Syslinux - Oct 2008 - PATCH[001/001]: mboot.c: prefer ELF header over multiboot header

From: Ralf Ertzinger <ralf at skytale.net>

If a loaded kernel is in ELF format and contains a multiboot header indicating
valid relocation information, prefer the informations from the ELF header.
This is in violation of the Multiboot spec, but it's the way GRUB does
things and Solaris kernels rely on this behaviour.

Signed-of-by: Ralf Ertzinger <ralf at skytale.net>

---
diff --git a/com32/modules/mboot.c b/com32/modules/mboot.c
index ad659d9..2af74c1 100644
--- a/com32/modules/mboot.c
+++ b/com32/modules/mboot.c
@@ -582,71 +582,11 @@ static size_t load_kernel(struct multiboot_info *mbi, char
*cmdline)
 
         /* This kernel will do: figure out where all the pieces will live */
 
-        if (mbh->flags & MULTIBOOT_AOUT_KLUDGE) {
-
-            /* Use the offsets in the multiboot header */
-#ifdef DEBUG
-            printf("Using multiboot header.\n");
-#endif
-
-            /* Where is the code in the loaded file? */
-            seg_addr = ((char *)mbh) - (mbh->header_addr -
mbh->load_addr);
-
-            /* How much code is there? */
-            run_addr = mbh->load_addr;
-            if (mbh->load_end_addr != 0)
-                seg_size = mbh->load_end_addr - mbh->load_addr;
-            else
-                seg_size = load_size - (seg_addr - load_addr);
-
-            /* How much memory will it take up? */
-            if (mbh->bss_end_addr != 0)
-                run_size = mbh->bss_end_addr - mbh->load_addr;
-            else
-                run_size = seg_size;
-
-            if (seg_size > run_size) {
-                printf("Fatal: can't put %i bytes of kernel into %i
bytes "
-                       "of memory.\n", seg_size, run_size);
-                exit(1);
-            }
-            if (seg_addr + seg_size > load_addr + load_size) {
-                printf("Fatal: multiboot load segment runs off the "
-                       "end of the file.\n");
-                exit(1);
-            }
-
-            /* Does it fit where it wants to be? */
-            place_kernel_section(run_addr, run_size);
-
-            /* Put it on the relocation list */
-            if (seg_size < run_size) {
-                /* Set up the kernel BSS too */
-                if (seg_size > 0)
-                    add_section(run_addr, seg_addr, seg_size);
-                bss_size = run_size - seg_size;
-                add_section(run_addr + seg_size, NULL, bss_size);
-            } else {
-                /* No BSS */
-                add_section(run_addr, seg_addr, run_size);
-            }
-
-            /* Done. */
-            return mbh->entry_addr;
-
-        } else {
+        /* Look for a bootable ELF32 header */
+        if ((load_size > sizeof(Elf32_Ehdr) && 
+            BOOTABLE_I386_ELF((*((Elf32_Ehdr *) load_addr))))) {
 
-            /* Now look for an ELF32 header */
             ehdr = (Elf32_Ehdr *)load_addr;
-            if (*(unsigned long *)ehdr != 0x464c457f
-                || ehdr->e_ident[EI_DATA] != ELFDATA2LSB
-                || ehdr->e_ident[EI_CLASS] != ELFCLASS32
-                || ehdr->e_machine != EM_386)
-            {
-                printf("Fatal: kernel has neither ELF32/x86 nor multiboot
load"
-                       " headers.\n");
-                exit(1);
-            }
             if (ehdr->e_phoff + ehdr->e_phnum*sizeof (*phdr) >
load_size) {
                 printf("Fatal: malformed ELF header overruns
EOF.\n");
                 exit(1);
@@ -760,6 +700,60 @@ static size_t load_kernel(struct multiboot_info *mbi, char
*cmdline)
 
             /* Done! */
             return ehdr->e_entry;
+        } else
+        
+        /* Does the MB header specify load addresses? */
+        if (mbh->flags & MULTIBOOT_AOUT_KLUDGE) {
+
+            /* Use the offsets in the multiboot header */
+#ifdef DEBUG
+            printf("Using multiboot header.\n");
+#endif
+
+            /* Where is the code in the loaded file? */
+            seg_addr = ((char *)mbh) - (mbh->header_addr -
mbh->load_addr);
+
+            /* How much code is there? */
+            run_addr = mbh->load_addr;
+            if (mbh->load_end_addr != 0)
+                seg_size = mbh->load_end_addr - mbh->load_addr;
+            else
+                seg_size = load_size - (seg_addr - load_addr);
+
+            /* How much memory will it take up? */
+            if (mbh->bss_end_addr != 0)
+                run_size = mbh->bss_end_addr - mbh->load_addr;
+            else
+                run_size = seg_size;
+
+            if (seg_size > run_size) {
+                printf("Fatal: can't put %i bytes of kernel into %i
bytes "
+                       "of memory.\n", seg_size, run_size);
+                exit(1);
+            }
+            if (seg_addr + seg_size > load_addr + load_size) {
+                printf("Fatal: multiboot load segment runs off the "
+                       "end of the file.\n");
+                exit(1);
+            }
+
+            /* Does it fit where it wants to be? */
+            place_kernel_section(run_addr, run_size);
+
+            /* Put it on the relocation list */
+            if (seg_size < run_size) {
+                /* Set up the kernel BSS too */
+                if (seg_size > 0)
+                    add_section(run_addr, seg_addr, seg_size);
+                bss_size = run_size - seg_size;
+                add_section(run_addr + seg_size, NULL, bss_size);
+            } else {
+                /* No BSS */
+                add_section(run_addr, seg_addr, run_size);
+            }
+
+            /* Done. */
+            return mbh->entry_addr;
         }
     }