visibility("default")))

LOCAL_CFLAGS+=-fvisibility=hidden#默认隐藏符号

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