Minor formatting updates for gvisor.dev.

* Aggregate architecture Overview in "What is gVisor?" as it makes more sense
  in one place.

* Drop "user-space kernel" and use "application kernel". The term "user-space
  kernel" is confusing when some platform implementation do not run in
  user-space (instead running in guest ring zero).

* Clear up the relationship between the Platform page in the user guide and the
  Platform page in the architecture guide, and ensure they are cross-linked.

* Restore the call-to-action quick start link in the main page, and drop the
  GitHub link (which also appears in the top-right).

* Improve image formatting by centering all doc and blog images, and move the
  image captions to the alt text.

PiperOrigin-RevId: 311845158

4 files changed, 7 insertions, 7 deletions

diff --git a/pkg/sentry/arch/syscalls_arm64.go b/pkg/sentry/arch/syscalls_arm64.go
index 92d062513..95dfd1e90 100644
--- a/pkg/sentry/arch/syscalls_arm64.go
+++ b/pkg/sentry/arch/syscalls_arm64.go
@@ -23,7 +23,7 @@ const restartSyscallNr = uintptr(128)
 //
 // In linux, at the entry of the syscall handler(el0_svc_common()), value of R0
 // is saved to the pt_regs.orig_x0 in kernel code. But currently, the orig_x0
-// was not accessible to the user space application, so we have to do the same
+// was not accessible to the userspace application, so we have to do the same
 // operation in the sentry code to save the R0 value into the App context.
 func (c *context64) SyscallSaveOrig() {
 	c.OrigR0 = c.Regs.Regs[0]
diff --git a/pkg/sentry/kernel/pipe/pipe_util.go b/pkg/sentry/kernel/pipe/pipe_util.go
index 5a1d4fd57..aacf28da2 100644
--- a/pkg/sentry/kernel/pipe/pipe_util.go
+++ b/pkg/sentry/kernel/pipe/pipe_util.go
@@ -144,7 +144,7 @@ func (p *Pipe) Ioctl(ctx context.Context, io usermem.IO, args arch.SyscallArgume
 		if v > math.MaxInt32 {
 			v = math.MaxInt32 // Silently truncate.
 		}
-		// Copy result to user-space.
+		// Copy result to userspace.
 		_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), int32(v), usermem.IOOpts{
 			AddressSpaceActive: true,
 		})
diff --git a/pkg/sentry/kernel/task_syscall.go b/pkg/sentry/kernel/task_syscall.go
index c9db78e06..a5903b0b5 100644
--- a/pkg/sentry/kernel/task_syscall.go
+++ b/pkg/sentry/kernel/task_syscall.go
@@ -199,10 +199,10 @@ func (t *Task) doSyscall() taskRunState {
 	//
 	// On x86, register rax was shared by syscall number and return
 	// value, and at the entry of the syscall handler, the rax was
-	// saved to regs.orig_rax which was exposed to user space.
+	// saved to regs.orig_rax which was exposed to userspace.
 	// But on arm64, syscall number was passed through X8, and the X0
 	// was shared by the first syscall argument and return value. The
-	// X0 was saved to regs.orig_x0 which was not exposed to user space.
+	// X0 was saved to regs.orig_x0 which was not exposed to userspace.
 	// So we have to do the same operation here to save the X0 value
 	// into the task context.
 	t.Arch().SyscallSaveOrig()
diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index 9dea2b5ff..60df51dae 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -2718,7 +2718,7 @@ func (s *socketOpsCommon) ioctl(ctx context.Context, io usermem.IO, args arch.Sy
 			v = math.MaxInt32
 		}
 
-		// Copy result to user-space.
+		// Copy result to userspace.
 		_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), int32(v), usermem.IOOpts{
 			AddressSpaceActive: true,
 		})
@@ -2787,7 +2787,7 @@ func Ioctl(ctx context.Context, ep commonEndpoint, io usermem.IO, args arch.Sysc
 		if v > math.MaxInt32 {
 			v = math.MaxInt32
 		}
-		// Copy result to user-space.
+		// Copy result to userspace.
 		_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), int32(v), usermem.IOOpts{
 			AddressSpaceActive: true,
 		})
@@ -2803,7 +2803,7 @@ func Ioctl(ctx context.Context, ep commonEndpoint, io usermem.IO, args arch.Sysc
 			v = math.MaxInt32
 		}
 
-		// Copy result to user-space.
+		// Copy result to userspace.
 		_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), int32(v), usermem.IOOpts{
 			AddressSpaceActive: true,
 		})