tcg/mips: detect available host instructions at runtime

Now that TCG supports enabling and disabling ops at runtime, it's
possible to detect the available host instructions at runtime, and
enable the corresponding ops accordingly.

Unfortunately it's not easy to probe for available instructions on
MIPS, the information is partially available in /proc/cpuinfo, and
not available in AUXV. This patch therefore probes for the instructions
by trying to execute them and by catching a possible SIGILL signal.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

2 files changed, 171 insertions, 92 deletions

diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
index 793532ec95..9b518c28f6 100644
--- a/tcg/mips/tcg-target.c
+++ b/tcg/mips/tcg-target.c
@@ -422,83 +422,83 @@ static inline void tcg_out_movi(TCGContext *s, TCGType type,
 
 static inline void tcg_out_bswap16(TCGContext *s, TCGReg ret, TCGReg arg)
 {
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
-    tcg_out_opc_reg(s, OPC_WSBH, ret, 0, arg);
-#else
-    /* ret and arg can't be register at */
-    if (ret == TCG_REG_AT || arg == TCG_REG_AT) {
-        tcg_abort();
-    }
+    if (use_mips32r2_instructions) {
+        tcg_out_opc_reg(s, OPC_WSBH, ret, 0, arg);
+    } else {
+        /* ret and arg can't be register at */
+        if (ret == TCG_REG_AT || arg == TCG_REG_AT) {
+            tcg_abort();
+        }
 
-    tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 8);
-    tcg_out_opc_sa(s, OPC_SLL, ret, arg, 8);
-    tcg_out_opc_imm(s, OPC_ANDI, ret, ret, 0xff00);
-    tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
-#endif
+        tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 8);
+        tcg_out_opc_sa(s, OPC_SLL, ret, arg, 8);
+        tcg_out_opc_imm(s, OPC_ANDI, ret, ret, 0xff00);
+        tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
+    }
 }
 
 static inline void tcg_out_bswap16s(TCGContext *s, TCGReg ret, TCGReg arg)
 {
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
-    tcg_out_opc_reg(s, OPC_WSBH, ret, 0, arg);
-    tcg_out_opc_reg(s, OPC_SEH, ret, 0, ret);
-#else
-    /* ret and arg can't be register at */
-    if (ret == TCG_REG_AT || arg == TCG_REG_AT) {
-        tcg_abort();
-    }
+    if (use_mips32r2_instructions) {
+        tcg_out_opc_reg(s, OPC_WSBH, ret, 0, arg);
+        tcg_out_opc_reg(s, OPC_SEH, ret, 0, ret);
+    } else {
+        /* ret and arg can't be register at */
+        if (ret == TCG_REG_AT || arg == TCG_REG_AT) {
+            tcg_abort();
+        }
 
-    tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 8);
-    tcg_out_opc_sa(s, OPC_SLL, ret, arg, 24);
-    tcg_out_opc_sa(s, OPC_SRA, ret, ret, 16);
-    tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
-#endif
+        tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 8);
+        tcg_out_opc_sa(s, OPC_SLL, ret, arg, 24);
+        tcg_out_opc_sa(s, OPC_SRA, ret, ret, 16);
+        tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
+    }
 }
 
 static inline void tcg_out_bswap32(TCGContext *s, TCGReg ret, TCGReg arg)
 {
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
-    tcg_out_opc_reg(s, OPC_WSBH, ret, 0, arg);
-    tcg_out_opc_sa(s, OPC_ROTR, ret, ret, 16);
-#else
-    /* ret and arg must be different and can't be register at */
-    if (ret == arg || ret == TCG_REG_AT || arg == TCG_REG_AT) {
-        tcg_abort();
-    }
+    if (use_mips32r2_instructions) {
+        tcg_out_opc_reg(s, OPC_WSBH, ret, 0, arg);
+        tcg_out_opc_sa(s, OPC_ROTR, ret, ret, 16);
+    } else {
+        /* ret and arg must be different and can't be register at */
+        if (ret == arg || ret == TCG_REG_AT || arg == TCG_REG_AT) {
+            tcg_abort();
+        }
 
-    tcg_out_opc_sa(s, OPC_SLL, ret, arg, 24);
+        tcg_out_opc_sa(s, OPC_SLL, ret, arg, 24);
 
-    tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 24);
-    tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
+        tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 24);
+        tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
 
-    tcg_out_opc_imm(s, OPC_ANDI, TCG_REG_AT, arg, 0xff00);
-    tcg_out_opc_sa(s, OPC_SLL, TCG_REG_AT, TCG_REG_AT, 8);
-    tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
+        tcg_out_opc_imm(s, OPC_ANDI, TCG_REG_AT, arg, 0xff00);
+        tcg_out_opc_sa(s, OPC_SLL, TCG_REG_AT, TCG_REG_AT, 8);
+        tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
 
-    tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 8);
-    tcg_out_opc_imm(s, OPC_ANDI, TCG_REG_AT, TCG_REG_AT, 0xff00);
-    tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
-#endif
+        tcg_out_opc_sa(s, OPC_SRL, TCG_REG_AT, arg, 8);
+        tcg_out_opc_imm(s, OPC_ANDI, TCG_REG_AT, TCG_REG_AT, 0xff00);
+        tcg_out_opc_reg(s, OPC_OR, ret, ret, TCG_REG_AT);
+    }
 }
 
 static inline void tcg_out_ext8s(TCGContext *s, TCGReg ret, TCGReg arg)
 {
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
-    tcg_out_opc_reg(s, OPC_SEB, ret, 0, arg);
-#else
-    tcg_out_opc_sa(s, OPC_SLL, ret, arg, 24);
-    tcg_out_opc_sa(s, OPC_SRA, ret, ret, 24);
-#endif
+    if (use_mips32r2_instructions) {
+        tcg_out_opc_reg(s, OPC_SEB, ret, 0, arg);
+    } else {
+        tcg_out_opc_sa(s, OPC_SLL, ret, arg, 24);
+        tcg_out_opc_sa(s, OPC_SRA, ret, ret, 24);
+    }
 }
 
 static inline void tcg_out_ext16s(TCGContext *s, TCGReg ret, TCGReg arg)
 {
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
-    tcg_out_opc_reg(s, OPC_SEH, ret, 0, arg);
-#else
-    tcg_out_opc_sa(s, OPC_SLL, ret, arg, 16);
-    tcg_out_opc_sa(s, OPC_SRA, ret, ret, 16);
-#endif
+    if (use_mips32r2_instructions) {
+        tcg_out_opc_reg(s, OPC_SEH, ret, 0, arg);
+    } else {
+        tcg_out_opc_sa(s, OPC_SLL, ret, arg, 16);
+        tcg_out_opc_sa(s, OPC_SRA, ret, ret, 16);
+    }
 }
 
 static inline void tcg_out_ldst(TCGContext *s, int opc, TCGArg arg,
@@ -1406,12 +1406,12 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
         tcg_out_mov(s, TCG_TYPE_I32, args[0], TCG_REG_AT);
         break;
     case INDEX_op_mul_i32:
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 1)
-        tcg_out_opc_reg(s, OPC_MUL, args[0], args[1], args[2]);
-#else
-        tcg_out_opc_reg(s, OPC_MULT, 0, args[1], args[2]);
-        tcg_out_opc_reg(s, OPC_MFLO, args[0], 0, 0);
-#endif
+        if (use_mips32_instructions) {
+            tcg_out_opc_reg(s, OPC_MUL, args[0], args[1], args[2]);
+        } else {
+            tcg_out_opc_reg(s, OPC_MULT, 0, args[1], args[2]);
+            tcg_out_opc_reg(s, OPC_MFLO, args[0], 0, 0);
+        }
         break;
     case INDEX_op_muls2_i32:
         tcg_out_opc_reg(s, OPC_MULT, 0, args[2], args[3]);
@@ -1617,29 +1617,19 @@ static const TCGTargetOpDef mips_op_defs[] = {
     { INDEX_op_shl_i32, { "r", "rZ", "ri" } },
     { INDEX_op_shr_i32, { "r", "rZ", "ri" } },
     { INDEX_op_sar_i32, { "r", "rZ", "ri" } },
-#if TCG_TARGET_HAS_rot_i32
     { INDEX_op_rotr_i32, { "r", "rZ", "ri" } },
     { INDEX_op_rotl_i32, { "r", "rZ", "ri" } },
-#endif
 
-#if TCG_TARGET_HAS_bswap16_i32
     { INDEX_op_bswap16_i32, { "r", "r" } },
-#endif
-#if TCG_TARGET_HAS_bswap32_i32
     { INDEX_op_bswap32_i32, { "r", "r" } },
-#endif
 
     { INDEX_op_ext8s_i32, { "r", "rZ" } },
     { INDEX_op_ext16s_i32, { "r", "rZ" } },
 
-#if TCG_TARGET_HAS_deposit_i32
     { INDEX_op_deposit_i32, { "r", "0", "rZ" } },
-#endif
 
     { INDEX_op_brcond_i32, { "rZ", "rZ" } },
-#if TCG_TARGET_HAS_movcond_i32
     { INDEX_op_movcond_i32, { "r", "rZ", "rZ", "rZ", "0" } },
-#endif
     { INDEX_op_setcond_i32, { "r", "rZ", "rZ" } },
     { INDEX_op_setcond2_i32, { "r", "rZ", "rZ", "rZ", "rZ" } },
 
@@ -1688,6 +1678,86 @@ static int tcg_target_callee_save_regs[] = {
     TCG_REG_RA,       /* should be last for ABI compliance */
 };
 
+/* The Linux kernel doesn't provide any information about the available
+   instruction set. Probe it using a signal handler. */
+
+#include <signal.h>
+
+#ifndef use_movnz_instructions
+bool use_movnz_instructions = false;
+#endif
+
+#ifndef use_mips32_instructions
+bool use_mips32_instructions = false;
+#endif
+
+#ifndef use_mips32r2_instructions
+bool use_mips32r2_instructions = false;
+#endif
+
+static volatile sig_atomic_t got_sigill;
+
+static void sigill_handler(int signo, siginfo_t *si, void *data)
+{
+    /* Skip the faulty instruction */
+    ucontext_t *uc = (ucontext_t *)data;
+    uc->uc_mcontext.pc += 4;
+
+    got_sigill = 1;
+}
+
+static void tcg_target_detect_isa(void)
+{
+    struct sigaction sa_old, sa_new;
+
+    memset(&sa_new, 0, sizeof(sa_new));
+    sa_new.sa_flags = SA_SIGINFO;
+    sa_new.sa_sigaction = sigill_handler;
+    sigaction(SIGILL, &sa_new, &sa_old);
+
+    /* Probe for movn/movz, necessary to implement movcond. */
+#ifndef use_movnz_instructions
+    got_sigill = 0;
+    asm volatile(".set push\n"
+                 ".set mips32\n"
+                 "movn $zero, $zero, $zero\n"
+                 "movz $zero, $zero, $zero\n"
+                 ".set pop\n"
+                 : : : );
+    use_movnz_instructions = !got_sigill;
+#endif
+
+    /* Probe for MIPS32 instructions. As no subsetting is allowed
+       by the specification, it is only necessary to probe for one
+       of the instructions. */
+#ifndef use_mips32_instructions
+    got_sigill = 0;
+    asm volatile(".set push\n"
+                 ".set mips32\n"
+                 "mul $zero, $zero\n"
+                 ".set pop\n"
+                 : : : );
+    use_mips32_instructions = !got_sigill;
+#endif
+
+    /* Probe for MIPS32r2 instructions if MIPS32 instructions are
+       available. As no subsetting is allowed by the specification,
+       it is only necessary to probe for one of the instructions. */
+#ifndef use_mips32r2_instructions
+    if (use_mips32_instructions) {
+        got_sigill = 0;
+        asm volatile(".set push\n"
+                     ".set mips32r2\n"
+                     "seb $zero, $zero\n"
+                     ".set pop\n"
+                     : : : );
+        use_mips32r2_instructions = !got_sigill;
+    }
+#endif
+
+    sigaction(SIGILL, &sa_old, NULL);
+}
+
 /* Generate global QEMU prologue and epilogue code */
 static void tcg_target_qemu_prologue(TCGContext *s)
 {
@@ -1727,6 +1797,7 @@ static void tcg_target_qemu_prologue(TCGContext *s)
 
 static void tcg_target_init(TCGContext *s)
 {
+    tcg_target_detect_isa();
     tcg_regset_set(tcg_target_available_regs[TCG_TYPE_I32], 0xffffffff);
     tcg_regset_set(tcg_target_call_clobber_regs,
                    (1 << TCG_REG_V0) |
diff --git a/tcg/mips/tcg-target.h b/tcg/mips/tcg-target.h
index a438950bc1..43072e3342 100644
--- a/tcg/mips/tcg-target.h
+++ b/tcg/mips/tcg-target.h
@@ -77,6 +77,29 @@ typedef enum {
 #define TCG_TARGET_CALL_STACK_OFFSET 16
 #define TCG_TARGET_CALL_ALIGN_ARGS 1
 
+/* MOVN/MOVZ instructions detection */
+#if (defined(__mips_isa_rev) && (__mips_isa_rev >= 1)) || \
+    defined(_MIPS_ARCH_LOONGSON2E) || defined(_MIPS_ARCH_LOONGSON2F) || \
+    defined(_MIPS_ARCH_MIPS4)
+#define use_movnz_instructions  1
+#else
+extern bool use_movnz_instructions;
+#endif
+
+/* MIPS32 instruction set detection */
+#if defined(__mips_isa_rev) && (__mips_isa_rev >= 1)
+#define use_mips32_instructions  1
+#else
+extern bool use_mips32_instructions;
+#endif
+
+/* MIPS32R2 instruction set detection */
+#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
+#define use_mips32r2_instructions  1
+#else
+extern bool use_mips32r2_instructions;
+#endif
+
 /* optional instructions */
 #define TCG_TARGET_HAS_div_i32          1
 #define TCG_TARGET_HAS_rem_i32          1
@@ -90,27 +113,12 @@ typedef enum {
 #define TCG_TARGET_HAS_nand_i32         0
 #define TCG_TARGET_HAS_muls2_i32        1
 
-/* optional instructions only implemented on MIPS4, MIPS32 and Loongson 2 */
-#if (defined(__mips_isa_rev) && (__mips_isa_rev >= 1)) || \
-    defined(_MIPS_ARCH_LOONGSON2E) || defined(_MIPS_ARCH_LOONGSON2F) || \
-    defined(_MIPS_ARCH_MIPS4)
-#define TCG_TARGET_HAS_movcond_i32      1
-#else
-#define TCG_TARGET_HAS_movcond_i32      0
-#endif
-
-/* optional instructions only implemented on MIPS32R2 */
-#if defined(__mips_isa_rev) && (__mips_isa_rev >= 2)
-#define TCG_TARGET_HAS_bswap16_i32      1
-#define TCG_TARGET_HAS_bswap32_i32      1
-#define TCG_TARGET_HAS_rot_i32          1
-#define TCG_TARGET_HAS_deposit_i32      1
-#else
-#define TCG_TARGET_HAS_bswap16_i32      0
-#define TCG_TARGET_HAS_bswap32_i32      0
-#define TCG_TARGET_HAS_rot_i32          0
-#define TCG_TARGET_HAS_deposit_i32      0
-#endif
+/* optional instructions detected at runtime */
+#define TCG_TARGET_HAS_movcond_i32      use_movnz_instructions
+#define TCG_TARGET_HAS_bswap16_i32      use_mips32r2_instructions
+#define TCG_TARGET_HAS_bswap32_i32      use_mips32r2_instructions
+#define TCG_TARGET_HAS_deposit_i32      use_mips32r2_instructions
+#define TCG_TARGET_HAS_rot_i32          use_mips32r2_instructions
 
 /* optional instructions automatically implemented */
 #define TCG_TARGET_HAS_neg_i32          0 /* sub  rd, zero, rt   */