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[BOLT] Support more than two jump table parents

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Multi-way splitting can cause multiple fragments to access the same jump
table. Relax the assumption that a jump table can only have up to two
parents.

Test Plan: added bolt/test/X86/three-way-split-jt.s

Reviewers: ayermolo, dcci, rafaelauler, maksfb

Reviewed By: rafaelauler, dcci

Pull Request: https://github.com/llvm/llvm-project/pull/99988
This commit is contained in:
Amir Ayupov 2024-07-24 07:16:39 -07:00 committed by GitHub
parent 83ea7ce3a1
commit 9d2dd009b6
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GPG Key ID: B5690EEEBB952194
2 changed files with 102 additions and 5 deletions
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12
bolt/lib/Core/BinaryContext.cpp
View File

@ -839,9 +839,11 @@ BinaryContext::getOrCreateJumpTable(BinaryFunction &Function, uint64_t Address,
assert(Address == JT->getAddress() && "unexpected non-empty jump table");
// Prevent associating a jump table to a specific fragment twice.
// This simple check arises from the assumption: no more than 2 fragments.
if (JT->Parents.size() == 1 && JT->Parents[0] != &Function) {
assert(areRelatedFragments(JT->Parents[0], &Function) &&
if (!llvm::is_contained(JT->Parents, &Function)) {
assert(llvm::all_of(JT->Parents,
[&](const BinaryFunction *BF) {
return areRelatedFragments(&Function, BF);
}) &&
"cannot re-use jump table of a different function");
// Duplicate the entry for the parent function for easy access
JT->Parents.push_back(&Function);
@ -852,8 +854,8 @@ BinaryContext::getOrCreateJumpTable(BinaryFunction &Function, uint64_t Address,
JT->print(this->outs());
}
Function.JumpTables.emplace(Address, JT);
JT->Parents[0]->setHasIndirectTargetToSplitFragment(true);
JT->Parents[1]->setHasIndirectTargetToSplitFragment(true);
for (BinaryFunction *Parent : JT->Parents)
Parent->setHasIndirectTargetToSplitFragment(true);
}
bool IsJumpTableParent = false;

95
bolt/test/X86/three-way-split-jt.s Normal file
View File

@ -0,0 +1,95 @@
## This reproduces an issue where the function is split into three fragments
## and all fragments access the same jump table.
# REQUIRES: system-linux
# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
# RUN: llvm-strip --strip-unneeded %t.o
# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q
# RUN: llvm-bolt %t.exe -o %t.out -v=1 -print-only=main.warm -print-cfg 2>&1 | FileCheck %s
# CHECK-DAG: BOLT-INFO: marking main.warm as a fragment of main
# CHECK-DAG: BOLT-INFO: marking main.cold as a fragment of main
# CHECK-DAG: BOLT-INFO: processing main.warm as a sibling of non-ignored function
# CHECK-DAG: BOLT-INFO: processing main.cold as a sibling of non-ignored function
# CHECK-DAG: BOLT-WARNING: Ignoring main.cold
# CHECK-DAG: BOLT-WARNING: Ignoring main.warm
# CHECK-DAG: BOLT-WARNING: Ignoring main
# CHECK: BOLT-WARNING: skipped 3 functions due to cold fragments
# CHECK: PIC Jump table JUMP_TABLE for function main, main.warm, main.cold
# CHECK-NEXT: 0x0000 : __ENTRY_main@0x[[#]]
# CHECK-NEXT: 0x0004 : __ENTRY_main@0x[[#]]
# CHECK-NEXT: 0x0008 : __ENTRY_main.cold@0x[[#]]
# CHECK-NEXT: 0x000c : __ENTRY_main@0x[[#]]
.globl main
.type main, %function
.p2align 2
main:
LBB0:
andl $0xf, %ecx
cmpb $0x4, %cl
## exit through ret
ja LBB3
## jump table dispatch, jumping to label indexed by val in %ecx
LBB1:
leaq JUMP_TABLE(%rip), %r8
movzbl %cl, %ecx
movslq (%r8,%rcx,4), %rax
addq %rax, %r8
jmpq *%r8
LBB2:
xorq %rax, %rax
LBB3:
addq $0x8, %rsp
ret
.size main, .-main
.globl main.warm
.type main.warm, %function
.p2align 2
main.warm:
LBB20:
andl $0xb, %ebx
cmpb $0x1, %cl
# exit through ret
ja LBB23
## jump table dispatch, jumping to label indexed by val in %ecx
LBB21:
leaq JUMP_TABLE(%rip), %r8
movzbl %cl, %ecx
movslq (%r8,%rcx,4), %rax
addq %rax, %r8
jmpq *%r8
LBB22:
xorq %rax, %rax
LBB23:
addq $0x8, %rsp
ret
.size main.warm, .-main.warm
## cold fragment is only reachable through jump table
.globl main.cold
.type main.cold, %function
main.cold:
leaq JUMP_TABLE(%rip), %r8
movzbl %cl, %ecx
movslq (%r8,%rcx,4), %rax
addq %rax, %r8
jmpq *%r8
LBB4:
callq abort
.size main.cold, .-main.cold
.rodata
## jmp table, entries must be R_X86_64_PC32 relocs
.globl JUMP_TABLE
JUMP_TABLE:
.long LBB2-JUMP_TABLE
.long LBB3-JUMP_TABLE
.long LBB4-JUMP_TABLE
.long LBB3-JUMP_TABLE