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[Clang][BPF] Add __BPF_CPU_VERSION__ macro (llvm#71856)
Sometimes bpf developer might want to develop different codes based on particular cpu versioins. For example, cpu v1/v2/v3 branch target is 16bit while cpu v4 branch target is 32bit, thus cpu v4 allows more aggressive loop unrolling than cpu v1/v2/v3 (see [1] for a kernel selftest failure due to this). We would like to maintain aggressive loop unrolling for cpu v4 while limit loop unrolling for earlier cpu versions. Another example, signed divide also only available with cpu v4. Actually, adding cpu specific macros are fairly common in llvm. For example, x86 has maco like 'i486', '__pentium_mmx__', etc. AArch64 has '__ARM_NEON', '__ARM_FEATURE_SVE', etc. This patch added __BPF_CPU_VERSION__ macro. Current possible values are 0/1/2/3/4. The following are the -mcpu=... to __BPF_CPU_VERSION__ mapping: ``` cpu __BPF_CPU_VERSION__ no -mcpu=<...> 1 -mcpu=v1 1 -mcpu=v2 2 -mcpu=v3 3 -mcpu=v4 4 -mcpu=generic 1 -mcpu=probe 0 ``` This patch also added some macros for developers to identify some cpu insn features: ``` feature macro enabled in which cpu __BPF_FEATURE_JMP_EXT >= v2 __BPF_FEATURE_JMP32 >= v3 __BPF_FEATURE_ALU32 >= v3 __BPF_FEATURE_LDSX >= v4 __BPF_FEATURE_MOVSX >= v4 __BPF_FEATURE_BSWAP >= v4 __BPF_FEATURE_SDIV_SMOD >= v4 __BPF_FEATURE_GOTOL >= v4 __BPF_FEATURE_ST >= v4 ``` [1] https://lore.kernel.org/bpf/[email protected]/
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‎clang/lib/Basic/Targets/BPF.cpp

+31
Original file line numberDiff line numberDiff line change
@@ -29,6 +29,37 @@ void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
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MacroBuilder &Builder) const {
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Builder.defineMacro("__bpf__");
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Builder.defineMacro("__BPF__");
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std::string CPU = getTargetOpts().CPU;
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if (CPU == "probe") {
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Builder.defineMacro("__BPF_CPU_VERSION__", "0");
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return;
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}
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if (CPU.empty() || CPU == "generic" || CPU == "v1") {
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Builder.defineMacro("__BPF_CPU_VERSION__", "1");
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return;
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}
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std::string CpuVerNumStr = CPU.substr(1);
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Builder.defineMacro("__BPF_CPU_VERSION__", CpuVerNumStr);
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int CpuVerNum = std::stoi(CpuVerNumStr);
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if (CpuVerNum >= 2)
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Builder.defineMacro("__BPF_FEATURE_JMP_EXT");
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if (CpuVerNum >= 3) {
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Builder.defineMacro("__BPF_FEATURE_JMP32");
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Builder.defineMacro("__BPF_FEATURE_ALU32");
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}
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if (CpuVerNum >= 4) {
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Builder.defineMacro("__BPF_FEATURE_LDSX");
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Builder.defineMacro("__BPF_FEATURE_MOVSX");
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Builder.defineMacro("__BPF_FEATURE_BSWAP");
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Builder.defineMacro("__BPF_FEATURE_SDIV_SMOD");
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Builder.defineMacro("__BPF_FEATURE_GOTOL");
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Builder.defineMacro("__BPF_FEATURE_ST");
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}
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}
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static constexpr llvm::StringLiteral ValidCPUNames[] = {"generic", "v1", "v2",

‎clang/test/Preprocessor/bpf-predefined-macros.c

+81-2
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,11 @@
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// RUN: %clang -E -target bpfel -x c -o - %s | FileCheck %s
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// RUN: %clang -E -target bpfeb -x c -o - %s | FileCheck %s
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// RUN: %clang -E -target bpfel -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_NO %s
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// RUN: %clang -E -target bpfeb -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_NO %s
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// RUN: %clang -E -target bpfel -mcpu=v1 -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_V1 %s
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// RUN: %clang -E -target bpfel -mcpu=v2 -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_V2 %s
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// RUN: %clang -E -target bpfel -mcpu=v3 -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_V3 %s
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// RUN: %clang -E -target bpfel -mcpu=v4 -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_V4 %s
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// RUN: %clang -E -target bpfel -mcpu=generic -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_GENERIC %s
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// RUN: %clang -E -target bpfel -mcpu=probe -x c -o - %s | FileCheck -check-prefix=CHECK -check-prefix=CPU_PROBE %s
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#ifdef __bpf__
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int b;
@@ -10,7 +16,80 @@ int c;
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#ifdef bpf
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int d;
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#endif
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#ifdef __BPF_CPU_VERSION__
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int e;
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#endif
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#if __BPF_CPU_VERSION__ == 0
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int f;
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#endif
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#if __BPF_CPU_VERSION__ == 1
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int g;
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#endif
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#if __BPF_CPU_VERSION__ == 2
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int h;
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#endif
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#if __BPF_CPU_VERSION__ == 3
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int i;
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#endif
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#if __BPF_CPU_VERSION__ == 4
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int j;
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#endif
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#ifdef __BPF_FEATURE_JMP_EXT
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int k;
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#endif
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#ifdef __BPF_FEATURE_JMP32
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int l;
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#endif
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#ifdef __BPF_FEATURE_ALU32
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int m;
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#endif
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#ifdef __BPF_FEATURE_LDSX
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int n;
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#endif
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#ifdef __BPF_FEATURE_MOVSX
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int o;
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#endif
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#ifdef __BPF_FEATURE_BSWAP
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int p;
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#endif
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#ifdef __BPF_FEATURE_SDIV_SMOD
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int q;
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#endif
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#ifdef __BPF_FEATURE_GOTOL
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int r;
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#endif
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#ifdef __BPF_FEATURE_ST
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int s;
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#endif
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// CHECK: int b;
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// CHECK: int c;
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// CHECK-NOT: int d;
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// CHECK: int e;
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// CPU_NO: int g;
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// CPU_V1: int g;
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// CPU_V2: int h;
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// CPU_V2: int k;
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// CPU_V3: int i;
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// CPU_V3: int k;
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// CPU_V3: int l;
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// CPU_V3: int m;
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// CPU_V4: int j;
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// CPU_V4: int k;
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// CPU_V4: int l;
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// CPU_V4: int m;
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// CPU_V4: int n;
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// CPU_V4: int o;
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// CPU_V4: int p;
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// CPU_V4: int q;
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// CPU_V4: int r;
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// CPU_V4: int s;
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// CPU_GENERIC: int g;
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// CPU_PROBE: int f;

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