linux-user: Emulate /proc/cpuinfo output for riscv

RISC-V does not expose all extensions via hwcaps, thus some userspace
applications may want to query these via /proc/cpuinfo.

Currently when querying this file the host's file is shown instead
which is slightly confusing. Emulate a basic /proc/cpuinfo file
with mmu info and an ISA string.

Signed-off-by: Afonso Bordado <afonsobordado@gmail.com>
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Message-Id: <167873059442.9885.15152085316575248452-0@git.sr.ht>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/syscall.c

@@ -8231,7 +8231,8 @@ void target_exception_dump(CPUArchState *env, const char *fmt, int code)
 }
 
 #if HOST_BIG_ENDIAN != TARGET_BIG_ENDIAN || \
-    defined(TARGET_SPARC) || defined(TARGET_M68K) || defined(TARGET_HPPA)
+    defined(TARGET_SPARC) || defined(TARGET_M68K) || defined(TARGET_HPPA) || \
+    defined(TARGET_RISCV)
 static int is_proc(const char *filename, const char *entry)
 {
     return strcmp(filename, entry) == 0;
@@ -8309,6 +8310,35 @@ static int open_cpuinfo(CPUArchState *cpu_env, int fd)
 }
 #endif
 
+#if defined(TARGET_RISCV)
+static int open_cpuinfo(CPUArchState *cpu_env, int fd)
+{
+    int i;
+    int num_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+    RISCVCPU *cpu = env_archcpu(cpu_env);
+    const RISCVCPUConfig *cfg = riscv_cpu_cfg((CPURISCVState *) cpu_env);
+    char *isa_string = riscv_isa_string(cpu);
+    const char *mmu;
+
+    if (cfg->mmu) {
+        mmu = (cpu_env->xl == MXL_RV32) ? "sv32"  : "sv48";
+    } else {
+        mmu = "none";
+    }
+
+    for (i = 0; i < num_cpus; i++) {
+        dprintf(fd, "processor\t: %d\n", i);
+        dprintf(fd, "hart\t\t: %d\n", i);
+        dprintf(fd, "isa\t\t: %s\n", isa_string);
+        dprintf(fd, "mmu\t\t: %s\n", mmu);
+        dprintf(fd, "uarch\t\t: qemu\n\n");
+    }
+
+    g_free(isa_string);
+    return 0;
+}
+#endif
+
 #if defined(TARGET_M68K)
 static int open_hardware(CPUArchState *cpu_env, int fd)
 {
@@ -8333,7 +8363,7 @@ static int do_openat(CPUArchState *cpu_env, int dirfd, const char *pathname, int
 #if HOST_BIG_ENDIAN != TARGET_BIG_ENDIAN
         { "/proc/net/route", open_net_route, is_proc },
 #endif
-#if defined(TARGET_SPARC) || defined(TARGET_HPPA)
+#if defined(TARGET_SPARC) || defined(TARGET_HPPA) || defined(TARGET_RISCV)
         { "/proc/cpuinfo", open_cpuinfo, is_proc },
 #endif
 #if defined(TARGET_M68K)

tests/tcg/riscv64/Makefile.target

@@ -4,6 +4,7 @@
 VPATH += $(SRC_PATH)/tests/tcg/riscv64
 TESTS += test-div
 TESTS += noexec
+TESTS += cpuinfo
 
 # Disable compressed instructions for test-noc
 TESTS += test-noc

tests/tcg/riscv64/cpuinfo.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#define BUFFER_SIZE 1024
+
+int main(void)
+{
+    char buffer[BUFFER_SIZE];
+    FILE *fp = fopen("/proc/cpuinfo", "r");
+    assert(fp != NULL);
+
+    while (fgets(buffer, BUFFER_SIZE, fp) != NULL) {
+        if (strstr(buffer, "processor") != NULL) {
+            assert(strstr(buffer, "processor\t: ") == buffer);
+        } else if (strstr(buffer, "hart") != NULL) {
+            assert(strstr(buffer, "hart\t\t: ") == buffer);
+        } else if (strstr(buffer, "isa") != NULL) {
+            assert(strcmp(buffer, "isa\t\t: rv64imafdc_zicsr_zifencei\n") == 0);
+        } else if (strstr(buffer, "mmu") != NULL) {
+            assert(strcmp(buffer, "mmu\t\t: sv48\n") == 0);
+        } else if (strstr(buffer, "uarch") != NULL) {
+            assert(strcmp(buffer, "uarch\t\t: qemu\n") == 0);
+            break;
+        }
+    }
+
+    fclose(fp);
+    return 0;
+}