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maps: handle the gap behind .text of the exe #124

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Jul 23, 2015
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maps: handle the gap behind .text of the exe #124

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45 changes: 35 additions & 10 deletions maps.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
Copyright (C) 2006,2007,2009 Tavis Ormandy <taviso@sdf.lonestar.org>
Copyright (C) 2009 Eli Dupree <elidupree@charter.net>
Copyright (C) 2009,2010 WANG Lu <coolwanglu@gmail.com>
Copyright (C) 2014,2015 Sebastian Parschauer <s.parschauer@gmx.de>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
Expand Down Expand Up @@ -48,9 +49,9 @@ bool readmaps(pid_t target, list_t * regions)
char name[128], *line = NULL;
char exelink[128];
size_t len = 0;
unsigned int code_regions = 0;
unsigned int code_regions = 0, exe_regions = 0;
unsigned long prev_end = 0, load_addr = 0, exe_load = 0;
bool is_exe = false;
unsigned long prev_end = 0, load_addr = 0;

#define MAX_LINKBUF_SIZE 256
char linkbuf[MAX_LINKBUF_SIZE], *exename = linkbuf;
Expand Down Expand Up @@ -104,46 +105,70 @@ bool readmaps(pid_t target, list_t * regions)
if (sscanf(line, "%lx-%lx %c%c%c%c %x %x:%x %u %s", &start, &end, &read,
&write, &exec, &cow, &offset, &dev_major, &dev_minor, &inode, filename) >= 6) {
/*
* get the load address for regions of the same ELF binary
* get the load address for regions of the same ELF file
*
* When a dynamic loader loads an executable or a library into
* memory, there is one region per binary segment created:
* When the ELF loader loads an executable or a library into
* memory, there is one region per ELF segment created:
* .text (r-x), .rodata (r--), .data (rw-) and .bss (rw-). The
* 'x' permission of .text is used to detect the load address
* (region start) and the end of the binary in memory. All
* (region start) and the end of the ELF file in memory. All
* these regions have the same filename. The only exception
* is the .bss region. Its filename is empty and it is
* consecutive with the .data region. But the regions .bss and
* .rodata may not be present with some binaries. This is why
* .rodata may not be present with some ELF files. This is why
* we can't rely on other regions to be consecutive in memory.
* There should never be more than these four regions.
* The data regions use their variables relative to the load
* address. So determining it makes sense as we can get the
* variable address used within the binariy with it.
* variable address used within the ELF file with it.
* But for the executable there is the special case that there
* is a gap between .text and .rodata. Other regions might be
* loaded via mmap() to it. So we have to count the number of
* regions belonging to the exe separately to handle that.
* References:
* http://en.wikipedia.org/wiki/Executable_and_Linkable_Format
* http://wiki.osdev.org/ELF
* http://lwn.net/Articles/531148/
*/

/* detect further regions of the same ELF file and its end */
if (code_regions > 0) {
if (exec == 'x' || (strncmp(filename, binname,
MAX_LINKBUF_SIZE) != 0 && (filename[0] != '\0' ||
start != prev_end)) || code_regions >= 4) {
code_regions = 0;
is_exe = false;
/* exe with .text and without .data is impossible */
if (exe_regions > 1)
exe_regions = 0;
} else {
code_regions++;
if (is_exe)
exe_regions++;
}
}
if (code_regions == 0) {
/* detect the first region belonging to an ELF file */
if (exec == 'x' && filename[0] != '\0') {
code_regions++;
if (strncmp(filename, exename, MAX_LINKBUF_SIZE) == 0)
if (strncmp(filename, exename, MAX_LINKBUF_SIZE) == 0) {
exe_regions = 1;
exe_load = start;
is_exe = true;
}
strncpy(binname, filename, MAX_LINKBUF_SIZE);
binname[MAX_LINKBUF_SIZE - 1] = '\0'; /* just to be sure */
/* detect the second region of the exe after skipping regions */
} else if (exe_regions == 1 && filename[0] != '\0' &&
strncmp(filename, exename, MAX_LINKBUF_SIZE) == 0) {
code_regions = ++exe_regions;
load_addr = exe_load;
is_exe = true;
strncpy(binname, filename, MAX_LINKBUF_SIZE);
binname[MAX_LINKBUF_SIZE - 1] = '\0'; /* just to be sure */
}
load_addr = start;
if (exe_regions < 2)
load_addr = start;
}
prev_end = end;

Expand Down