Hello everyone,
I am trying to use MSR registers for experimenting on caches. I want to add
a custom MSR to the system which is simulated by Gem5 with Linux v5.4.84
kernel. I have added entries in
src/arch/x86/regs/msr.cc and src/arch/x86/regs/misc.hh on some unused
register index, say 0xc0010118.
After compiling and building gem5.opt, when I run sudo rdmsr 0xc0010118, it
says,
rdmsr: CPU 0 cannot read MSR 0xc0010118
Analysing it with strace shows that pread64 returns EIO (input/output
error).
execve("/usr/sbin/rdmsr", ["rdmsr", "0xc0010118"], 0x7fff6cbbe848 /* 12
> vars */) = 0
> brk(NULL) = 0x55774d0c6000
> arch_prctl(0x3001 /* ARCH_??? */, 0x7fff2fb9f220) = -1 EINVAL (Invalid
> argument)
> access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or
> directory)
> openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0644, st_size=25560, ...}) = 0
> mmap(NULL, 25560, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f4602db7000
> close(3) = 0
> openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
> read(3,
> "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360A\2\0\0\0\0\0"..., 832)
> = 832
> pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"...,
> 784, 64) = 784
> pread64(3,
> "\4\0\0\0\20\0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0", 32,
> 848) = 32
> pread64(3,
> "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\237\333t\347\262\27\320l\223\27*\202C\370T\177"...,
> 68, 880) = 68
> fstat(3, {st_mode=S_IFREG|0755, st_size=2029560, ...}) = 0
> mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
> 0x7f4602db5000
> pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"...,
> 784, 64) = 784
> pread64(3,
> "\4\0\0\0\20\0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0", 32,
> 848) = 32
> pread64(3,
> "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\237\333t\347\262\27\320l\223\27*\202C\370T\177"...,
> 68, 880) = 68
> mmap(NULL, 2037344, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) =
> 0x7f4602bc3000
> mmap(0x7f4602be5000, 1540096, PROT_READ|PROT_EXEC,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x22000) = 0x7f4602be5000
> mmap(0x7f4602d5d000, 319488, PROT_READ,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19a000) = 0x7f4602d5d000
> mmap(0x7f4602dab000, 24576, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e7000) = 0x7f4602dab000
> mmap(0x7f4602db1000, 13920, PROT_READ|PROT_WRITE,
> MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f4602db1000
> close(3) = 0
> arch_prctl(ARCH_SET_FS, 0x7f4602db6580) = 0
> mprotect(0x7f4602dab000, 16384, PROT_READ) = 0
> mprotect(0x55774d0c4000, 4096, PROT_READ) = 0
> mprotect(0x7f4602deb000, 4096, PROT_READ) = 0
> munmap(0x7f4602db7000, 25560) = 0
> openat(AT_FDCWD, "/dev/cpu/0/msr", O_RDONLY) = 3
> pread64(3, 0x7fff2fb9f138, 8, 3221291288) = -1 EIO (Input/output error)
> write(2, "rdmsr: CPU 0 cannot read MSR 0xc"..., 40rdmsr: CPU 0 cannot read
> MSR 0xc0010118
> ) = 40
> exit_group(4) = ?
> +++ exited with 4 +++
>
Does anyone have any experience with this or any ideas what I may be
missing?
--
Sarthak Rout,
B.Tech(CSE) '23
IIT Kanpur
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