libjvmti.c

Go to the documentation of this file.

// SPDX-License-Identifier: GPL-2.0
#include <linux/compiler.h>
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <err.h>
#include <jvmti.h>
#include <jvmticmlr.h>
#include <limits.h>

#include "jvmti_agent.h"

static int has_line_numbers;
void *jvmti_agent;

static void print_error(jvmtiEnv *jvmti, const char *msg, jvmtiError ret)
{
    char *err_msg = NULL;
    jvmtiError err;
    err = (*jvmti)->GetErrorName(jvmti, ret, &err_msg);
    if (err == JVMTI_ERROR_NONE) {
        warnx("%s failed with %s", msg, err_msg);
        (*jvmti)->Deallocate(jvmti, (unsigned char *)err_msg);
    } else {
        warnx("%s failed with an unknown error %d", msg, ret);
    }
}

static jvmtiError
do_get_line_numbers(jvmtiEnv *jvmti, void *pc, jmethodID m, jint bci,
            jvmti_line_info_t *tab, jint *nr)
{
    jint i, lines = 0;
    jint nr_lines = 0;
    jvmtiLineNumberEntry *loc_tab = NULL;
    jvmtiError ret;

    ret = (*jvmti)->GetLineNumberTable(jvmti, m, &nr_lines, &loc_tab);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetLineNumberTable", ret);
        return ret;
    }

    for (i = 0; i < nr_lines; i++) {
        if (loc_tab[i].start_location < bci) {
            tab[lines].pc = (unsigned long)pc;
            tab[lines].line_number = loc_tab[i].line_number;
            tab[lines].discrim = 0; /* not yet used */
            tab[lines].methodID = m;
            lines++;
        } else {
            break;
        }
    }
    (*jvmti)->Deallocate(jvmti, (unsigned char *)loc_tab);
    *nr = lines;
    return JVMTI_ERROR_NONE;
}

static jvmtiError
get_line_numbers(jvmtiEnv *jvmti, const void *compile_info, jvmti_line_info_t **tab, int *nr_lines)
{
    const jvmtiCompiledMethodLoadRecordHeader *hdr;
    jvmtiCompiledMethodLoadInlineRecord *rec;
    jvmtiLineNumberEntry *lne = NULL;
    PCStackInfo *c;
    jint nr, ret;
    int nr_total = 0;
    int i, lines_total = 0;

    if (!(tab && nr_lines))
        return JVMTI_ERROR_NULL_POINTER;

    /*
     * Phase 1 -- get the number of lines necessary
     */
    for (hdr = compile_info; hdr != NULL; hdr = hdr->next) {
        if (hdr->kind == JVMTI_CMLR_INLINE_INFO) {
            rec = (jvmtiCompiledMethodLoadInlineRecord *)hdr;
            for (i = 0; i < rec->numpcs; i++) {
                c = rec->pcinfo + i;
                nr = 0;
                /*
                 * unfortunately, need a tab to get the number of lines!
                 */
                ret = (*jvmti)->GetLineNumberTable(jvmti, c->methods[0], &nr, &lne);
                if (ret == JVMTI_ERROR_NONE) {
                    /* free what was allocated for nothing */
                    (*jvmti)->Deallocate(jvmti, (unsigned char *)lne);
                    nr_total += (int)nr;
                } else {
                    print_error(jvmti, "GetLineNumberTable", ret);
                }
            }
        }
    }

    if (nr_total == 0)
        return JVMTI_ERROR_NOT_FOUND;

    /*
     * Phase 2 -- allocate big enough line table
     */
    *tab = malloc(nr_total * sizeof(**tab));
    if (!*tab)
        return JVMTI_ERROR_OUT_OF_MEMORY;

    for (hdr = compile_info; hdr != NULL; hdr = hdr->next) {
        if (hdr->kind == JVMTI_CMLR_INLINE_INFO) {
            rec = (jvmtiCompiledMethodLoadInlineRecord *)hdr;
            for (i = 0; i < rec->numpcs; i++) {
                c = rec->pcinfo + i;
                nr = 0;
                ret = do_get_line_numbers(jvmti, c->pc,
                              c->methods[0],
                              c->bcis[0],
                              *tab + lines_total,
                              &nr);
                if (ret == JVMTI_ERROR_NONE)
                    lines_total += nr;
            }
        }
    }
    *nr_lines = lines_total;
    return JVMTI_ERROR_NONE;
}

static void
copy_class_filename(const char * class_sign, const char * file_name, char * result, size_t max_length)
{
    /*
    * Assume path name is class hierarchy, this is a common practice with Java programs
    */
    if (*class_sign == 'L') {
        int j, i = 0;
        char *p = strrchr(class_sign, '/');
        if (p) {
            /* drop the 'L' prefix and copy up to the final '/' */
            for (i = 0; i < (p - class_sign); i++)
                result[i] = class_sign[i+1];
        }
        /*
        * append file name, we use loops and not string ops to avoid modifying
        * class_sign which is used later for the symbol name
        */
        for (j = 0; i < (max_length - 1) && file_name && j < strlen(file_name); j++, i++)
            result[i] = file_name[j];

        result[i] = '\0';
    } else {
        /* fallback case */
        size_t file_name_len = strlen(file_name);
        strncpy(result, file_name, file_name_len < max_length ? file_name_len : max_length);
    }
}

static jvmtiError
get_source_filename(jvmtiEnv *jvmti, jmethodID methodID, char ** buffer)
{
    jvmtiError ret;
    jclass decl_class;
    char *file_name = NULL;
    char *class_sign = NULL;
    char fn[PATH_MAX];
    size_t len;

    ret = (*jvmti)->GetMethodDeclaringClass(jvmti, methodID, &decl_class);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetMethodDeclaringClass", ret);
        return ret;
    }

    ret = (*jvmti)->GetSourceFileName(jvmti, decl_class, &file_name);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetSourceFileName", ret);
        return ret;
    }

    ret = (*jvmti)->GetClassSignature(jvmti, decl_class, &class_sign, NULL);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetClassSignature", ret);
        goto free_file_name_error;
    }

    copy_class_filename(class_sign, file_name, fn, PATH_MAX);
    len = strlen(fn);
    *buffer = malloc((len + 1) * sizeof(char));
    if (!*buffer) {
        print_error(jvmti, "GetClassSignature", ret);
        ret = JVMTI_ERROR_OUT_OF_MEMORY;
        goto free_class_sign_error;
    }
    strcpy(*buffer, fn);
    ret = JVMTI_ERROR_NONE;

free_class_sign_error:
    (*jvmti)->Deallocate(jvmti, (unsigned char *)class_sign);
free_file_name_error:
    (*jvmti)->Deallocate(jvmti, (unsigned char *)file_name);

    return ret;
}

static jvmtiError
fill_source_filenames(jvmtiEnv *jvmti, int nr_lines,
              const jvmti_line_info_t * line_tab,
              char ** file_names)
{
    int index;
    jvmtiError ret;

    for (index = 0; index < nr_lines; ++index) {
        ret = get_source_filename(jvmti, line_tab[index].methodID, &(file_names[index]));
        if (ret != JVMTI_ERROR_NONE)
            return ret;
    }

    return JVMTI_ERROR_NONE;
}

static void JNICALL
compiled_method_load_cb(jvmtiEnv *jvmti,
            jmethodID method,
            jint code_size,
            void const *code_addr,
            jint map_length,
            jvmtiAddrLocationMap const *map,
            const void *compile_info)
{
    jvmti_line_info_t *line_tab = NULL;
    char ** line_file_names = NULL;
    jclass decl_class;
    char *class_sign = NULL;
    char *func_name = NULL;
    char *func_sign = NULL;
    char *file_name = NULL;
    char fn[PATH_MAX];
    uint64_t addr = (uint64_t)(uintptr_t)code_addr;
    jvmtiError ret;
    int nr_lines = 0; /* in line_tab[] */
    size_t len;
    int output_debug_info = 0;

    ret = (*jvmti)->GetMethodDeclaringClass(jvmti, method,
                        &decl_class);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetMethodDeclaringClass", ret);
        return;
    }

    if (has_line_numbers && map && map_length) {
        ret = get_line_numbers(jvmti, compile_info, &line_tab, &nr_lines);
        if (ret != JVMTI_ERROR_NONE) {
            warnx("jvmti: cannot get line table for method");
            nr_lines = 0;
        } else if (nr_lines > 0) {
            line_file_names = malloc(sizeof(char*) * nr_lines);
            if (!line_file_names) {
                warnx("jvmti: cannot allocate space for line table method names");
            } else {
                memset(line_file_names, 0, sizeof(char*) * nr_lines);
                ret = fill_source_filenames(jvmti, nr_lines, line_tab, line_file_names);
                if (ret != JVMTI_ERROR_NONE) {
                    warnx("jvmti: fill_source_filenames failed");
                } else {
                    output_debug_info = 1;
                }
            }
        }
    }

    ret = (*jvmti)->GetSourceFileName(jvmti, decl_class, &file_name);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetSourceFileName", ret);
        goto error;
    }

    ret = (*jvmti)->GetClassSignature(jvmti, decl_class,
                      &class_sign, NULL);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetClassSignature", ret);
        goto error;
    }

    ret = (*jvmti)->GetMethodName(jvmti, method, &func_name,
                      &func_sign, NULL);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "GetMethodName", ret);
        goto error;
    }

    copy_class_filename(class_sign, file_name, fn, PATH_MAX);

    /*
     * write source line info record if we have it
     */
    if (output_debug_info)
        if (jvmti_write_debug_info(jvmti_agent, addr, nr_lines, line_tab, (const char * const *) line_file_names))
            warnx("jvmti: write_debug_info() failed");

    len = strlen(func_name) + strlen(class_sign) + strlen(func_sign) + 2;
    {
        char str[len];
        snprintf(str, len, "%s%s%s", class_sign, func_name, func_sign);

        if (jvmti_write_code(jvmti_agent, str, addr, code_addr, code_size))
            warnx("jvmti: write_code() failed");
    }
error:
    (*jvmti)->Deallocate(jvmti, (unsigned char *)func_name);
    (*jvmti)->Deallocate(jvmti, (unsigned char *)func_sign);
    (*jvmti)->Deallocate(jvmti, (unsigned char *)class_sign);
    (*jvmti)->Deallocate(jvmti, (unsigned char *)file_name);
    free(line_tab);
    while (line_file_names && (nr_lines > 0)) {
        if (line_file_names[nr_lines - 1]) {
            free(line_file_names[nr_lines - 1]);
        }
        nr_lines -= 1;
    }
    free(line_file_names);
}

static void JNICALL
code_generated_cb(jvmtiEnv *jvmti,
          char const *name,
          void const *code_addr,
          jint code_size)
{
    uint64_t addr = (uint64_t)(unsigned long)code_addr;
    int ret;

    ret = jvmti_write_code(jvmti_agent, name, addr, code_addr, code_size);
    if (ret)
        warnx("jvmti: write_code() failed for code_generated");
}

JNIEXPORT jint JNICALL
Agent_OnLoad(JavaVM *jvm, char *options, void *reserved __maybe_unused)
{
    jvmtiEventCallbacks cb;
    jvmtiCapabilities caps1;
    jvmtiJlocationFormat format;
    jvmtiEnv *jvmti = NULL;
    jint ret;

    jvmti_agent = jvmti_open();
    if (!jvmti_agent) {
        warnx("jvmti: open_agent failed");
        return -1;
    }

    /*
     * Request a JVMTI interface version 1 environment
     */
    ret = (*jvm)->GetEnv(jvm, (void *)&jvmti, JVMTI_VERSION_1);
    if (ret != JNI_OK) {
        warnx("jvmti: jvmti version 1 not supported");
        return -1;
    }

    /*
     * acquire method_load capability, we require it
     * request line numbers (optional)
     */
    memset(&caps1, 0, sizeof(caps1));
    caps1.can_generate_compiled_method_load_events = 1;

    ret = (*jvmti)->AddCapabilities(jvmti, &caps1);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "AddCapabilities", ret);
        return -1;
    }
    ret = (*jvmti)->GetJLocationFormat(jvmti, &format);
        if (ret == JVMTI_ERROR_NONE && format == JVMTI_JLOCATION_JVMBCI) {
                memset(&caps1, 0, sizeof(caps1));
                caps1.can_get_line_numbers = 1;
                caps1.can_get_source_file_name = 1;
        ret = (*jvmti)->AddCapabilities(jvmti, &caps1);
                if (ret == JVMTI_ERROR_NONE)
                        has_line_numbers = 1;
        } else if (ret != JVMTI_ERROR_NONE)
        print_error(jvmti, "GetJLocationFormat", ret);


    memset(&cb, 0, sizeof(cb));

    cb.CompiledMethodLoad   = compiled_method_load_cb;
    cb.DynamicCodeGenerated = code_generated_cb;

    ret = (*jvmti)->SetEventCallbacks(jvmti, &cb, sizeof(cb));
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "SetEventCallbacks", ret);
        return -1;
    }

    ret = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
            JVMTI_EVENT_COMPILED_METHOD_LOAD, NULL);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "SetEventNotificationMode(METHOD_LOAD)", ret);
        return -1;
    }

    ret = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
            JVMTI_EVENT_DYNAMIC_CODE_GENERATED, NULL);
    if (ret != JVMTI_ERROR_NONE) {
        print_error(jvmti, "SetEventNotificationMode(CODE_GENERATED)", ret);
        return -1;
    }
    return 0;
}

JNIEXPORT void JNICALL
Agent_OnUnload(JavaVM *jvm __maybe_unused)
{
    int ret;

    ret = jvmti_close(jvmti_agent);
    if (ret)
        errx(1, "Error: op_close_agent()");
}