base: support gzip-compressed object files

Information
Submitter:	Curtis Dunham
Repository:	gem5
Branch:	default
Bugs:
Depends On:
Reviewers
Groups:	Default
People:

Description

Automatically detect and decompress gzip'd content in the object loader.

Testing Done

Issue Summary

Description	From	Last Updated	Status
I suggest we heave this off to separate function.	Nilay Vaish	Nov. 13, 2015, 4:02 p.m.	Resolved
nullptr	Nilay Vaish	Nov. 13, 2015, 4:02 p.m.	Resolved
nullptr	Nilay Vaish	Nov. 13, 2015, 4:02 p.m.	Resolved
Make these lines common to both if and else.	Nilay Vaish	Nov. 13, 2015, 4:02 p.m.	Dropped
I still think this code should be common to both cases. Your function doGzipLoad() should return the fd to the ...	Nilay Vaish	Nov. 24, 2015, 1:50 p.m.	Resolved
Can we use libc defined macro P_tmpdir instead of the /tmp?	Nilay Vaish	Feb. 9, 2016, 12:41 p.m.	Resolved

Any feedback or objections?

src/base/loader/object_file.cc (Diff revision 1)

I suggest we heave this off to separate function.

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src/base/loader/object_file.cc (Diff revision 1)

nullptr

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src/base/loader/object_file.cc (Diff revision 1)

nullptr

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src/base/loader/object_file.cc (Diff revision 1)

Make these lines common to both if and else.

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Curtis Dunham Nov. 13, 2015, 4:02 p.m. (Nov. 13, 2015, 4:02 p.m.)

The problem is the cleanup: the gzip library uses libc's file handling so I need to fclose for the gzip'd file but regular close() for the typical case.

Diff:

Revision 2 (+61 -8)

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src/base/loader/object_file.cc

src/base/loader/object_file.cc (Diff revision 2)

Does mmap complain with nullptr?

Curtis Dunham Nov. 16, 2015, 11:21 a.m. (Nov. 16, 2015, 11:21 a.m.)
```
No, it can be nullptr.
```

src/base/loader/object_file.cc (Diff revision 2)

I still think this code should be common to both cases.  Your function doGzipLoad() should return the fd to the tmp file you create.

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Curtis Dunham Nov. 16, 2015, 11:21 a.m. (Nov. 16, 2015, 11:21 a.m.)

because it's opened with tmpfile(), which is a libc function returning FILE*, it should be closed with fclose.  We can't return the fd after fclose()'ing it because the fd will be closed.  If we return the fd without fclose()'ing it, then gem5 will breach the contract with libc and leak memory; if we return the FILE* then the code will be messier due to even more control divergence.

Nilay Vaish Nov. 17, 2015, 11:20 a.m. (Nov. 17, 2015, 11:20 a.m.)
```
Use tmpnam.
```

Curtis Dunham Nov. 17, 2015, 11:59 a.m. (Nov. 17, 2015, 11:59 a.m.)

Ah, you mean the one that says in the man page
"BUGS
       Never use this function."? :)

I'll look into using mkstemp.

src/base/loader/object_file.cc (Diff revision 2)

Does this check fail if doGzipLoad() returns nullptr?

Curtis Dunham Nov. 16, 2015, 11:21 a.m. (Nov. 16, 2015, 11:21 a.m.)

Ah, this is a good point.  The return value from doGzipLoad should be MAP_FAILED in the two places it returns nullptr.  On Linux MAP_FAILED is all ones.