elfloader: port fixup_image_base to C

Porting from assembly to a higher level language makes this function more portable. Signed-off-by: Kent McLeod <[email protected]>
seL4 · Feb 1, 2022 · f3b5452 · f3b5452
1 parent 1829e9c
commit f3b5452
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Showing 2 changed files with 45 additions and 66 deletions.
diff --git a/elfloader-tool/src/arch-arm/64/crt0.S b/elfloader-tool/src/arch-arm/64/crt0.S
@@ -30,8 +30,8 @@ BEGIN_FUNC(_start)
     mov     x2, x0
     /* restore original arguments for next step */
     ldp     x0, x1, [sp, #-16]!
-    /* fixup_image_base returns 1 if no need to move */
-    cmp     x2, #1
+    /* fixup_image_base returns 0 if no need to move */
+    cmp     x2, #0
     beq     1f
     /* otherwise, jump to the start of the new elfloader */
 
@@ -41,70 +41,6 @@ BEGIN_FUNC(_start)
     b       main
 END_FUNC(_start)
 
-#ifdef CONFIG_IMAGE_BINARY
-BEGIN_FUNC(fixup_image_base)
-    stp     x29, x30, [sp, #-16]!
-    mov     x29, sp
-    ldr     x0, =IMAGE_START_ADDR
-    adr     x1, _start
-    cmp     x0, x1
-    beq     image_ok
-
-    adrp    x2, _end
-    add     x2, x2, #:lo12:_end
-    sub     x2, x2, x1
-
-    /* sanity check: don't want to overwrite ourselves! we assume
-     * everything between _start and _archive_start is important
-     * (i.e. code that might be run while relocating)
-     * but allow overlap for things after _archive_start.
-     */
-    adrp    x3, _archive_start
-    add     x3, x3, #:lo12:_archive_start
-
-    add     x4, x0, x2 /* Dest end */
-
-    /* check: if (end < archive_start && end >= _start) { abort } */
-    cmp     x4, x3
-    bge     1f
-
-    cmp     x4, x1
-    blt     1f
-
-    b       cant_reloc
-
-1:
-    /* check: if (dest < archive_start && dest >= _start) { abort } */
-    cmp     x0, x3
-    bge     2f
-
-    cmp     x0, x1
-    blt     2f
-
-cant_reloc:
-    b abort
-
-2:
-    /* x0 = desired image base */
-    /* x1 = current image space */
-    /* x2 = image size */
-    bl      memmove
-    /* x0 = dest, save it to a callee-saved register while we invalidate icache */
-    mov     x19, x0
-    bl      flush_dcache
-    bl      invalidate_icache
-    mov     x0, x19
-    b 1f
-
-image_ok:
-    /* already in the right place, just keep booting */
-    mov x0, #1
-1:
-    ldp     x29, x30, [sp], #16
-    ret
-END_FUNC(fixup_image_base)
-#endif
-
 /* Move the elf loader out of the kernel's way */
 BEGIN_FUNC(finish_relocation)
     /*

diff --git a/elfloader-tool/src/common.c b/elfloader-tool/src/common.c
@@ -29,8 +29,13 @@
 #include <platform_info.h> // this provides memory_region
 #endif
 
+#include <image_start_addr.h>
+#include <abort.h>
+
 extern char _bss[];
 extern char _bss_end[];
+extern char _start[];
+extern char _end[];
 
 /*
  * Clear the BSS segment
@@ -618,3 +623,41 @@ WEAK void platform_init(void)
 {
     /* nothing by default */
 }
+
+#ifdef CONFIG_ARCH_ARM
+extern void flush_dcache(void);
+extern void invalidate_icache(void);
+#endif
+
+/*
+ * Moves the elfloader to its expected start address in memory.
+ * This is for when the elfloader needs to be in a specific location
+ * to ensure that it doesn't occupy memory that it needs to load the
+ * kernel and user applications into.
+ */
+char * fixup_image_base(void) {
+    char *load_base = _start;
+    char *target_base = (char *) IMAGE_START_ADDR;
+    if (load_base == target_base) {
+        /* already in the right place, just keep booting */
+        return (char *)0;
+    }
+
+    /* Check that the current image location doesn't overlap with the
+     * destination location. */
+    size_t image_size = _end - _start;
+    char *target_end = target_base + image_size;
+    if ((target_base >= _start && target_base < _end) ||
+        (target_end >= _start && target_end < _end)) {
+        abort();
+    }
+
+    /* Perform the move and clean/invalidate caches if necessary */
+    char *ret = memmove(target_base, load_base, image_size);
+#ifdef CONFIG_ARCH_ARM
+    flush_dcache();
+    invalidate_icache();
+#endif
+    return ret;
+
+}