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[LLD] Add flag to force PLT entries to have a BTI #168365

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[LLD] Add flag to force PLT entries to have a BTI #168365

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4 changes: 2 additions & 2 deletions lld/ELF/Arch/AArch64.cpp
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Expand Up @@ -1186,8 +1186,8 @@ void AArch64BtiPac::writePlt(uint8_t *buf, const Symbol &sym,
// address may escape if referenced by a direct relocation. If relative
// vtables are used then if the vtable is in a shared object the offsets will
// be to the PLT entry. The condition is conservative.
bool hasBti = btiHeader &&
(sym.hasFlag(NEEDS_COPY) || sym.isInIplt || sym.thunkAccessed);
bool hasBti = btiHeader && (sym.hasFlag(NEEDS_COPY) || sym.isInIplt ||
sym.thunkAccessed || ctx.arg.forceBtiPlt);
if (hasBti) {
memcpy(buf, btiData, sizeof(btiData));
buf += sizeof(btiData);
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1 change: 1 addition & 0 deletions lld/ELF/Config.h
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Expand Up @@ -330,6 +330,7 @@ struct Config {
bool exportDynamic;
bool fixCortexA53Errata843419;
bool fixCortexA8;
bool forceBtiPlt = false;
bool formatBinary = false;
bool fortranCommon;
bool gcSections;
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1 change: 1 addition & 0 deletions lld/ELF/Driver.cpp
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Expand Up @@ -1486,6 +1486,7 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
ctx.arg.nmagic = args.hasFlag(OPT_nmagic, OPT_no_nmagic, false);
ctx.arg.noinhibitExec = args.hasArg(OPT_noinhibit_exec);
ctx.arg.nostdlib = args.hasArg(OPT_nostdlib);
ctx.arg.forceBtiPlt = args.hasArg(OPT_bti_plt);
ctx.arg.oFormatBinary = isOutputFormatBinary(ctx, args);
ctx.arg.omagic = args.hasFlag(OPT_omagic, OPT_no_omagic, false);
ctx.arg.optRemarksFilename = args.getLastArgValue(OPT_opt_remarks_filename);
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2 changes: 2 additions & 0 deletions lld/ELF/Options.td
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Expand Up @@ -212,6 +212,8 @@ defm eh_frame_hdr: B<"eh-frame-hdr",

def emit_relocs: F<"emit-relocs">, HelpText<"Generate relocations in output">;

def bti_plt: FF<"force-bti-plt">, HelpText<"Force all PLT entries to have BTI">;

def enable_new_dtags: F<"enable-new-dtags">,
HelpText<"Enable new dynamic tags (default)">;

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7 changes: 7 additions & 0 deletions lld/test/ELF/aarch64-feature-bti.s
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Expand Up @@ -262,6 +262,13 @@
# REPORT-ERR: error: unknown -z bti-report= value: u{{$}}
# REPORT-EMPTY:

## Force all PLT entries to start with BTI with the force-bti-plt command line option.
# RUN: ld.lld %t.o %t2.o -z force-bti --force-bti-plt %t.so -o %tforcebtiplt.exe
# RUN: llvm-objdump --no-print-imm-hex -d --mattr=+bti --no-show-raw-insn %tforcebtiplt.exe | FileCheck --check-prefix=FORCE-BTI %s

# FORCE-BTI: 00000000002103a0 <func2@plt>:
# FORCE-BTI-NEXT: 2103a0: bti c

.section ".note.gnu.property", "a"
.long 4
.long 0x10
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