https://github.com/yonghong-song created
https://github.com/llvm/llvm-project/pull/85358
Alexei added may_goto insn in [1]. The asm syntax for may_goto looks like
may_goto
The instruction represents a conditional branch but the condition is implicit.
Later in bpf kernel verifier, the 'may_goto ' insn will be rewritten
with an explicit condition. The encoding of 'may_goto' insn is enforced in [2]
and is also implemented in this patch.
In [3], 'may_goto' insn is encoded with raw bytes. I made the following change
```
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -328,10 +328,7 @@ l_true:
\
#define cond_break \
({ __label__ l_break, l_continue; \
-asm volatile goto("1:.byte 0xe5; \
- .byte 0; \
- .long ((%l[l_break] - 1b - 8) / 8) & 0x; \
- .short 0" \
+asm volatile goto("may_goto %l[l_break]" \
l_break);\
goto l_continue;\
l_break: break;
```
and ran the selftest with the latest llvm with this patch. All tests are passed.
[1]
https://lore.kernel.org/bpf/20240306031929.42666-1-alexei.starovoi...@gmail.com/
[2]
https://lore.kernel.org/bpf/20240306031929.42666-2-alexei.starovoi...@gmail.com/
[3]
https://lore.kernel.org/bpf/20240306031929.42666-4-alexei.starovoi...@gmail.com/
>From 98e0602539ecc28055e55f2f9ce1c3f7f9e8ddb2 Mon Sep 17 00:00:00 2001
From: Yonghong Song
Date: Thu, 14 Mar 2024 19:53:35 -0700
Subject: [PATCH] [BPF] Add support for may_goto insn
Alexei added may_goto insn in [1]. The asm syntax for may_goto looks like
may_goto
The instruction represents a conditional branch but the condition is implicit.
Later in bpf kernel verifier, the 'may_goto ' insn will be rewritten
with an explicit condition. The encoding of 'may_goto' insn is enforced
in [2] and is also implemented in this patch.
In [3], 'may_goto' insn is encoded with raw bytes. I made the following change
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -328,10 +328,7 @@ l_true:
\
#define cond_break \
({ __label__ l_break, l_continue; \
-asm volatile goto("1:.byte 0xe5; \
- .byte 0; \
- .long ((%l[l_break] - 1b - 8) / 8) & 0x; \
- .short 0" \
+asm volatile goto("may_goto %l[l_break]" \
l_break);\
goto l_continue;\
l_break: break;
and ran the selftest with the latest llvm with this patch. All tests are passed.
[1]
https://lore.kernel.org/bpf/20240306031929.42666-1-alexei.starovoi...@gmail.com/
[2]
https://lore.kernel.org/bpf/20240306031929.42666-2-alexei.starovoi...@gmail.com/
[3]
https://lore.kernel.org/bpf/20240306031929.42666-4-alexei.starovoi...@gmail.com/
Signed-off-by: Yonghong Song
---
clang/lib/Basic/Targets/BPF.cpp | 1 +
llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp | 1 +
llvm/lib/Target/BPF/BPFInstrFormats.td | 1 +
llvm/lib/Target/BPF/BPFInstrInfo.td | 13 +
.../lib/Target/BPF/MCTargetDesc/BPFMCTargetDesc.cpp | 5 -
llvm/test/MC/BPF/insn-unit.s| 2 ++
6 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/clang/lib/Basic/Targets/BPF.cpp b/clang/lib/Basic/Targets/BPF.cpp
index a90398a362d10a..b5ba11a3bdca9d 100644
--- a/clang/lib/Basic/Targets/BPF.cpp
+++ b/clang/lib/Basic/Targets/BPF.cpp
@@ -45,6 +45,7 @@ void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
std::string CpuVerNumStr = CPU.substr(1);
Builder.defineMacro("__BPF_CPU_VERSION__", CpuVerNumStr);
+ Builder.defineMacro("__BPF_FEATURE_MAY_GOTO");
int CpuVerNum = std::stoi(CpuVerNumStr);
if (CpuVerNum >= 2)
diff --git a/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
b/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
index 3145bc3d19f5dc..1688355f427cc7 100644
--- a/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
+++ b/llvm/lib/Target/BPF/AsmParser/BPFAsmParser.cpp
@@ -232,6 +232,7 @@ struct BPFOperand : public MCParsedAsmOperand {
.Case("callx", true)
.Case("goto", true)
.Case("gotol", true)
+.Case("may_goto", true)
.Case("*", true)
.Case("exit", true)
.Case("lock", tru
