在IBM J9下从Java 1.5升级到1.6时，使用JNI链接问题

Question

IBM J9 JVM 1.6中的某些更改（超过1.5）会导致我们遇到的链接错误，从而导致运行时异常。具体来说，我们使用JNI加载一个共享库，该库包含以下代码的对象文件：

extern _edata;
extern _etext;
extern _end;

这些是内存子系统中使用的地址，应该由链接器提供。然而，当我们编译共享库时，AIX链接器并没有链接它们（但是，如果您生成可执行文件，它会正确链接）。

JNI错误消息：

java.lang.UnsatisfiedLinkError: oas-jni (rtld: 0712-001 Symbol _edata was referenced
      from module /usr/IBM/blackbird/lib/liboas-jni.so(), but a runtime definition of the symbol was not found.
rtld: 0712-001 Symbol _etext was referenced from module /usr/IBM/blackbird/lib/liboas-jni.so(), but a runtime definition of the symbol was not found.
rtld: 0712-001 Symbol _end was referenced from module /usr/IBM/blackbird/lib/liboas-jni.so(), but a runtime definition of the symbol was not found.
rtld: 0712-002 fatal error: ex)
at java.lang.ClassLoader.loadLibraryWithPath(ClassLoader.java:1035)
at java.lang.ClassLoader.loadLibraryWithClassLoader(ClassLoader.java:999)
at java.lang.System.loadLibrary(System.java:507)
at com.integrasolv.owl.oas.OAS_Init.<clinit>(OAS_Init.java:16)
at java.lang.J9VMInternals.initializeImpl(Native Method)
at java.lang.J9VMInternals.initialize(J9VMInternals.java:201)
at com.integrasolv.owl.oas.OAS_Agent.<clinit>(OAS_Agent.java:87)
at java.lang.J9VMInternals.initializeImpl(Native Method)
at java.lang.J9VMInternals.initialize(J9VMInternals.java:201)
at blackbird.testclient.TestClient.initOwlProcesses(TestClient.java:120)
at blackbird.testclient.TestClient.main(TestClient.java:75)
Exception in thread "main" java.lang.UnsatisfiedLinkError: com/integrasolv/owl/oas/OAS_Agent.setEnv(Ljava/lang/String;Ljava/lang/String;)V
at blackbird.testclient.TestClient.initOwlProcesses(TestClient.java:120)
at blackbird.testclient.TestClient.main(TestClient.java:75)

裸骨测试文件：

// test.c
#include <stdio.h>
#include <stdlib.h>
extern char _etext, _edata, _end;
int runtest() {
    printf("First address past:n");
    printf("    program text (etext)      %10pn", &_etext);
    printf("    initialized data (edata)  %10pn", &_edata);
    printf("    uninitialized data (end)  %10pn", &_end);
    exit(EXIT_SUCCESS);
 }

编译对象文件而不链接

$ gcc -c test.c

从test.o创建共享库

$ gcc -shared -Wl,-G -o libtest.a test.c

请注意，-G包含链接器的-berok选项，忽略错误。否则，我们将在此处看到_etext、_edata和_end的一些未定义符号错误

从共享库转储符号表

$ dump -Tv libtest.a    

libtest.a:

                    ***Loader Section***
                    ***Loader Symbol Table Information***
[Index]      Value      Scn     IMEX Sclass   Type           IMPid Name
[0]     0x200006e4    .data              RW SECdef        [noIMid] __rtinit
[1]     0x00000000    undef      IMP     DS EXTref libgcc_s.a(shr.o) __cxa_finalize
[2]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) exit
[3]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) printf
[4]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) strtod
[5]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) __fd_select
[6]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) puts
[7]     0x00000000    undef      IMP     DS EXTref   libc.a(shr.o) __strtollmax
[8]     0x200006d0    .data      EXP     RW   Ldef        [noIMid] __dso_handle
[9]     0x20000750    .data      EXP     DS   Ldef        [noIMid] __init_aix_libgcc_cxa_atexit
[10]    0x20000780    .data      EXP     DS   Ldef        [noIMid] runtest
[11]    0x00000000    undef      IMP     PR EXTref              .. _etext
[12]    0x00000000    undef      IMP     PR EXTref              .. _edata
[13]    0x00000000    undef      IMP     PR EXTref              .. _end

nm输出：

$ nm libtest.a|grep _e
  _edata               U           -
  _edata               d   536872908           4
  _end                 U           -
  _end                 d   536872916           4
  _etext               U           -
  _etext               d   536872900           4

我不完全清楚这里发生了什么。在linux上，这很好用。在GNU/Linux 上的相同测试上输出nm命令

0000000000201040 D _edata
0000000000201048 B _end
000000000000082d T _etext

Answer 1

主程序（例如/usr/java*/jre/bin/java）应该导出这些符号（链接选项-Wl，-bE:esyms.sym

#! .
_etext
_edata
_end

您可以检查您的java是否导出这些符号：

dump -Tv -X32_64 /usr/java*/jre/bin/java | grep _etext