Assembly Primer Part 2 — Memory Organisation — SPU

These are my notes for where I can see SPU varying from ia32, as presented in the video Part 2 — Virtual Memory Organization.

(I didn’t notice see any significant differences between the presented information for ia32 and PPC — apart from what was noted from the first presentation — so there’s no separate post for that arch).

To compile SimpleDemo.c to examine on the SPU, you’ll need to add the -mstdmain option to spu-gcc (or spu-elf-gcc) so that the program will correctly receive the command line options.

If you examine the /proc/$PID/maps file when running a standalone SPU program, you’ll see something like this:

00100000-00120000 r-xp 00000000 00:00 0       [vdso]
0fd70000-0fd90000 r-xp 00000000 fe:02 1590608 /lib/
0fd90000-0fda0000 rw-p 00010000 fe:02 1590608 /lib/
0fdb0000-0fdd0000 r-xp 00000000 fe:02 292441  /lib/
0fdd0000-0fde0000 rw-p 00010000 fe:02 292441  /lib/
0fdf0000-0fe00000 r-xp 00000000 fe:02 292418  /lib/
0fe00000-0fe10000 rw-p 00000000 fe:02 292418  /lib/
0fe20000-0ff90000 r-xp 00000000 fe:02 292437  /lib/
0ff90000-0ffa0000 rw-p 00160000 fe:02 292437  /lib/
0ffa0000-0ffb0000 rw-p 00000000 00:00 0
0ffc0000-0ffe0000 r-xp 00000000 fe:02 1590211 /usr/lib/
0ffe0000-0fff0000 rw-p 00010000 fe:02 1590211 /usr/lib/
10000000-10010000 r-xp 00000000 fe:02 1821445 /usr/bin/elfspe
10010000-10020000 rw-p 00000000 fe:02 1821445 /usr/bin/elfspe
10020000-10050000 rwxp 00000000 00:00 0       [heap]
f7f60000-f7f70000 rw-p 00000000 00:00 0
f7f70000-f7fb0000 rw-s 00000000 00:13 9086
f7fb0000-f7fc0000 rw-p 00000000 fe:02 1463963
f7fc0000-f7fe0000 r-xp 00000000 fe:02 292430  /lib/
f7fe0000-f7ff0000 rw-p 00020000 fe:02 292430  /lib/
ffea0000-ffff0000 rw-p 00000000 00:00 0       [stack]

This is the information for the elfspe loader for the SPU program.

(The SPU’s local store is mapped into elfspe’s address space at 0xf7f7000.  This is with randomize_va_space set to zero, so it should always be in that location. This is possibly useful…)

There is no equivalent of this for the SPU program itself as there is no virtual memory mapping required (or possible) within the local store.  The state of the SPU’s memory state may be examined externally through the spufs interface provided (in this case, the file /spu/spethread-2971-268566640/mem from the above listing may be used to access the current SPU LS state). Or, of course, using gdb.

Previous assembly primer notes…

Part 1 — System Organization — PPCSPU

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