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| -rw-r--r-- | src/arch/x86_64.md | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/src/arch/x86_64.md b/src/arch/x86_64.md index ee5455e..265bd8a 100644 --- a/src/arch/x86_64.md +++ b/src/arch/x86_64.md @@ -67,6 +67,16 @@ wrmsr // Write MSR register, effectively does MSR[ECX] <- EDX:EAX ``` > See [guest64-msr.S][mkvm-msr] as an example. +#### Some interesting MSRs +- `C000_0082: IA32_LSTAR` target address for [`syscall`][x86-syscall] instruction + in **IA-32e** (64 bit) mode. +- `C000_0100: IA32_FS_BASE` storage for **%fs** segment base address. +- `C000_0101: IA32_GS_BASE` storage for **%gs** segment base address. +- `C000_0102: IA32_KERNEL_GS_BASE` additional register, [`swapgs`][x86-swapgs] + swaps **GS_BASE** and **KERNEL_GS_BASE**, without altering any register state. + Can be used to swap in a pointer to a kernel data structure on syscall entry, + as for example in [`entry_SYSCALL_64`][linux-swapgs]. + ## Size directives Explicitly specify size of the operation. ```x86asm @@ -478,3 +488,6 @@ itself. [juicebox]: https://github.com/johannst/juicebox-asm [mbr]: https://en.wikipedia.org/wiki/Master_boot_record [mkvm-msr]: https://github.com/johannst/mini-kvm-rs/blob/main/guest/guest64-msr.S +[linux-swapgs]: https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/entry/entry_64.S?h=v6.13#n87 +[x86-syscall]: https://www.felixcloutier.com/x86/syscall +[x86-swapgs]: https://www.felixcloutier.com/x86/swapgs |