[llvm] [X86] Better handling of impossibly large stack frames (PR #124217)
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Thu Jan 23 17:59:36 PST 2025
https://github.com/mconst created https://github.com/llvm/llvm-project/pull/124217
If you try to create a stack frame of 4 GiB or larger with a 32-bit stack pointer, we currently emit invalid instructions like `mov eax, 5000000000` (unless you specify `-fstack-clash-protection`, in which case we emit a trap instead).
The trap seems nicer, so let's do that in all cases. This avoids emitting invalid instructions, and also fixes the "can't have 32-bit 16GB stack frame" assertion in `X86FrameLowering::emitSPUpdate()` (which used to be triggerable by user code, but is now correct).
This was originally part of #124041.
@phoebewang
>From 3ba96639099b778426050d1a1be01c794496a458 Mon Sep 17 00:00:00 2001
From: Michael Constant <mconst at gmail.com>
Date: Thu, 23 Jan 2025 02:04:33 -0800
Subject: [PATCH] [X86] Better handling of impossibly large stack frames
If you try to create a stack frame of 4 GiB or larger with a 32-bit
stack pointer, we currently emit invalid instructions like `mov eax,
5000000000` (unless you specify `-fstack-clash-protection`, in which
case we emit a trap instead).
The trap seems nicer, so let's do that in all cases. This avoids
emitting invalid instructions, and also fixes the "can't have 32-bit
16GB stack frame" assertion in `X86FrameLowering::emitSPUpdate()`
(which used to be triggerable by user code, but is now correct).
This was originally part of #124041.
---
llvm/lib/Target/X86/X86FrameLowering.cpp | 13 +++++++---
llvm/test/CodeGen/X86/huge-stack-offset.ll | 8 +++---
.../CodeGen/X86/stack-clash-extra-huge.ll | 26 ++-----------------
3 files changed, 14 insertions(+), 33 deletions(-)
diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index 47cc6a18ef84335..a7b60afb7f5473a 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -234,6 +234,14 @@ void X86FrameLowering::emitSPUpdate(MachineBasicBlock &MBB,
MachineInstr::MIFlag Flag =
isSub ? MachineInstr::FrameSetup : MachineInstr::FrameDestroy;
+ if (!Uses64BitFramePtr && !isUInt<32>(Offset)) {
+ // We're being asked to adjust a 32-bit stack pointer by 4 GiB or more.
+ // This might be unreachable code, so don't complain now; just trap if
+ // it's reached at runtime.
+ BuildMI(MBB, MBBI, DL, TII.get(X86::TRAP));
+ return;
+ }
+
uint64_t Chunk = (1LL << 31) - 1;
MachineFunction &MF = *MBB.getParent();
@@ -829,10 +837,7 @@ void X86FrameLowering::emitStackProbeInlineGenericLoop(
.addReg(StackPtr)
.setMIFlag(MachineInstr::FrameSetup);
} else {
- // We're being asked to probe a stack frame that's 4 GiB or larger,
- // but our stack pointer is only 32 bits. This might be unreachable
- // code, so don't complain now; just trap if it's reached at runtime.
- BuildMI(MBB, MBBI, DL, TII.get(X86::TRAP));
+ llvm_unreachable("Offset too large for 32-bit stack pointer");
}
// while in the loop, use loop-invariant reg for CFI,
diff --git a/llvm/test/CodeGen/X86/huge-stack-offset.ll b/llvm/test/CodeGen/X86/huge-stack-offset.ll
index e825328ccd89a25..6629811a59b23da 100644
--- a/llvm/test/CodeGen/X86/huge-stack-offset.ll
+++ b/llvm/test/CodeGen/X86/huge-stack-offset.ll
@@ -13,11 +13,9 @@ define void @foo() nounwind {
; CHECK-64-NEXT: addq [[RAX]], %rsp
; CHECK-32-LABEL: foo:
-; CHECK-32: movl $50000000{{..}}, %eax
-; CHECK-32-NEXT: subl %eax, %esp
+; CHECK-32: ud2
; CHECK-32-NOT: subl $2147483647, %esp
-; CHECK-32: movl $50000000{{..}}, [[EAX:%e..]]
-; CHECK-32-NEXT: addl [[EAX]], %esp
+; CHECK-32: ud2
%1 = alloca [5000000000 x i8], align 16
call void @bar(ptr %1)
ret void
@@ -46,7 +44,7 @@ define i32 @foo3(i32 inreg %x) nounwind {
; CHECK-64-NEXT: subq %rax, %rsp
; CHECK-32-LABEL: foo3:
-; CHECK-32: subl $2147483647, %esp
+; CHECK-32: ud2
; CHECK-32-NOT: movl ${{.*}}, %eax
%1 = alloca [5000000000 x i8], align 16
call void @bar(ptr %1)
diff --git a/llvm/test/CodeGen/X86/stack-clash-extra-huge.ll b/llvm/test/CodeGen/X86/stack-clash-extra-huge.ll
index b8031056fd6b0a7..d9b20f50e9a884a 100644
--- a/llvm/test/CodeGen/X86/stack-clash-extra-huge.ll
+++ b/llvm/test/CodeGen/X86/stack-clash-extra-huge.ll
@@ -30,44 +30,22 @@ define i32 @foo() local_unnamed_addr #0 {
; CHECK-X86-LABEL: foo:
; CHECK-X86: # %bb.0:
; CHECK-X86-NEXT: ud2
-; CHECK-X86-NEXT: .cfi_def_cfa_register %eax
-; CHECK-X86-NEXT: .cfi_adjust_cfa_offset 4800000000
-; CHECK-X86-NEXT: .LBB0_1: # =>This Inner Loop Header: Depth=1
-; CHECK-X86-NEXT: subl $4096, %esp # imm = 0x1000
-; CHECK-X86-NEXT: movl $0, (%esp)
-; CHECK-X86-NEXT: cmpl %eax, %esp
-; CHECK-X86-NEXT: jne .LBB0_1
-; CHECK-X86-NEXT: # %bb.2:
-; CHECK-X86-NEXT: subl $12, %esp
-; CHECK-X86-NEXT: .cfi_def_cfa_register %esp
; CHECK-X86-NEXT: .cfi_def_cfa_offset 4800000016
; CHECK-X86-NEXT: movl $1, 392(%esp)
; CHECK-X86-NEXT: movl $1, 28792(%esp)
; CHECK-X86-NEXT: movl (%esp), %eax
-; CHECK-X86-NEXT: movl $4800000012, %ecx # imm = 0x11E1A300C
-; CHECK-X86-NEXT: addl %ecx, %esp
+; CHECK-X86-NEXT: ud2
; CHECK-X86-NEXT: .cfi_def_cfa_offset 4
; CHECK-X86-NEXT: retl
;
; CHECK-X32-LABEL: foo:
; CHECK-X32: # %bb.0:
; CHECK-X32-NEXT: ud2
-; CHECK-X32-NEXT: .cfi_def_cfa_register %r11
-; CHECK-X32-NEXT: .cfi_adjust_cfa_offset 4799995904
-; CHECK-X32-NEXT: .LBB0_1: # =>This Inner Loop Header: Depth=1
-; CHECK-X32-NEXT: subl $4096, %esp # imm = 0x1000
-; CHECK-X32-NEXT: movq $0, (%esp)
-; CHECK-X32-NEXT: cmpl %r11d, %esp
-; CHECK-X32-NEXT: jne .LBB0_1
-; CHECK-X32-NEXT: # %bb.2:
-; CHECK-X32-NEXT: subl $3976, %esp # imm = 0xF88
-; CHECK-X32-NEXT: .cfi_def_cfa_register %rsp
; CHECK-X32-NEXT: .cfi_def_cfa_offset 4799999888
; CHECK-X32-NEXT: movl $1, 264(%esp)
; CHECK-X32-NEXT: movl $1, 28664(%esp)
; CHECK-X32-NEXT: movl -128(%esp), %eax
-; CHECK-X32-NEXT: movl $4799999880, %ecx # imm = 0x11E1A2F88
-; CHECK-X32-NEXT: addl %ecx, %esp
+; CHECK-X32-NEXT: ud2
; CHECK-X32-NEXT: .cfi_def_cfa_offset 8
; CHECK-X32-NEXT: retq
%a = alloca i32, i64 1200000000, align 16
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