[lld][ELF] Don't apply --fix-cortex-a53-843419 to relocatable links.

[efriedma]

Summary

The code doesn't apply the fix correctly to relocatable links. I could try to fix the code that applies the fix, but it's pointless: we don't actually know what the offset will be in the final executable. So just ignore the flag for relocatable links.

Issue discovered building Android.

[MaskRay]

Can you check with GNU ld, if --fix-cortex-a53-843419 is ignored when -r is specified?

[peter.smith]

Reading the BFD source it looks like stubs (which is what errata patches like this are generated) are not added for relocatable links, I couldn't find any ld tests for them and an empirical test with:

        .section .text, "ax", %progbits
        .balign 4096
        .globl t3_ff8_ldr
        .type t3_ff8_ldr, %function
        .space 4096 - 8
t3_ff8_ldr:
        adrp x0, dat1
        ldr x1, [x1, #0]
        ldr x0, [x0, :lo12:dat1]
        ret

        .data
dat1:   .quad 1

ld.bfd will patch with a normal link and -fix-cortex-a53-843419 but will not when I add the -r.

It would be possible to make a pessimistic fix that would work during ld -r, essentially assume the worst for anything you didn't know and overalign the section to ensure the resulting alignment. However I don't think it would be practically useful due to the amount of disruption.

This same argument applies to the fix-cortex-a8 option, but that can be done in a separate patch; my fault so I'll hopefully get the time to do this tomorrow and if not, then this week.

lld/ELF/Driver.cpp

config->enableNewDtags =
       args.hasFlag(OPT_enable_new_dtags, OPT_disable_new_dtags, true);
   config->entry = args.getLastArgValue(OPT_entry);
   config->executeOnly =
       args.hasFlag(OPT_execute_only, OPT_no_execute_only, false);
   config->exportDynamic =
       args.hasFlag(OPT_export_dynamic, OPT_no_export_dynamic, false);
   config->filterList = args::getStrings(args, OPT_filter);
   config->fini = args.getLastArgValue(OPT_fini, "_fini");
-  config->fixCortexA53Errata843419 = args.hasArg(OPT_fix_cortex_a53_843419);
+  config->fixCortexA53Errata843419 = args.hasArg(OPT_fix_cortex_a53_843419) &&
+                                     !args.hasArg(OPT_relocatable);
   config->fixCortexA8 = args.hasArg(OPT_fix_cortex_a8);
   config->forceBTI = hasZOption(args, "force-bti");
   config->gcSections = args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, false);
   config->gnuUnique = args.hasFlag(OPT_gnu_unique, OPT_no_gnu_unique, true);
   config->gdbIndex = args.hasFlag(OPT_gdb_index, OPT_no_gdb_index, false);
   config->icf = getICF(args);
   config->ignoreDataAddressEquality =
       args.hasArg(OPT_ignore_data_address_equality);

lld/test/ELF/aarch64-cortex-a53-843419-recognize.s

 // REQUIRES: aarch64
 // RUN: llvm-mc -filetype=obj -triple=aarch64-none-linux %s -o %t.o
 // RUN: ld.lld -fix-cortex-a53-843419 -z separate-code -verbose %t.o -o %t2 2>&1 | FileCheck -check-prefix CHECK-PRINT %s
 // RUN: llvm-objdump -triple=aarch64-linux-gnu -d %t2 | FileCheck %s -check-prefixes=CHECK,CHECK-FIX
 // RUN: ld.lld %t.o -z separate-code -o %t3
 // RUN: llvm-objdump -triple=aarch64-linux-gnu -d %t3 | FileCheck %s -check-prefixes=CHECK,CHECK-NOFIX
+// RUN: ld.lld -fix-cortex-a53-843419 -r -z separate-code %t.o -o %t4
+// RUN: llvm-objdump -triple=aarch64-linux-gnu -d %t4 | FileCheck %s -check-prefixes=CHECK-RELOCATABLE
 // Test cases for Cortex-A53 Erratum 843419
 // See ARM-EPM-048406 Cortex_A53_MPCore_Software_Developers_Errata_Notice.pdf
 // for full erratum details.
 // In Summary
 // 1.)
 // ADRP (0xff8 or 0xffc).
 // 2.)
 // - load or store single register or either integer or vector registers.

 
 // CHECK-PRINT: detected cortex-a53-843419 erratum sequence starting at 211FF8 in unpatched output.
 // CHECK: t3_ff8_ldr:
 // CHECK-NEXT:    211ff8:        60 02 00 f0     adrp    x0, #323584
 // CHECK-NEXT:    211ffc:        21 00 40 f9     ldr             x1, [x1]
 // CHECK-FIX:     212000:        03 c8 00 14     b       #204812
 // CHECK-NOFIX:   212000:        00 00 40 f9     ldr             x0, [x0]
 // CHECK-NEXT:    212004:        c0 03 5f d6     ret
+// CHECK-RELOCATABLE: t3_ff8_ldr:
+// CHECK-RELOCATABLE-NEXT:    ff8:        00 00 00 90     adrp    x0, #0
+// CHECK-RELOCATABLE-NEXT:    ffc:        21 00 40 f9     ldr             x1, [x1]
+// CHECK-RELOCATABLE-NEXT:   1000:        00 00 40 f9     ldr             x0, [x0]
+// CHECK-RELOCATABLE-NEXT:   1004:        c0 03 5f d6     ret
+
         .section .text.01, "ax", %progbits
         .balign 4096
         .globl t3_ff8_ldr
         .type t3_ff8_ldr, %function
         .space 4096 - 8
 t3_ff8_ldr:
         adrp x0, dat1
         ldr x1, [x1, #0]