handle atags in C code, print (some of) it's contents

4 files changed, 213 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index ecf2b2f..feedd79 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@ ELFFLAGS=-nostdlib -lgcc
 
 ARM_OBJECTS=kernel.o paging.o demo_functionality.o PL0_test.o uart.o loader_stage1.o loader_stage2.o
 
-KERNEL_STAGE2_OBJECTS=setup.o interrupt_vector.o interrupts.o uart.o demo_functionality.o paging.o ramfs_embeddable.o ramfs.o strings.o io.o
+KERNEL_STAGE2_OBJECTS=setup.o interrupt_vector.o interrupts.o uart.o demo_functionality.o paging.o ramfs_embeddable.o ramfs.o strings.o io.o atags.o
 
 PL_0_TEST_OBJECTS=PL0_utils.o svc.o PL0_test.o strings.o io.o
 
diff --git a/atags.c b/atags.c
new file mode 100644
index 0000000..9b88724
--- /dev/null
+++ b/atags.c
@@ -0,0 +1,99 @@
+#include "atags.h"
+#include "io.h"
+
+static inline struct atag_header *next_tag(struct atag_header *tag)
+{
+  return (struct atag_header*) (((uint32_t*) tag) + tag->size);
+}
+
+#define TAG_CONTENTS_FUN(tagname)                               \
+  static inline struct atag_##tagname *tagname##_tag_contents   \
+  (struct atag_header *tag)                                     \
+  {                                                             \
+    return (struct atag_##tagname*) (tag + 1);                  \
+  }
+
+TAG_CONTENTS_FUN(header)
+TAG_CONTENTS_FUN(core)
+TAG_CONTENTS_FUN(mem)
+TAG_CONTENTS_FUN(videotext)
+TAG_CONTENTS_FUN(ramdisk)
+TAG_CONTENTS_FUN(initrd2)
+TAG_CONTENTS_FUN(serialnr)
+TAG_CONTENTS_FUN(revision)
+TAG_CONTENTS_FUN(videolfb)
+TAG_CONTENTS_FUN(cmdline)
+
+uint32_t find_memory_size(struct atag_header *atags)
+{
+  // we silently assume there will only be one mem atag
+  while (atags->tag != ATAG_MEM && atags->tag != ATAG_NONE)
+    atags = next_tag(atags);
+
+  if (atags->tag == ATAG_NONE)
+    return 0;
+
+  struct atag_mem *mem_tag = mem_tag_contents(atags);
+
+  // our design assumes address 0x0 is available, so we reject mem
+  // atag saying otherwise
+  if (mem_tag->start != 0)
+    return 0;
+
+  return mem_tag->size;
+}
+
+void print_tag(struct atag_header *tag)
+{
+#define TAG_CASE(tagname_upcase, tagname_locase, instructions)  \
+  case ATAG_##tagname_upcase:                                   \
+    puts("ATAG_" #tagname_upcase ":");                          \
+      {                                                         \
+        struct atag_##tagname_locase *contents =                \
+          tagname_locase##_tag_contents(tag);			\
+        instructions;                                           \
+      }                                                         \
+    break
+  
+  switch (tag->tag)
+    {
+      TAG_CASE(CORE, core,
+               prints("  flags: 0x");
+               printhex(contents->flags); puts("");
+               prints("  page size: ");
+               printdec(contents->pagesize); puts("");
+               prints("  root device: ");
+               printdec(contents->rootdev); puts(""););
+      TAG_CASE(MEM, mem, 
+               prints("  memory size: 0x");
+               printhex(contents->size); puts("");
+               prints("  memory start: 0x");
+               printhex(contents->start); puts(""););
+      // the rest are unimportant for now,
+      // as they're not passed by qemu
+      TAG_CASE(VIDEOTEXT, videotext, (void) contents;);
+      TAG_CASE(RAMDISK, ramdisk, (void) contents;);
+      TAG_CASE(INITRD2, initrd2, (void) contents;);
+      TAG_CASE(SERIAL, serialnr, (void) contents;);
+      TAG_CASE(REVISION, revision, (void) contents;);
+      TAG_CASE(VIDEOLFB, videolfb, (void) contents;);
+      TAG_CASE(CMDLINE, cmdline, (void) contents;);
+
+    case ATAG_NONE:
+      puts("ATAG_NONE");
+      break;
+    default:
+      prints("!! unknown tag: 0x"); printhex(tag->tag); puts(" !!");
+    }
+}
+
+void print_atags(struct atag_header *atags)
+{
+  while (atags->tag != ATAG_NONE)
+    {
+      print_tag(atags);
+      atags = next_tag(atags);
+    }
+
+  print_tag(atags); // also print ATAG_NONE
+}
diff --git a/atags.h b/atags.h
new file mode 100644
index 0000000..4b6879f
--- /dev/null
+++ b/atags.h
@@ -0,0 +1,102 @@
+#ifndef ATAGS_H
+#define ATAGS_H
+
+#include <stdint.h>
+
+#define ATAG_NONE      0x00000000
+#define ATAG_CORE      0x54410001
+#define ATAG_MEM       0x54410002
+#define ATAG_VIDEOTEXT 0x54410003
+#define ATAG_RAMDISK   0x54410004
+#define ATAG_INITRD2   0x54420005
+#define ATAG_SERIAL    0x54410006
+#define ATAG_REVISION  0x54410007
+#define ATAG_VIDEOLFB  0x54410008
+#define ATAG_CMDLINE   0x54410009
+
+struct atag_header
+{
+  uint32_t size;
+  uint32_t tag;
+};
+
+struct atag_core
+{
+  uint32_t flags;
+  uint32_t pagesize;
+  uint32_t rootdev;
+};
+
+struct atag_mem
+{
+  uint32_t size;
+  uint32_t start;
+};
+
+struct atag_videotext
+{
+  uint8_t  x;
+  uint8_t  y;
+  uint16_t video_page;
+  uint8_t  video_mode;
+  uint8_t  video_cols;
+  uint16_t video_ega_bx;
+  uint8_t  video_lines;
+  uint8_t  video_isvga;
+  uint16_t video_points;
+};
+
+struct atag_ramdisk
+{
+  uint32_t flags;
+  uint32_t size;
+  uint32_t start;
+};
+
+struct atag_initrd2
+{
+  uint32_t start;
+  uint32_t size;
+};
+
+struct atag_serialnr
+{
+  uint32_t low;
+  uint32_t high;
+};
+
+struct atag_revision
+{
+  uint32_t rev;
+};
+
+struct atag_videolfb
+{
+  uint16_t lfb_width;
+  uint16_t lfb_height;
+  uint16_t lfb_depth;
+  uint16_t lfb_linelength;
+  uint32_t lfb_base;
+  uint32_t lfb_size;
+  uint8_t  red_size;
+  uint8_t  red_pos;
+  uint8_t  green_size;
+  uint8_t  green_pos;
+  uint8_t  blue_size;
+  uint8_t  blue_pos;
+  uint8_t  rsvd_size;
+  uint8_t  rsvd_pos;
+};
+
+struct atag_cmdline
+{
+  char cmdline[1];
+};
+
+uint32_t find_memory_size(struct atag_header *atags);
+
+void print_tag(struct atag_header *tag);
+
+void print_atags(struct atag_header *atags);
+
+#endif // ATAGS_H
diff --git a/setup.c b/setup.c
index be71547..f0a9d0a 100644
--- a/setup.c
+++ b/setup.c
@@ -2,9 +2,10 @@
 #include "io.h"
 #include "demo_functionality.h"
 #include "paging.h"
+#include "atags.h"
 
 void setup(uint32_t r0, uint32_t machine_type,
-	   uint32_t atags)
+	   struct atag_header *atags)
 {
   uart_init();
 
@@ -17,12 +18,19 @@ void setup(uint32_t r0, uint32_t machine_type,
 
   prints("ARM machine type: 0x"); printhext(machine_type); puts("");
   
-  // value 3 introduced by stage1 code, means no atags was found
+  // value 3 introduced by stage1 code means no atags was found
   if (r0 == 3)
     puts("No ATAGS was found!");
   else
     {
-      prints("ATAGS copied to 0x"); printhex(atags); puts("");
+      prints("ATAGS copied to 0x");
+      printhex((uint32_t) atags); puts("");
+
+      puts("__ ATAGS contents __");
+
+      print_atags(atags);
+
+      puts("__ end of ATAGS contents __");
     }
 
   // prints some info