15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Copyright (c) 2009 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This file implements BSD-style setproctitle() for Linux. 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// It is written such that it can easily be compiled outside Chromium. 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// The Linux kernel sets up two locations in memory to pass arguments and 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// environment variables to processes. First, there are two char* arrays stored 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// one after another: argv and environ. A pointer to argv is passed to main(), 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// while glibc sets the global variable |environ| to point at the latter. Both 125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// of these arrays are terminated by a NULL pointer; the environment array is 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// also followed by some empty space to allow additional variables to be added. 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// These arrays contain pointers to a second location in memory, where the 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// strings themselves are stored one after another: first all the arguments, 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// then the environment variables. The kernel will allocate a single page of 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// memory for this purpose, so the end of the page containing argv[0] is the 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// end of the storage potentially available to store the process title. 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// When the kernel reads the command line arguments for a process, it looks at 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// the range of memory within this page that it initially used for the argument 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// list. If the terminating '\0' character is still where it expects, nothing 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// further is done. If it has been overwritten, the kernel will scan up to the 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// size of a page looking for another. (Note, however, that in general not that 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// much space is actually mapped, since argv[0] is rarely page-aligned and only 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// one page is mapped.) 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Thus to change the process title, we must move any environment variables out 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// of the way to make room for a potentially longer title, and then overwrite 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// the memory pointed to by argv[0] with a single replacement string, making 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// sure its size does not exceed the available space. 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// It is perhaps worth noting that patches to add a system call to Linux for 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// this, like in BSD, have never made it in: this is the "official" way to do 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// this on Linux. Presumably it is not in glibc due to some disagreement over 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// this position within the glibc project, leaving applications caught in the 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// middle. (Also, only a very few applications need or want this anyway.) 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "content/common/set_process_title_linux.h" 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include <stdarg.h> 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include <stdint.h> 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include <stdio.h> 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include <string.h> 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include <unistd.h> 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)extern char** environ; 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)static char** g_main_argv = NULL; 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)static char* g_orig_argv0 = NULL; 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)void setproctitle(const char* fmt, ...) { 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) va_list ap; 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) size_t i, avail_size; 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) uintptr_t page_size, page, page_end; 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Sanity check before we try and set the process title. 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // The BSD version allows fmt == NULL to restore the original title. 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (!g_main_argv || !environ || !fmt) 605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return; 615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (!g_orig_argv0) { 625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Save the original argv[0]. 635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) g_orig_argv0 = strdup(g_main_argv[0]); 645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (!g_orig_argv0) 655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return; 665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) page_size = sysconf(_SC_PAGESIZE); 685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Get the page on which the argument list and environment live. 695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) page = (uintptr_t) g_main_argv[0]; 705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) page -= page % page_size; 715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) page_end = page + page_size; 725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Move the environment out of the way. Note that we are moving the values, 735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // not the environment array itself (which may not be on the page we need 745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // to overwrite anyway). 755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) for (i = 0; environ[i]; ++i) { 765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) uintptr_t env_i = (uintptr_t) environ[i]; 775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Only move the value if it's actually in the way. This avoids 785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // leaking copies of the values if this function is called again. 795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (page <= env_i && env_i < page_end) { 805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) char* copy = strdup(environ[i]); 815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Be paranoid. Check for allocation failure and bail out. 825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (!copy) 835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return; 845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) environ[i] = copy; 855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Put the title in argv[0]. We have to zero out the space first since the 885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // kernel doesn't actually look for a null terminator unless we make the 895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // argument list longer than it started. 905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) avail_size = page_end - (uintptr_t) g_main_argv[0]; 915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) memset(g_main_argv[0], 0, avail_size); 925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) va_start(ap, fmt); 935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (fmt[0] == '-') { 945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) vsnprintf(g_main_argv[0], avail_size, &fmt[1], ap); 955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } else { 965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) size_t size = snprintf(g_main_argv[0], avail_size, "%s ", g_orig_argv0); 975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (size < avail_size) 985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) vsnprintf(g_main_argv[0] + size, avail_size - size, fmt, ap); 995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) } 1005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) va_end(ap); 1015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) g_main_argv[1] = NULL; 1025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} 1035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// A version of this built into glibc would not need this function, since 1055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// it could stash the argv pointer in __libc_start_main(). But we need it. 1065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)void setproctitle_init(const char** main_argv) { 1075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (g_main_argv) 1085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) return; 1095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) uintptr_t page_size = sysconf(_SC_PAGESIZE); 1115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Check that the argv array is in fact on the same page of memory 1125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // as the environment array just as an added measure of protection. 1135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) if (((uintptr_t) environ) / page_size == ((uintptr_t) main_argv) / page_size) 1145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) g_main_argv = const_cast<char**>(main_argv); 1155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} 116