Re: i686 quirk for AMD Geode

Lennart Sorensen
2009-11-18T20:21:05Z

On Tue, Nov 17, 2009 at 01:33:57PM -0500, Lennart Sorensen wrote:
> # strace ./rdmsr -x 0x00001810
> execve("./rdmsr", ["./rdmsr", "-x", "0x00001810"], [/* 13 vars */]) = 0
> uname({sys="Linux", node="ruggedrouter", ...}) = 0
> brk(0) = 0x8106000
> access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f23000
> access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f22000
> open("/etc/ld.so.cache", O_RDONLY) = 3
> fstat64(3, {st_mode=S_IFREG|0644, st_size=14975, ...}) = 0
> mmap2(NULL, 14975, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f1e000
> close(3) = 0
> access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
> open("/lib/tls/libc.so.6", O_RDONLY) = 3
> read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\240O\1"..., 512) = 512
> fstat64(3, {st_mode=S_IFREG|0644, st_size=1245488, ...}) = 0
> mmap2(NULL, 1251484, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7dec000
> mmap2(0xb7f14000, 28672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x128) = 0xb7f14000
> mmap2(0xb7f1b000, 10396, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7f1b000
> close(3) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7deb000
> mprotect(0xb7f14000, 20480, PROT_READ) = 0
> set_thread_area({entry_number:-1 -> 6, base_addr:0xb7deb6c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
> munmap(0xb7f1e000, 14975) = 0
> open("/dev/cpu/0/msr", O_RDONLY|O_LARGEFILE) = 3
> pread64(3, 0xbf83ac00, 8, 6160) = -1 EIO (Input/output error)
> write(2, "rdmsr: CPU 0 cannot read MSR 0x0"..., 40rdmsr: CPU 0 cannot read MSR 0x00001810
> ) = 40
> exit_group(4) = ?
> Process 15044 detached

OK, I added a bit of debuging print statements to msr.c and I find that
calling rdmsr 0x1810 returns error 0xfffffff2 (-14 that is).

It seems to end up calling:

static inline unsigned long long native_read_msr_safe(unsigned int msr,
int *err)
{
DECLARE_ARGS(val, low, high);

asm volatile("2: rdmsr ; xor %0,%0\n"
"1:\n\t"
".section .fixup,\"ax\"\n\t"
"3: mov %3,%0 ; jmp 1b\n\t"
".previous\n\t"
_ASM_EXTABLE(2b, 3b)
: "=r" (*err), EAX_EDX_RET(val, low, high)
: "c" (msr), "i" (-EFAULT));
return EAX_EDX_VAL(val, low, high);
}

That unfortunately is too low level for me to make sense of.

--
Len Sorensen