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[BOLT] Skip optimization of functions with alt instructions #95172

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Merged
merged 1 commit into from
Jun 18, 2024
Merged

[BOLT] Skip optimization of functions with alt instructions #95172

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16 changes: 7 additions & 9 deletions bolt/lib/Rewrite/LinuxKernelRewriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -273,9 +273,9 @@ class LinuxKernelRewriter final : public MetadataRewriter {

/// Handle alternative instruction info from .altinstructions.
Error readAltInstructions();
void processAltInstructionsPostCFG();
Error tryReadAltInstructions(uint32_t AltInstFeatureSize,
bool AltInstHasPadLen, bool ParseOnly);
Error rewriteAltInstructions();

/// Read .pci_fixup
Error readPCIFixupTable();
Expand Down Expand Up @@ -326,6 +326,8 @@ class LinuxKernelRewriter final : public MetadataRewriter {
if (Error E = processORCPostCFG())
return E;

processAltInstructionsPostCFG();

return Error::success();
}

Expand All @@ -335,9 +337,6 @@ class LinuxKernelRewriter final : public MetadataRewriter {
if (Error E = rewriteExceptionTable())
return E;

if (Error E = rewriteAltInstructions())
return E;

if (Error E = rewriteParaInstructions())
return E;

Expand Down Expand Up @@ -1485,12 +1484,11 @@ Error LinuxKernelRewriter::tryReadAltInstructions(uint32_t AltInstFeatureSize,
return Error::success();
}

Error LinuxKernelRewriter::rewriteAltInstructions() {
// Disable output of functions with alt instructions before the rewrite
// support is complete.
void LinuxKernelRewriter::processAltInstructionsPostCFG() {
// Disable optimization and output of functions with alt instructions before
// the rewrite support is complete. Alt instructions can modify the control
// flow, hence we may end up deleting seemingly unreachable code.
skipFunctionsWithAnnotation("AltInst");

return Error::success();
}

/// When the Linux kernel needs to handle an error associated with a given PCI
Expand Down
12 changes: 6 additions & 6 deletions bolt/test/X86/linux-alt-instruction.s
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Expand Up @@ -6,7 +6,7 @@
# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
# RUN: %clang %cflags -nostdlib %t.o -o %t.exe \
# RUN: -Wl,--image-base=0xffffffff80000000,--no-dynamic-linker,--no-eh-frame-hdr,--no-pie
# RUN: llvm-bolt %t.exe --print-normalized --alt-inst-feature-size=2 -o %t.out \
# RUN: llvm-bolt %t.exe --print-cfg --alt-inst-feature-size=2 -o %t.out \
# RUN: | FileCheck %s

## Older kernels used to have padlen field in alt_instr. Check compatibility.
Expand All @@ -15,7 +15,7 @@
# RUN: %s -o %t.padlen.o
# RUN: %clang %cflags -nostdlib %t.padlen.o -o %t.padlen.exe \
# RUN: -Wl,--image-base=0xffffffff80000000,--no-dynamic-linker,--no-eh-frame-hdr,--no-pie
# RUN: llvm-bolt %t.padlen.exe --print-normalized --alt-inst-has-padlen -o %t.padlen.out \
# RUN: llvm-bolt %t.padlen.exe --print-cfg --alt-inst-has-padlen -o %t.padlen.out \
# RUN: | FileCheck %s

## Check with a larger size of "feature" field in alt_instr.
Expand All @@ -24,7 +24,7 @@
# RUN: --defsym FEATURE_SIZE_4=1 %s -o %t.fs4.o
# RUN: %clang %cflags -nostdlib %t.fs4.o -o %t.fs4.exe \
# RUN: -Wl,--image-base=0xffffffff80000000,--no-dynamic-linker,--no-eh-frame-hdr,--no-pie
# RUN: llvm-bolt %t.fs4.exe --print-normalized --alt-inst-feature-size=4 -o %t.fs4.out \
# RUN: llvm-bolt %t.fs4.exe --print-cfg --alt-inst-feature-size=4 -o %t.fs4.out \
# RUN: | FileCheck %s

## Check that out-of-bounds read is handled properly.
Expand All @@ -33,9 +33,9 @@

## Check that BOLT automatically detects structure fields in .altinstructions.

# RUN: llvm-bolt %t.exe --print-normalized -o %t.out | FileCheck %s
# RUN: llvm-bolt %t.exe --print-normalized -o %t.padlen.out | FileCheck %s
# RUN: llvm-bolt %t.exe --print-normalized -o %t.fs4.out | FileCheck %s
# RUN: llvm-bolt %t.exe --print-cfg -o %t.out | FileCheck %s
# RUN: llvm-bolt %t.exe --print-cfg -o %t.padlen.out | FileCheck %s
# RUN: llvm-bolt %t.exe --print-cfg -o %t.fs4.out | FileCheck %s

# CHECK: BOLT-INFO: Linux kernel binary detected
# CHECK: BOLT-INFO: parsed 2 alternative instruction entries
Expand Down
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