[10] RFR(S) 8183262: noexecstack check in os::dll_load on Linux is too expensive

[Ioi Lam]

Hi Vladimir,

The changes look good. thanks for fixing this.

- Ioi


On 6/30/17 10:07 AM, Vladimir Kozlov wrote:
> webrev: http://cr.openjdk.java.net/~kvn/8183262/webrev/
> https://bugs.openjdk.java.net/browse/JDK-8183262
>
> To load AOT library we use os::dll_load() method provided on all 
> platforms.
>
> During investigation why AOT library load takes so long on Linux I 
> found that it spend most of time in ElfFile::load_tables() method 
> which looks for string tables in library. It is called from ElfFile() 
> constructor used in os::dll_load() just to check if library is built 
> with noexecstack:
>
>  if (os::uses_stack_guard_pages() && !os::Linux::_stack_is_executable) {
>    ElfFile ef(filename);
>    if (!ef.specifies_noexecstack()) {
>
> There is no need for string tables load in such case. Avoiding loads 
> helps a lot:
>
> without fix:
>
> [0.047s][info][aot,startuptime] AOT initialization, 0.0424919 secs
>
> with fix:
>
> [0.002s][info][aot,startuptime] AOT initialization, 0.0002087 secs
>
>
> Note, JDK 9 is not affected because AOT uses system dlopen() since 
> only Linux is supported.
>
> Thanks,
> Vladimir