Date: Sun, 28 May 2023 14:07:46 GMT From: Dmitry Chagin <dchagin@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: a463dd810851 - main - linux(4): Add a comment explaining registers at syscall entry point on amd64 Message-ID: <202305281407.34SE7kYJ067199@gitrepo.freebsd.org>
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The branch main has been updated by dchagin: URL: https://cgit.FreeBSD.org/src/commit/?id=a463dd810851fdae5efcb8f8205d742ebf221bc8 commit a463dd810851fdae5efcb8f8205d742ebf221bc8 Author: Dmitry Chagin <dchagin@FreeBSD.org> AuthorDate: 2023-05-28 14:06:05 +0000 Commit: Dmitry Chagin <dchagin@FreeBSD.org> CommitDate: 2023-05-28 14:06:05 +0000 linux(4): Add a comment explaining registers at syscall entry point on amd64 Differential Revision: https://reviews.freebsd.org/D40153 MFC after: 1 month --- sys/amd64/linux/linux_sysvec.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/sys/amd64/linux/linux_sysvec.c b/sys/amd64/linux/linux_sysvec.c index 916ab9b687bf..89d388dc6cf8 100644 --- a/sys/amd64/linux/linux_sysvec.c +++ b/sys/amd64/linux/linux_sysvec.c @@ -124,6 +124,23 @@ LINUX_VDSO_SYM_INTPTR(kern_timekeep_base); LINUX_VDSO_SYM_INTPTR(kern_tsc_selector); LINUX_VDSO_SYM_INTPTR(kern_cpu_selector); +/* + * According to the Intel x86 ISA 64-bit syscall + * saves %rip to %rcx and rflags to %r11. Registers on syscall entry: + * %rax system call number + * %rcx return address + * %r11 saved rflags + * %rdi arg1 + * %rsi arg2 + * %rdx arg3 + * %r10 arg4 + * %r8 arg5 + * %r9 arg6 + * + * Then FreeBSD fast_syscall() move registers: + * %rcx -> trapframe.tf_rip + * %r10 -> trapframe.tf_rcx + */ static int linux_fetch_syscall_args(struct thread *td) {
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