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[ELF][PPC64] Don't perform toc-indirect to toc-relative relaxation for R_PPC64_TOC16_HA not followed by R_PPC64_TOC16_LO_DS 

The current implementation assumes that R_PPC64_TOC16_HA is always followed
by R_PPC64_TOC16_LO_DS. This can break with:

// Load the address of the TOC entry, instead of the value stored at that address
  addis 3, 2, .LC0@tloc@ha  # R_PPC64_TOC16_HA
  addi  3, 3, .LC0@tloc@l   # R_PPC64_TOC16_LO
  blr

which is used by boringssl's util/fipstools/delocate/delocate.go
https://github.com/google/boringssl/blob/master/crypto/fipsmodule/FIPS.md has some documentation.
In short, this tool converts an assembly file to avoid any potential relocations.
The distance to an input .toc is not a constant after linking, so the assembly cannot use an `addis;ld` pair.
Instead, delocate changes the code to jump to a stub (`addis;addi`) which loads the TOC entry address.

Reviewed By: sfertile

Differential Revision: https://reviews.llvm.org/D78431
This commit is contained in:
Fangrui Song 2020-04-17 23:08:11 -07:00
parent 2a3cf5e583
commit 03ffe58605
2 changed files with 44 additions and 3 deletions
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13
lld/ELF/InputSection.cpp
View File

@ -949,7 +949,8 @@ void InputSectionBase::relocateAlloc(uint8_t *buf, uint8_t *bufEnd) {
assert(flags & SHF_ALLOC);
const unsigned bits = config->wordsize * 8;
for (const Relocation &rel : relocations) {
for (size_t i = 0, e = relocations.size(); i != e; ++i) {
const Relocation &rel = relocations[i];
if (rel.expr == R_NONE)
continue;
uint64_t offset = rel.offset;
@ -969,10 +970,16 @@ void InputSectionBase::relocateAlloc(uint8_t *buf, uint8_t *bufEnd) {
case R_RELAX_GOT_PC_NOPIC:
target->relaxGot(bufLoc, rel, targetVA);
break;
case R_PPC64_RELAX_TOC:
if (!tryRelaxPPC64TocIndirection(rel, bufLoc))
case R_PPC64_RELAX_TOC: {
// For R_PPC64_TOC16_HA, if it is not paired with an R_PPC64_TOC16_LO_DS,
// don't relax.
bool relax =
rel.type == R_PPC64_TOC16_LO_DS ||
(i + 1 != e && relocations[i + 1].type == R_PPC64_TOC16_LO_DS);
if (!relax || !tryRelaxPPC64TocIndirection(rel, bufLoc))
target->relocate(bufLoc, rel, targetVA);
break;
}
case R_RELAX_TLS_IE_TO_LE:
target->relaxTlsIeToLe(bufLoc, rel, targetVA);
break;

34
lld/test/ELF/ppc64-toc-relax2.s Normal file
View File

@ -0,0 +1,34 @@
# REQUIRES: ppc
# RUN: llvm-mc -filetype=obj -triple=powerpc64le %s -o %t.o
# RUN: ld.lld %t.o -o %t
# RUN: llvm-objdump -d %t | FileCheck %s
# CHECK-LABEL: <_start>:
.globl _start
_start:
## Perform toc-indirect to toc-relative relaxation even if there are unrelated instructions in between.
# CHECK-NEXT: addis 3, 2, -1
# CHECK-NEXT: li 9, 0
# CHECK-NEXT: addi 3, 3, -32768
# CHECK-NEXT: lwa 3, 0(3)
# CHECK-NEXT: li 9, 0
addis 3, 2, .LC0@toc@ha # R_PPC64_TOC16_HA
li 9, 0
ld 3, .LC0@toc@l(3) # R_PPC64_TOC16_LO_DS
lwa 3, 0(3)
li 9, 0
## The R_PPC64_TOC16_HA is not followed by an R_PPC64_TOC16_LO_DS.
## Don't perform toc-indirect to toc-relative relaxation.
# CHECK-NEXT: nop
# CHECK-NEXT: addi 3, 2, -32768
# CHECK-NEXT: blr
addis 3, 2, .LC0@toc@ha # R_PPC64_TOC16_HA
addi 3, 3, .LC0@toc@l # R_PPC64_TOC16_LO
blr
AES_encrypt:
.section .toc,"aw",@progbits
.LC0:
.tc AES_encrypt[TC], AES_encrypt