PING: RFR(S): 8240360: NativeLibraryEvent has wrong library name on Linux

[Yasumasa Suenaga]

Hi Denghui,

Your change looks good.

However, we might need to update os::get_loaded_modules_info() more.
Currently, we would get multiple jdk.NativeLibrary events from 1 library as below:

```
jdk.NativeLibrary {
   startTime = 16:59:06.621
   name = "/usr/lib64/libc-2.30.so"
   baseAddress = 0x7FDB06ACC000
   topAddress = 0x7FDB06AF1000
}

jdk.NativeLibrary {
   startTime = 16:59:06.621
   name = "/usr/lib64/libc-2.30.so"
   baseAddress = 0x7FDB06AF1000
   topAddress = 0x7FDB06C40000
}

    :

```

In addition, we would get the events even if they are not shared library as below:

```
jdk.NativeLibrary {
   startTime = 16:59:06.621
   name = "/home/ysuenaga/OpenJDK/jdk/build/linux-x86_64-server-fastdebug/images/jdk/lib/server/cl
asses.jsa"
   baseAddress = 0x800000000
   topAddress = 0x800007000
}
```

os::get_loaded_modules_info() has introduced in JDK-8056242, and it says this function is for dll/so/dylibs.
In fact, os::get_loaded_modules_info() uses EnumProcessModules() in Windows.

So I think we need to check exec bit, and merge same library to one event.
But I think it is another issue, and I'm not sure my think is correct.

Thus I agree with your change now.


Thanks,

Yasumasa (ysuenaga)


On 2020/03/20 11:12, Denghui Dong wrote:
> PING: Could you review it?
> 
> Webrev: http://cr.openjdk.java.net/~ddong/8240360/webrev.01/
> JBS: https://bugs.openjdk.java.net/browse/JDK-8240360
> 
> In Linux, EventNativeLibrary has a wrong name if the target library is located in a device whose device number (major or minor) exceeds the range of two digits.
> 
> My fix is small, use "%*s" to ignore perms, offset and device.
> 
> --- old/src/hotspot/os/linux/os_linux.cpp 2020-03-10 14:35:41.224134041 +0800
> +++ new/src/hotspot/os/linux/os_linux.cpp 2020-03-10 14:35:41.090129104 +0800
> @@ -2078,20 +2078,18 @@
> 
>       // Read line by line from 'file'
>       while (fgets(line, sizeof(line), procmapsFile) != NULL) {
> -      u8 base, top, offset, inode;
> -      char permissions[5];
> -      char device[6];
> +      u8 base, top, inode;
>         char name[sizeof(line)];
> 
> -      // Parse fields from line
> -      int matches = sscanf(line, UINT64_FORMAT_X "-" UINT64_FORMAT_X " %4s " UINT64_FORMAT_X " %5s " INT64_FORMAT " %s",
> -             &base, &top, permissions, &offset, device, &inode, name);
> -      // the last entry 'name' is empty for some entries, so we might have 6 matches instead of 7 for some lines
> -      if (matches < 6) continue;
> -      if (matches == 6) name[0] = '\0';
> +      // Parse fields from line, discard perms, offset and device
> +      int matches = sscanf(line, UINT64_FORMAT_X "-" UINT64_FORMAT_X " %*s %*s %*s " INT64_FORMAT " %s",
> +             &base, &top, &inode, name);
> +      // the last entry 'name' is empty for some entries, so we might have 3 matches instead of 4 for some lines
> +      if (matches < 3) continue;
> +      if (matches == 3) name[0] = '\0';
> 
> -      // Filter by device id '00:00' so that we only get file system mapped files.
> -      if (strcmp(device, "00:00") != 0) {
> +      // Filter by inode 0 so that we only get file system mapped files.
> +      if (inode != 0) {
> 
>           // Call callback with the fields of interest
>           if(callback(name, (address)base, (address)top, param)) {
> 
> 
> Thanks,
> Denghui Dong
> 
> 
> 
> ------------------------------------------------------------------
> From:董登辉(卓昂) <denghui.ddh at alibaba-inc.com>
> Send Time:2020年3月10日(星期二) 14:16
> To:hotspot-jfr-dev <hotspot-jfr-dev at openjdk.java.net>
> Subject:Re: RFR(S): 8240360: NativeLibraryEvent has wrong library name on Linux
> 
> Hi,
> I used a new way to fix this problem.
> Ignore "perms", "offset" and "device" fields by "%*s" so that we don't need to be concerned about the length of the device,
> and use "inode" instead of "device" for filtering.
> 
> Webrev: http://cr.openjdk.java.net/~ddong/8240360/webrev.01/
> 
> Could you review it?
> 
> Thanks,
> Denghui Dong
> ------------------------------------------------------------------
> From:董登辉(卓昂) <denghui.ddh at alibaba-inc.com>
> Send Time:2020年3月4日(星期三) 12:05
> To:hotspot-jfr-dev <hotspot-jfr-dev at openjdk.java.net>
> Subject:Re: RFR(S): 8240360: NativeLibraryEvent has wrong library name on Linux
> 
> Testing: jdk/jfr all passed.
> ------------------------------------------------------------------
> From:董登辉(卓昂) <denghui.ddh at alibaba-inc.com>
> Send Time:2020年3月3日(星期二) 22:25
> To:hotspot-jfr-dev <hotspot-jfr-dev at openjdk.java.net>
> Subject:RFR(S): 8240360: NativeLibraryEvent has wrong library name on Linux
> 
> Hi team,
> 
> I found TestNativeLibrariesEvent is always failed in my Linux environment.
> 
> The root cause is that os::get_loaded_modules_info in os_linux.cpp can not read library name correctly,
> because the device number in my Linux environment is 103:01, the format passed to sscanf can't identify
> it.
> 
> I found the limit of major and minor device number in Linux from
> https://github.com/torvalds/linux/blob/master/include/linux/kdev_t.h, and made this patch.
> 
> Please review this small change that fixes this problem.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8240360
> Webrev: http://cr.openjdk.java.net/~ddong/8240360/webrev.00/
> 
> 
> Thanks
> Denghui Dong
>