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[SFrames] Implement .cfi_restore, remember_state, and restore_state #159832

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Merged
Sterling-Augustine merged 2 commits into from
Sep 24, 2025
Merged

[SFrames] Implement .cfi_restore, remember_state, and restore_state #159832

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[SFrames] Implement .cfi_restore, .cfi_remember_state, and .cfi_resto…
Sterling-Augustine Sep 19, 2025
0c7cfe6
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Sterling-Augustine Sep 22, 2025
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29 changes: 24 additions & 5 deletions llvm/lib/MC/MCSFrame.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,8 @@ struct SFrameFDE {
MCFragment *Frag;
// Unwinding fres
SmallVector<SFrameFRE> FREs;
// .cfi_remember_state stack
SmallVector<SFrameFRE> SaveState;

SFrameFDE(const MCDwarfFrameInfo &DF, MCSymbol *FRES)
: DFrame(DF), FREStart(FRES), Frag(nullptr) {}
Expand Down Expand Up @@ -237,13 +239,30 @@ class SFrameEmitterImpl {
case MCCFIInstruction::OpAdjustCfaOffset:
return setCFAOffset(FRE, CFI.getLoc(), FRE.CFAOffset + CFI.getOffset());
case MCCFIInstruction::OpRememberState:
// TODO: Implement. Will use FDE.
if (FDE.FREs.size() == 1) {
// Error for gas compatibility: If the initial FRE isn't complete,
// then any state is incomplete. FIXME: Dwarf doesn't error here.
// Why should sframe?
Streamer.getContext().reportWarning(
CFI.getLoc(), "skipping SFrame FDE; .cfi_remember_state without "
"prior SFrame FRE state");
return false;
}
FDE.SaveState.push_back(FRE);
return true;
case MCCFIInstruction::OpRestore:
// TODO: Implement. Will use FDE.
// The first FRE generated has the original state.
if (CFI.getRegister() == FPReg)
FRE.FPOffset = FDE.FREs.front().FPOffset;
else if (CFI.getRegister() == RAReg)
FRE.RAOffset = FDE.FREs.front().RAOffset;
return true;
case MCCFIInstruction::OpRestoreState:
// TODO: Implement. Will use FDE.
// The cfi parser will have caught unbalanced directives earlier, so a
// mismatch here is an implementation error.
assert(!FDE.SaveState.empty() &&
"cfi_restore_state without cfi_save_state");
FRE = FDE.SaveState.pop_back_val();
return true;
case MCCFIInstruction::OpEscape:
// TODO: Implement. Will use FDE.
Expand Down Expand Up @@ -394,8 +413,8 @@ class SFrameEmitterImpl {
// shf_fdeoff. With no sfh_auxhdr, these immediately follow this header.
Streamer.emitInt32(0);
// shf_freoff
Streamer.emitAbsoluteSymbolDiff(FRESubSectionStart, FDESubSectionStart,
sizeof(uint32_t));
Streamer.emitInt32(FDEs.size() *
sizeof(sframe::FuncDescEntry<endianness::native>));
}

void emitFDEs() {
Expand Down
110 changes: 90 additions & 20 deletions llvm/test/MC/ELF/cfi-sframe-fre-cases.s
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ fde4_fre_offset_sizes:
# CHECK: FuncDescEntry [0] {
# CHECK: Start FRE Offset: 0
# CHECK: FRE Type: Addr1 (0x0)
.cfi_startproc
.cfi_startproc
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x0
# CHECK-NEXT: Return Address Signed: No
Expand All @@ -27,80 +27,80 @@ fde4_fre_offset_sizes:
# CHECK-NEXT: RA Offset: -8
.long 0
# Uninteresting register no new fre, no effect on cfa
.cfi_offset 0, 8
.cfi_offset 0, 8
.long 0
.cfi_def_cfa_offset 0x78
.cfi_def_cfa_offset 0x78
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x8
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B1 (0x0)
# CHECK-NEXT: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 120
# CHECK-NEXT: RA Offset: -8
.long 0
.long 0
# Uninteresting register no new fre, no effect on cfa
.cfi_rel_offset 1, 8
.long 0
.cfi_def_cfa_offset 0x80
.cfi_def_cfa_offset 0x80
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x10
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B2 (0x1)
# CHECK-NEXT: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 128
# CHECK-NEXT: RA Offset: -8
.long 0
.long 0
# Uninteresting register no new fre, no effect on cfa
.cfi_val_offset 1, 8
.long 0
.cfi_def_cfa_offset 0x7FFF
.cfi_def_cfa_offset 0x7FFF
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x18
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B2 (0x1)
# CHECK-NEXT: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 32767
# CHECK-NEXT: RA Offset: -8
.long 0
.cfi_def_cfa_offset 0x8000
.long 0
.cfi_def_cfa_offset 0x8000
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x1C
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B4 (0x2)
# CHECK-NEXT: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 32768
# CHECK-NEXT: RA Offset: -8
.long 0
.cfi_def_cfa_offset 0x8
.long 0
.cfi_def_cfa_offset 0x8
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x20
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B1 (0x0)
# CHECK-NEXT: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 8
# CHECK-NEXT: RA Offset: -8
.long 0
.cfi_adjust_cfa_offset 0x8
.long 0
.cfi_adjust_cfa_offset 0x8
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x24
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B1 (0x0)
# CHECK-NEXT: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 16
# CHECK-NEXT: RA Offset: -8
.long 0
.cfi_def_cfa_register 6 # switch to fp
.long 0
.cfi_def_cfa_register 6 # switch to fp
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x28
# CHECK-NEXT: Return Address Signed: No
# CHECK-NEXT: Offset Size: B1 (0x0)
# CHECK-NEXT: Base Register: FP (0x0)
# CHECK-NEXT: CFA Offset: 16
# CHECK-NEXT: RA Offset: -8
.long 0
.cfi_offset 7, 32
# sp not the cfa but with large offset still changes encoding.
.cfi_offset 6, 0x7FF8
.long 0
.cfi_offset 7, 32
# sp not the cfa but with large offset still changes encoding.
.cfi_offset 6, 0x7FF8
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x2C
# CHECK-NEXT: Return Address Signed: No
Expand All @@ -109,5 +109,75 @@ fde4_fre_offset_sizes:
# CHECK-NEXT: CFA Offset: 16
# CHECK-NEXT: RA Offset: -8
# CHECK-NEXT: FP Offset: 32760
.long 0
.long 0
.cfi_endproc

.align 1024
restore_reg:
# CHECK: FuncDescEntry [1] {
# CHECK: Start FRE Offset: 0x23
# CHECK-NEXT: Num FREs: 3
.cfi_startproc
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x400
# CHECK-NOT FP Offset{{.*}}
# CHECK: }
.long 0
.cfi_offset 6, 32
# CHECK Frame Row Entry {
# CHECK-NEXT Start Address: 0x404
# CHECK: FP Offset: 32
.long 0
.cfi_restore 6
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x408
# CHECK-NOT FP Offset{{.*}}
# CHECK: }
.long 0
.cfi_endproc

.align 1024
remember_restore_state:
# CHECK: FuncDescEntry [2] {
# CHECK: Start FRE Offset: 0x2D
# CHECK-NEXT: Num FREs: 4
.cfi_startproc
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x800
# CHECK-NOT FP Offset{{.*}}
# CHECK: }
.long 0
.cfi_offset 6, 8
.cfi_offset 7, 16
.cfi_offset 8, 24
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x804
# CHECK: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 8
# CHECK-NEXT: RA Offset: -8
# CHECK-NEXT: FP Offset: 8
# CHECK-NEXT: }
.long 0
.cfi_remember_state
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x808
# CHECK: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 8
# CHECK-NEXT: RA Offset: -8
# CHECK-NEXT: FP Offset: 32
# CHECK-NEXT: }
.cfi_offset 6, 32
.cfi_offset 7, 40
.cfi_offset 8, 48
.long 0
# CHECK: Frame Row Entry {
# CHECK-NEXT: Start Address: 0x80C
# CHECK: Base Register: SP (0x1)
# CHECK-NEXT: CFA Offset: 8
# CHECK-NEXT: RA Offset: -8
# CHECK-NEXT: FP Offset: 8
# CHECK-NEXT: }
.cfi_restore_state
.long 0

.cfi_endproc
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