Add ASCII art boot logo

It's only printed when booting the Linux kernel.  Feel free to improve the
quality of the ASCII art.  It looks like this when rendered:

              vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
                  vvvvvvvvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrr       vvvvvvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrrrrr      vvvvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrrrrrrr    vvvvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrrrrrrr    vvvvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrrrrrrr    vvvvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrrrrr      vvvvvvvvvvvvvvvvvvvvvv
rrrrrrrrrrrrr       vvvvvvvvvvvvvvvvvvvvvv
rr                vvvvvvvvvvvvvvvvvvvvvv
rr            vvvvvvvvvvvvvvvvvvvvvvvv      rr
rrrr      vvvvvvvvvvvvvvvvvvvvvvvvvv      rrrr
rrrrrr      vvvvvvvvvvvvvvvvvvvvvv      rrrrrr
rrrrrrrr      vvvvvvvvvvvvvvvvvv      rrrrrrrr
rrrrrrrrrr      vvvvvvvvvvvvvv      rrrrrrrrrr
rrrrrrrrrrrr      vvvvvvvvvv      rrrrrrrrrrrr
rrrrrrrrrrrrrr      vvvvvv      rrrrrrrrrrrrrr
rrrrrrrrrrrrrrrr      vv      rrrrrrrrrrrrrrrr
rrrrrrrrrrrrrrrrrr          rrrrrrrrrrrrrrrrrr
rrrrrrrrrrrrrrrrrrrr      rrrrrrrrrrrrrrrrrrrr
rrrrrrrrrrrrrrrrrrrrrr  rrrrrrrrrrrrrrrrrrrrrr

       INSTRUCTION SETS WANT TO BE FREE

7 files changed, 78 insertions, 0 deletions

diff --git a/config.h.in b/config.h.in
index c23bf16..c15bc0a 100644
--- a/config.h.in
+++ b/config.h.in
@@ -27,6 +27,9 @@
 /* Define if floating-point emulation is enabled */
 #undef PK_ENABLE_FP_EMULATION
 
+/* Define if the RISC-V logo is to be displayed */
+#undef PK_ENABLE_LOGO
+
 /* Define if virtual memory support is enabled */
 #undef PK_ENABLE_VM
 
diff --git a/configure b/configure
index a6f4ffe..de70ae6 100755
--- a/configure
+++ b/configure
@@ -1301,6 +1301,7 @@ Optional Features:
   --enable-optional-subprojects
                           Enable all optional subprojects
   --disable-vm            Disable virtual memory
+  --disable-logo          Disable boot logo
   --disable-fp-emulation  Disable floating-point emulation
   --disable-atomics       Emulate atomic ops nonatomically
 
@@ -4047,6 +4048,19 @@ $as_echo "#define PK_ENABLE_VM /**/" >>confdefs.h
 
 fi
 
+# Check whether --enable-vm was given.
+if test "${enable_vm+set}" = set; then :
+  enableval=$enable_vm;
+fi
+
+if test "x$enable_logo" != "xno"; then :
+
+
+$as_echo "#define PK_ENABLE_LOGO /**/" >>confdefs.h
+
+
+fi
+
 # Check whether --enable-fp-emulation was given.
 if test "${enable_fp_emulation+set}" = set; then :
   enableval=$enable_fp_emulation;
diff --git a/pk/init.c b/pk/init.c
index fd9c819..a3f22d9 100644
--- a/pk/init.c
+++ b/pk/init.c
@@ -93,6 +93,9 @@ uintptr_t boot_loader(struct mainvars* args)
 
   if (current.is_supervisor) {
     supervisor_vm_init();
+#ifdef PK_ENABLE_LOGO
+    print_logo();
+#endif
     write_csr(mepc, current.entry);
     asm volatile("eret");
     __builtin_unreachable();
diff --git a/pk/logo.c b/pk/logo.c
new file mode 100644
index 0000000..8f868e8
--- /dev/null
+++ b/pk/logo.c
@@ -0,0 +1,51 @@
+#include <string.h>
+#include "file.h"
+
+#define W 46
+#define D 21
+#define T 5
+
+void print_logo()
+{
+  static const char end[] = "\n       INSTRUCTION SETS WANT TO BE FREE\n\n";
+  static const char fill[T] = {'r', ' ', 'v', ' ', 'r'};
+  static const char logo[D][T] =
+   {{0, 14, 46, 46, 46},
+    {0, 18, 46, 46, 46},
+    {13, 20, 46, 46, 46},
+    {16, 22, 46, 46, 46},
+    {18, 22, 46, 46, 46},
+    {18, 22, 46, 46, 46},
+    {18, 22, 46, 46, 46},
+    {16, 22, 44, 46, 46},
+    {13, 20, 42, 46, 46},
+    {2, 18, 40, 46, 46},
+    {2, 14, 38, 44, 46},
+    {4, 10, 36, 42, 46},
+    {6, 12, 34, 40, 46},
+    {8, 14, 32, 38, 46},
+    {10, 16, 30, 36, 46},
+    {12, 18, 28, 34, 46},
+    {14, 20, 26, 32, 46},
+    {16, 22, 24, 30, 46},
+    {18, 22, 22, 28, 46},
+    {20, 20, 20, 26, 46},
+    {22, 22, 22, 24, 46}};
+
+  char result[D*(W+1) + sizeof(end)];
+  char* pos = result;
+  for (size_t i = 0; i < D; i++) {
+    for (size_t j = 0, p = 0; j < T; j++) {
+      if (p == logo[i][j])
+        continue;
+      do {
+        *pos++ = fill[j];
+        p++;
+      } while (p < logo[i][j]);
+    }
+    *pos++ = '\n';
+  }
+  memcpy(pos, end, sizeof(end));
+
+  file_write(stderr, result, (pos - result) + sizeof(end));
+}
diff --git a/pk/pk.ac b/pk/pk.ac
index fdcaa65..03af889 100644
--- a/pk/pk.ac
+++ b/pk/pk.ac
@@ -3,6 +3,11 @@ AS_IF([test "x$enable_vm" != "xno"], [
   AC_DEFINE([PK_ENABLE_VM],,[Define if virtual memory support is enabled])
 ])
 
+AC_ARG_ENABLE([vm], AS_HELP_STRING([--disable-logo], [Disable boot logo]))
+AS_IF([test "x$enable_logo" != "xno"], [
+  AC_DEFINE([PK_ENABLE_LOGO],,[Define if the RISC-V logo is to be displayed])
+])
+
 AC_ARG_ENABLE([fp-emulation], AS_HELP_STRING([--disable-fp-emulation], [Disable floating-point emulation]))
 AS_IF([test "x$enable_fp_emulation" != "xno"], [
   AC_DEFINE([PK_ENABLE_FP_EMULATION],,[Define if floating-point emulation is enabled])
diff --git a/pk/pk.h b/pk/pk.h
index 2df80e4..5b9f3dd 100644
--- a/pk/pk.h
+++ b/pk/pk.h
@@ -52,6 +52,7 @@ int snprintf(char* out, size_t n, const char* s, ...);
 void init_tf(trapframe_t*, long pc, long sp, int user64);
 void start_user(trapframe_t* tf) __attribute__((noreturn));
 void dump_tf(trapframe_t*);
+void print_logo();
 
 void unhandled_trap(trapframe_t*);
 void handle_misaligned_load(trapframe_t*);
diff --git a/pk/pk.mk.in b/pk/pk.mk.in
index 72f4412..3c0b455 100644
--- a/pk/pk.mk.in
+++ b/pk/pk.mk.in
@@ -24,6 +24,7 @@ pk_c_srcs = \
 	console.c \
 	vm.c \
 	string.c \
+	logo.c \
 
 pk_asm_srcs = \
 	mentry.S \