From 254e035cc27d5787348849b65619a702ae0d42e3 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Tue, 31 Dec 2019 10:42:17 +0100
Subject: handle atags in C code, print (some of) it's contents

---
 atags.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 atags.c

(limited to 'atags.c')

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
+}
-- 
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