AArch64: Fix assertions in processing dynamic relocations

This patch provides the following changes in fixup_gdt_reloc()
function:
- Fixes assertions in processing dynamic relocations, when
relocation entries not matching R_AARCH64_RELATIVE type are found.
Linker might generate entries of relocation type R_AARCH64_NONE
(code 0), which should be ignored to make the code boot. Similar
issue was fixed in OP-TEE (see optee_os/ldelf/ta_elf_rel.c
commit 7a4dc765c133125428136a496a7644c6fec9b3c2)
- Fixes bug when "b.ge" (signed greater than or equal) condition
codes were used instead of "b.hs" (greater than or equal) for
comparison of absolute addresses.
- Adds optimisation which skips fixing Global Object Table (GOT)
entries when offset value is 0.

Change-Id: I35e34e055b7476843903859be947b883a1feb1b5
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>

diff --git a/lib/aarch64/misc_helpers.S b/lib/aarch64/misc_helpers.S
index 052891683f756f4900b2c5087bedcf0658c18f07..b6f6c9d88191c9c4049279ff0da36d76c70550c0 100644 (file)
--- a/lib/aarch64/misc_helpers.S
+++ b/lib/aarch64/misc_helpers.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2021, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -486,15 +486,20 @@ endfunc enable_vfp
  * arguments (which is usually the limits of the relocable BL image).
  *   x0 -  the start of the fixup region
  *   x1 -  the limit of the fixup region
- * These addresses have to be page (4KB aligned).
+ * These addresses have to be 4KB page aligned.
  * ---------------------------------------------------------------------------
  */
+
+/* Relocation codes */
+#define        R_AARCH64_NONE          0
+#define        R_AARCH64_RELATIVE      1027
+
 func fixup_gdt_reloc
        mov     x6, x0
        mov     x7, x1
 
-       /* Test if the limits are 4K aligned */
 #if ENABLE_ASSERTIONS
+       /* Test if the limits are 4KB aligned */
        orr     x0, x0, x1
        tst     x0, #(PAGE_SIZE_MASK)
        ASM_ASSERT(eq)
@@ -505,7 +510,8 @@ func fixup_gdt_reloc
         * fixup region.
         */
        and     x2, x30, #~(PAGE_SIZE_MASK)
-       sub     x0, x2, x6      /* Diff(S) = Current Address - Compiled Address */
+       subs    x0, x2, x6      /* Diff(S) = Current Address - Compiled Address */
+       b.eq    3f              /* Diff(S) = 0. No relocation needed */
 
        adrp    x1, __GOT_START__
        add     x1, x1, :lo12:__GOT_START__
@@ -518,31 +524,32 @@ func fixup_gdt_reloc
         * The new_addr is the address currently the binary is executing from
         * and old_addr is the address at compile time.
         */
-1:
-       ldr     x3, [x1]
+1:     ldr     x3, [x1]
+
        /* Skip adding offset if address is < lower limit */
        cmp     x3, x6
        b.lo    2f
+
        /* Skip adding offset if address is >= upper limit */
        cmp     x3, x7
-       b.ge    2f
+       b.hs    2f
        add     x3, x3, x0
        str     x3, [x1]
-2:
-       add     x1, x1, #8
+
+2:     add     x1, x1, #8
        cmp     x1, x2
        b.lo    1b
 
        /* Starting dynamic relocations. Use adrp/adr to get RELA_START and END */
-       adrp    x1, __RELA_START__
+3:     adrp    x1, __RELA_START__
        add     x1, x1, :lo12:__RELA_START__
        adrp    x2, __RELA_END__
        add     x2, x2, :lo12:__RELA_END__
+
        /*
         * According to ELF-64 specification, the RELA data structure is as
         * follows:
-        *      typedef struct
-        *      {
+        *      typedef struct {
         *              Elf64_Addr r_offset;
         *              Elf64_Xword r_info;
         *              Elf64_Sxword r_addend;
@@ -550,16 +557,19 @@ func fixup_gdt_reloc
         *
         * r_offset is address of reference
         * r_info is symbol index and type of relocation (in this case
-        * 0x403 which corresponds to R_AARCH64_RELATIVE).
+        * code 1027 which corresponds to R_AARCH64_RELATIVE).
         * r_addend is constant part of expression.
         *
         * Size of Elf64_Rela structure is 24 bytes.
         */
-1:
-       /* Assert that the relocation type is R_AARCH64_RELATIVE */
+
+       /* Skip R_AARCH64_NONE entry with code 0 */
+1:     ldr     x3, [x1, #8]
+       cbz     x3, 2f
+
 #if ENABLE_ASSERTIONS
-       ldr     x3, [x1, #8]
-       cmp     x3, #0x403
+       /* Assert that the relocation type is R_AARCH64_RELATIVE */
+       cmp     x3, #R_AARCH64_RELATIVE
        ASM_ASSERT(eq)
 #endif
        ldr     x3, [x1]        /* r_offset */
@@ -569,9 +579,10 @@ func fixup_gdt_reloc
        /* Skip adding offset if r_addend is < lower limit */
        cmp     x4, x6
        b.lo    2f
+
        /* Skip adding offset if r_addend entry is >= upper limit */
        cmp     x4, x7
-       b.ge    2f
+       b.hs    2f
 
        add     x4, x0, x4      /* Diff(S) + r_addend */
        str     x4, [x3]
@@ -579,6 +590,5 @@ func fixup_gdt_reloc
 2:     add     x1, x1, #24
        cmp     x1, x2
        b.lo    1b
-
        ret
 endfunc fixup_gdt_reloc