code review 199096: 6l: move mapped symbol table lower in memory

6l: move mapped symbol table lower in memory
Allows binary to run on some Linux system.

Fix for issue 365.

[adg, 2010-02-04 01:45:56]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change.

[rsc, 2010-02-04 01:51:51]

> Description:
> A malloc at a distant location upset some linux kernels.
> Solution: make the distant location not-so-distant.
> (Fix for issue #365)

Please make the first line of the description standalone;
it appears in things like the godashboard.appspot.com page
and in short summaries of hg log.
Also the syntax of the fixes line is important because
a program generates it.  Better description:

    6l: move mapped symbol table lower in memory
    Allows binary to run on some Linux systems.

    Fixes issue 365.

(You can run "hg change 199096" to edit the description
in your editor, or you can do it via the web page.)

> @@ -98,3 +101,4 @@
>  extern char*   goroot;
>  extern char*   goarch;
>  extern char*   goos;
> +

Inserted a spurious blank line here (in ld/lib.h).
Worth deleting just to keep noise out of the diff.
(I often do this myself and find it worth running
"hg d @199096" or viewing the code review before
running hg mail, just to sanity check it.)

> Index: src/pkg/runtime/symtab.c
> +#define SYMCOUNTS ((int32*)(0x99LL<<24))       // known to 8l and 8l
>  #define SYMDATA ((byte*)(0x99LL<<24) + 8)
> -#endif
> +// (This magic number also defined in src/cmd/ld/lib.h as SYMDATVA)

The two comments say the same thing.  I suggest:

  #define SYMCOUNTS ((int32*)(0x99LL<<24))       // known to 6l, 8l;
see src/cmd/ld/lib.h

Russ

[adg, 2010-02-04 04:08:42]

Hello rsc (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2010-02-04 04:11:59]

LGTM

[adg, 2010-02-04 20:46:14]

*** Submitted as http://code.google.com/p/go/source/detail?r=0cdceeba29f2 ***

6l: move mapped symbol table lower in memory
Allows binary to run on some Linux system.

Fix for issue 365.

R=rsc
CC=golang-dev
http://codereview.appspot.com/199096