[llvm] [llvm-exegesis] Add support for loading X86 segment registers (PR #76368)

[Clement Courbet via llvm-commits]

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@@ -924,38 +924,61 @@ void generateSyscall(long SyscallNumber, std::vector<MCInst> &GeneratedCode) {
   GeneratedCode.push_back(MCInstBuilder(X86::SYSCALL));
 }
 
+constexpr std::array<unsigned, 6> SyscallArgumentRegisters{
+    X86::RDI, X86::RSI, X86::RDX, X86::R10, X86::R8, X86::R9};
+
+static void saveSyscallRegisters(std::vector<MCInst> &GeneratedCode,
+                                 unsigned ArgumentCount) {
+  assert(ArgumentCount < 6 &&
+         "System calls only X86-64 Linux can only take six arguments");
+  // Preserve RCX and R11 (Clobbered by the system call).
+  generateRegisterStackPush(X86::RCX, GeneratedCode);
+  generateRegisterStackPush(X86::R11, GeneratedCode);
+  // Preserve RAX (used for the syscall number/return value).
+  generateRegisterStackPush(X86::RAX, GeneratedCode);
+  // Preserve the registers used to pass arguments to the system call.
+  for (unsigned I = 0; I < ArgumentCount; ++I)
+    generateRegisterStackPush(SyscallArgumentRegisters[I], GeneratedCode);
+}
+
+static void restoreSyscallRegisters(std::vector<MCInst> &GeneratedCode,
+                                    unsigned ArgumentCount) {
+  assert(ArgumentCount < 6 &&
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legrosbuffle wrote:

ditto

https://github.com/llvm/llvm-project/pull/76368