cosmopolitan/libc/runtime/ftrace.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/alg/bisectcarleft.internal.h"
#include "libc/bits/bits.h"
#include "libc/bits/safemacros.h"
#include "libc/calls/calls.h"
#include "libc/calls/internal.h"
#include "libc/calls/struct/sigset.h"
#include "libc/dce.h"
#include "libc/intrin/repmovsb.h"
#include "libc/macros.h"
#include "libc/nexgen32e/stackframe.h"
#include "libc/nt/files.h"
#include "libc/nt/runtime.h"
#include "libc/nt/thunk/msabi.h"
#include "libc/runtime/internal.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/symbols.internal.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/fileno.h"
#include "libc/sysv/consts/nr.h"
#include "libc/sysv/consts/prot.h"
#include "libc/sysv/consts/sig.h"

/**
 * @fileoverview Plain-text function call logging.
 *
 * Able to log ~2 million function calls per second, which is mostly
 * bottlenecked by system call overhead. Log size is reasonable if piped
 * into gzip.
 */

void ftrace_hook(void);

static int noreentry;
static char g_buf[512];
static const char *g_lastsymbol;
static struct SymbolTable *g_symbols;

forceinline int GetNestingLevel(struct StackFrame *frame) {
  int nesting = -2;
  while (frame) {
    ++nesting;
    frame = frame->next;
  }
  return max(0, nesting);
}

/**
 * Prints name of function being called.
 *
 * We insert CALL instructions that point to this function, in the
 * prologues of other functions. We assume those functions behave
 * according to the System Five NexGen32e ABI.
 */
privileged void ftrace(void) {
  size_t i, j, nesting;
  const char *symbol;
  struct StackFrame *frame;
  if (!cmpxchg(&noreentry, 0, 1)) return;
  if (g_symbols) {
    frame = __builtin_frame_address(0);
    frame = frame->next;
    symbol =
        &g_symbols->name_base[g_symbols
                                  ->symbols[bisectcarleft(
                                      (const int32_t(*)[2])g_symbols->symbols,
                                      g_symbols->count,
                                      frame->addr - g_symbols->addr_base)]
                                  .name_rva];
    if (symbol != g_lastsymbol &&
        (nesting = GetNestingLevel(frame)) * 2 < ARRAYLEN(g_buf) - 4) {
      i = 2;
      j = 0;
      while (nesting--) {
        asm volatile("" : : : "memory");
        g_buf[i++] = ' ';
        g_buf[i++] = ' ';
      }
      while (i < ARRAYLEN(g_buf) - 2 && symbol[j]) {
        asm volatile("" : : : "memory");
        g_buf[i++] = symbol[j++];
      }
      g_buf[i++] = '\r';
      g_buf[i++] = '\n';
      write(2, g_buf, i);
    }
    g_lastsymbol = symbol;
  }
  noreentry = 0;
}

/**
 * Enables plaintext function tracing if `--ftrace` flag is passed.
 *
 * The `--ftrace` CLI arg is removed before main() is called. This code
 * is intended for diagnostic purposes and assumes binaries are
 * trustworthy and stack isn't corrupted. Logging plain text allows
 * program structure to easily be visualized and hotspots identified w/
 * `sed | sort | uniq -c | sort`. A compressed trace can be made by
 * appending `--ftrace 2>&1 | gzip -4 >trace.gz` to the CLI arguments.
 *
 * @see libc/runtime/_init.S for documentation
 */
textstartup int ftrace_init(int argc, char *argv[]) {
  int i;
  bool foundflag;
  foundflag = false;
  for (i = 1; i <= argc; ++i) {
    if (!foundflag) {
      if (argv[i]) {
        if (strcmp(argv[i], "--ftrace") == 0) {
          foundflag = true;
        } else if (strcmp(argv[i], "----ftrace") == 0) {
          strcpy(argv[i], "--ftrace");
        }
      }
    } else {
      argv[i - 1] = argv[i];
    }
  }
  if (foundflag) {
    --argc;
    g_buf[0] = '+';
    g_buf[1] = ' ';
    if ((g_symbols = OpenSymbolTable(FindDebugBinary()))) {
      __hook(ftrace_hook, g_symbols);
    }
  }
  return argc;
}