327 lines
12 KiB
C
327 lines
12 KiB
C
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#include <defs.h>
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#include <x86.h>
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#include <stab.h>
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#include <stdio.h>
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#include <string.h>
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#include <sync.h>
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#include <kdebug.h>
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#include <kmonitor.h>
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#include <assert.h>
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#define STACKFRAME_DEPTH 20
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extern const struct stab __STAB_BEGIN__[]; // beginning of stabs table
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extern const struct stab __STAB_END__[]; // end of stabs table
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extern const char __STABSTR_BEGIN__[]; // beginning of string table
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extern const char __STABSTR_END__[]; // end of string table
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/* debug information about a particular instruction pointer */
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struct eipdebuginfo {
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const char *eip_file; // source code filename for eip
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int eip_line; // source code line number for eip
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const char *eip_fn_name; // name of function containing eip
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int eip_fn_namelen; // length of function's name
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uintptr_t eip_fn_addr; // start address of function
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int eip_fn_narg; // number of function arguments
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};
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/* *
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* stab_binsearch - according to the input, the initial value of
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* range [*@region_left, *@region_right], find a single stab entry
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* that includes the address @addr and matches the type @type,
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* and then save its boundary to the locations that pointed
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* by @region_left and @region_right.
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*
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* Some stab types are arranged in increasing order by instruction address.
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* For example, N_FUN stabs (stab entries with n_type == N_FUN), which
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* mark functions, and N_SO stabs, which mark source files.
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*
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* Given an instruction address, this function finds the single stab entry
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* of type @type that contains that address.
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*
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* The search takes place within the range [*@region_left, *@region_right].
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* Thus, to search an entire set of N stabs, you might do:
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*
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* left = 0;
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* right = N - 1; (rightmost stab)
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* stab_binsearch(stabs, &left, &right, type, addr);
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*
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* The search modifies *region_left and *region_right to bracket the @addr.
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* *@region_left points to the matching stab that contains @addr,
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* and *@region_right points just before the next stab.
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* If *@region_left > *region_right, then @addr is not contained in any
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* matching stab.
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*
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* For example, given these N_SO stabs:
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* Index Type Address
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* 0 SO f0100000
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* 13 SO f0100040
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* 117 SO f0100176
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* 118 SO f0100178
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* 555 SO f0100652
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* 556 SO f0100654
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* 657 SO f0100849
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* this code:
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* left = 0, right = 657;
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* stab_binsearch(stabs, &left, &right, N_SO, 0xf0100184);
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* will exit setting left = 118, right = 554.
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* */
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static void
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stab_binsearch(const struct stab *stabs, int *region_left, int *region_right,
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int type, uintptr_t addr) {
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int l = *region_left, r = *region_right, any_matches = 0;
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while (l <= r) {
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int true_m = (l + r) / 2, m = true_m;
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// search for earliest stab with right type
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while (m >= l && stabs[m].n_type != type) {
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m --;
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}
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if (m < l) { // no match in [l, m]
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l = true_m + 1;
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continue;
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}
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// actual binary search
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any_matches = 1;
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if (stabs[m].n_value < addr) {
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*region_left = m;
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l = true_m + 1;
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} else if (stabs[m].n_value > addr) {
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*region_right = m - 1;
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r = m - 1;
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} else {
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// exact match for 'addr', but continue loop to find
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// *region_right
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*region_left = m;
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l = m;
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addr ++;
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}
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}
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if (!any_matches) {
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*region_right = *region_left - 1;
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}
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else {
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// find rightmost region containing 'addr'
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l = *region_right;
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for (; l > *region_left && stabs[l].n_type != type; l --)
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/* do nothing */;
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*region_left = l;
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}
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}
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/* *
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* debuginfo_eip - Fill in the @info structure with information about
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* the specified instruction address, @addr. Returns 0 if information
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* was found, and negative if not. But even if it returns negative it
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* has stored some information into '*info'.
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* */
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int
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debuginfo_eip(uintptr_t addr, struct eipdebuginfo *info) {
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const struct stab *stabs, *stab_end;
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const char *stabstr, *stabstr_end;
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info->eip_file = "<unknown>";
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info->eip_line = 0;
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info->eip_fn_name = "<unknown>";
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info->eip_fn_namelen = 9;
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info->eip_fn_addr = addr;
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info->eip_fn_narg = 0;
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stabs = __STAB_BEGIN__;
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stab_end = __STAB_END__;
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stabstr = __STABSTR_BEGIN__;
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stabstr_end = __STABSTR_END__;
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// String table validity checks
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if (stabstr_end <= stabstr || stabstr_end[-1] != 0) {
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return -1;
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}
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// Now we find the right stabs that define the function containing
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// 'eip'. First, we find the basic source file containing 'eip'.
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// Then, we look in that source file for the function. Then we look
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// for the line number.
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// Search the entire set of stabs for the source file (type N_SO).
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int lfile = 0, rfile = (stab_end - stabs) - 1;
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stab_binsearch(stabs, &lfile, &rfile, N_SO, addr);
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if (lfile == 0)
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return -1;
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// Search within that file's stabs for the function definition
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// (N_FUN).
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int lfun = lfile, rfun = rfile;
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int lline, rline;
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stab_binsearch(stabs, &lfun, &rfun, N_FUN, addr);
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if (lfun <= rfun) {
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// stabs[lfun] points to the function name
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// in the string table, but check bounds just in case.
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if (stabs[lfun].n_strx < stabstr_end - stabstr) {
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info->eip_fn_name = stabstr + stabs[lfun].n_strx;
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}
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info->eip_fn_addr = stabs[lfun].n_value;
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addr -= info->eip_fn_addr;
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// Search within the function definition for the line number.
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lline = lfun;
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rline = rfun;
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} else {
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// Couldn't find function stab! Maybe we're in an assembly
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// file. Search the whole file for the line number.
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info->eip_fn_addr = addr;
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lline = lfile;
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rline = rfile;
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}
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info->eip_fn_namelen = strfind(info->eip_fn_name, ':') - info->eip_fn_name;
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// Search within [lline, rline] for the line number stab.
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// If found, set info->eip_line to the right line number.
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// If not found, return -1.
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stab_binsearch(stabs, &lline, &rline, N_SLINE, addr);
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if (lline <= rline) {
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info->eip_line = stabs[rline].n_desc;
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} else {
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return -1;
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}
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// Search backwards from the line number for the relevant filename stab.
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// We can't just use the "lfile" stab because inlined functions
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// can interpolate code from a different file!
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// Such included source files use the N_SOL stab type.
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while (lline >= lfile
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&& stabs[lline].n_type != N_SOL
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&& (stabs[lline].n_type != N_SO || !stabs[lline].n_value)) {
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lline --;
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}
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if (lline >= lfile && stabs[lline].n_strx < stabstr_end - stabstr) {
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info->eip_file = stabstr + stabs[lline].n_strx;
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}
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// Set eip_fn_narg to the number of arguments taken by the function,
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// or 0 if there was no containing function.
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if (lfun < rfun) {
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for (lline = lfun + 1;
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lline < rfun && stabs[lline].n_type == N_PSYM;
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lline ++) {
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info->eip_fn_narg ++;
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}
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}
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return 0;
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}
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/* *
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* print_kerninfo - print the information about kernel, including the location
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* of kernel entry, the start addresses of data and text segements, the start
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* address of free memory and how many memory that kernel has used.
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* */
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void
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print_kerninfo(void) {
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extern char etext[], edata[], end[], kern_init[];
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cprintf("Special kernel symbols:\n");
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cprintf(" entry 0x%08x (phys)\n", kern_init);
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cprintf(" etext 0x%08x (phys)\n", etext);
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cprintf(" edata 0x%08x (phys)\n", edata);
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cprintf(" end 0x%08x (phys)\n", end);
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cprintf("Kernel executable memory footprint: %dKB\n", (end - kern_init + 1023)/1024);
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}
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/* *
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* print_debuginfo - read and print the stat information for the address @eip,
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* and info.eip_fn_addr should be the first address of the related function.
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* */
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void
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print_debuginfo(uintptr_t eip) {
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struct eipdebuginfo info;
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if (debuginfo_eip(eip, &info) != 0) {
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cprintf(" <unknow>: -- 0x%08x --\n", eip);
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}
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else {
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char fnname[256];
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int j;
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for (j = 0; j < info.eip_fn_namelen; j ++) {
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fnname[j] = info.eip_fn_name[j];
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}
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fnname[j] = '\0';
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cprintf(" %s:%d: %s+%d\n", info.eip_file, info.eip_line,
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fnname, eip - info.eip_fn_addr);
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}
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}
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static __noinline uint32_t
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read_eip(void) {
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uint32_t eip;
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asm volatile("movl 4(%%ebp), %0" : "=r" (eip));
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return eip;
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}
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/* *
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* print_stackframe - print a list of the saved eip values from the nested 'call'
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* instructions that led to the current point of execution
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*
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* The x86 stack pointer, namely esp, points to the lowest location on the stack
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* that is currently in use. Everything below that location in stack is free. Pushing
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* a value onto the stack will invole decreasing the stack pointer and then writing
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* the value to the place that stack pointer pointes to. And popping a value do the
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* opposite.
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*
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* The ebp (base pointer) register, in contrast, is associated with the stack
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* primarily by software convention. On entry to a C function, the function's
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* prologue code normally saves the previous function's base pointer by pushing
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* it onto the stack, and then copies the current esp value into ebp for the duration
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* of the function. If all the functions in a program obey this convention,
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* then at any given point during the program's execution, it is possible to trace
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* back through the stack by following the chain of saved ebp pointers and determining
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* exactly what nested sequence of function calls caused this particular point in the
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* program to be reached. This capability can be particularly useful, for example,
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* when a particular function causes an assert failure or panic because bad arguments
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* were passed to it, but you aren't sure who passed the bad arguments. A stack
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* backtrace lets you find the offending function.
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*
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* The inline function read_ebp() can tell us the value of current ebp. And the
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* non-inline function read_eip() is useful, it can read the value of current eip,
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* since while calling this function, read_eip() can read the caller's eip from
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* stack easily.
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*
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* In print_debuginfo(), the function debuginfo_eip() can get enough information about
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* calling-chain. Finally print_stackframe() will trace and print them for debugging.
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*
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* Note that, the length of ebp-chain is limited. In boot/bootasm.S, before jumping
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* to the kernel entry, the value of ebp has been set to zero, that's the boundary.
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* */
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void
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print_stackframe(void) {
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/* LAB1 2012011346 : STEP 1 */
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/* (1) call read_ebp() to get the value of ebp. the type is (uint32_t);
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* (2) call read_eip() to get the value of eip. the type is (uint32_t);
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* (3) from 0 .. STACKFRAME_DEPTH
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* (3.1) printf value of ebp, eip
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* (3.2) (uint32_t)calling arguments [0..4] = the contents in address (unit32_t)ebp +2 [0..4]
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* (3.3) cprintf("\n");
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* (3.4) call print_debuginfo(eip-1) to print the C calling function name and line number, etc.
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* (3.5) popup a calling stackframe
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* NOTICE: the calling funciton's return addr eip = ss:[ebp+4]
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* the calling funciton's ebp = ss:[ebp]
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*/
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uint32_t ebp, eip;
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int i, j;
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ebp = read_ebp();
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eip = read_eip();
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for (i = 0; i < STACKFRAME_DEPTH; i++) {
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uint32_t *start = (uint32_t *)ebp + 2;
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cprintf("ebp:0x%08x eip:0x%08x args:", ebp, eip);
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for (j = 0; j < 4; j++) {
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cprintf("0x%08x", *(start + j));
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if (j != 3)
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cprintf(" ");
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}
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cprintf("\n");
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print_debuginfo(eip - 1);
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ebp = *((uint32_t *)ebp);
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eip = *((uint32_t *)ebp + 1);
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}
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}
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