Date: Tue, 1 Nov 2022 15:36:20 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Mark Johnston <markj@freebsd.org> Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 0e69c959150c - main - dtrace: Fix up %rip for invop probes on x86 Message-ID: <Y2Eg1FbHOlUoVuAm@kib.kiev.ua> In-Reply-To: <202210312312.29VNCH6A012822@gitrepo.freebsd.org> References: <202210312312.29VNCH6A012822@gitrepo.freebsd.org>
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On Mon, Oct 31, 2022 at 11:12:17PM +0000, Mark Johnston wrote: > The branch main has been updated by markj: > > URL: https://cgit.FreeBSD.org/src/commit/?id=0e69c959150c0ba38459e9121158016ee34b0d92 > > commit 0e69c959150c0ba38459e9121158016ee34b0d92 > Author: Mark Johnston <markj@FreeBSD.org> > AuthorDate: 2022-10-31 23:11:36 +0000 > Commit: Mark Johnston <markj@FreeBSD.org> > CommitDate: 2022-10-31 23:11:36 +0000 > > dtrace: Fix up %rip for invop probes on x86 > > When a breakpoint exception is raised, the saved value of %rip points to > the instruction following the breakpoint. However, when fetching the > value of %rip using regs[], it's more natural to provide the address of > the breakpoint itself, so modify the kinst and fbt providers accordingly. > > Reported by: khng > Reviewed by: christos, khng > MFC after: 2 months > Differential Revision: https://reviews.freebsd.org/D37218 > --- > sys/cddl/dev/fbt/x86/fbt_isa.c | 8 ++++++++ > sys/cddl/dev/kinst/amd64/kinst_isa.c | 8 +++++++- > 2 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/sys/cddl/dev/fbt/x86/fbt_isa.c b/sys/cddl/dev/fbt/x86/fbt_isa.c > index 05ec87ab437f..b05ae4cb2c44 100644 > --- a/sys/cddl/dev/fbt/x86/fbt_isa.c > +++ b/sys/cddl/dev/fbt/x86/fbt_isa.c > @@ -84,6 +84,12 @@ fbt_invop(uintptr_t addr, struct trapframe *frame, uintptr_t scratch __unused) > if ((uintptr_t)fbt->fbtp_patchpoint != addr) > continue; > fbtrval = fbt->fbtp_rval; > + > + /* > + * Report the address of the breakpoint for the benefit > + * of consumers fetching register values with regs[]. > + */ > + frame->tf_rip--; > for (; fbt != NULL; fbt = fbt->fbtp_tracenext) { > ASSERT(fbt->fbtp_rval == fbtrval); > if (fbt->fbtp_roffset == 0) { > @@ -143,6 +149,8 @@ fbt_invop(uintptr_t addr, struct trapframe *frame, uintptr_t scratch __unused) > cpu->cpu_dtrace_caller = 0; > } > } > + /* Advance to the instruction following the breakpoint. */ > + frame->tf_rip++; > return (fbtrval); > } > > diff --git a/sys/cddl/dev/kinst/amd64/kinst_isa.c b/sys/cddl/dev/kinst/amd64/kinst_isa.c > index 6d8d5d521617..e47cfbbf4d4e 100644 > --- a/sys/cddl/dev/kinst/amd64/kinst_isa.c > +++ b/sys/cddl/dev/kinst/amd64/kinst_isa.c > @@ -139,6 +139,12 @@ kinst_invop(uintptr_t addr, struct trapframe *frame, uintptr_t scratch) > if (kp == NULL) > return (0); > > + /* > + * Report the address of the breakpoint for the benefit of consumers > + * fetching register values with regs[]. > + */ > + frame->tf_rip--; > + > DTRACE_CPUFLAG_SET(CPU_DTRACE_NOFAULT); > cpu->cpu_dtrace_caller = stack[0]; > DTRACE_CPUFLAG_CLEAR(CPU_DTRACE_NOFAULT | CPU_DTRACE_BADADDR); > @@ -162,7 +168,7 @@ kinst_invop(uintptr_t addr, struct trapframe *frame, uintptr_t scratch) > > if (kpmd->reg1 == -1 && kpmd->reg2 == -1) { > /* rip-relative */ > - rval = frame->tf_rip - 1 + kpmd->instlen; > + rval = frame->tf_rip + kpmd->instlen; > } else { > /* indirect */ > rval = kinst_regval(frame, kpmd->reg1) + I am somewhat curious. Is the breakpoint used there means INT3? If yes, then %eip++ most likely points into the middle of the overwritten multibyte instruction.
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