From c0c14c1e8d0287456bc4a0c3a2cfc0858589c3d0 Mon Sep 17 00:00:00 2001 From: Jim Kingdon Date: Sun, 17 Oct 1993 14:30:20 +0000 Subject: [PATCH] * infrun.c (wait_for_inferior): Clean up comments which were at the top of the file, making them more concise and moving them with the code (Sorry, Randy, but these stream-of-consciousness comments really have to go). Switch the order of the "&&", which makes things clearer and turns out to be an improvement with respect to side effects and speed. --- gdb/infrun.c | 133 ++++++++++++++++----------------------------------- 1 file changed, 41 insertions(+), 92 deletions(-) diff --git a/gdb/infrun.c b/gdb/infrun.c index bc3e3fc3a6..da5862299e 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -18,90 +18,6 @@ You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ -/* Notes on the algorithm used in wait_for_inferior to determine if we - just did a subroutine call when stepping. We have the following - information at that point: - - Current and previous (just before this step) pc. - Current and previous sp. - Current and previous start of current function. - - If the starts of the functions don't match, then - - a) We did a subroutine call. - - In this case, the pc will be at the beginning of a function. - - b) We did a subroutine return. - - Otherwise. - - c) We did a longjmp. - - If we did a longjump, we were doing "nexti", since a next would - have attempted to skip over the assembly language routine in which - the longjmp is coded and would have simply been the equivalent of a - continue. I consider this ok behaivior. We'd like one of two - things to happen if we are doing a nexti through the longjmp() - routine: 1) It behaves as a stepi, or 2) It acts like a continue as - above. Given that this is a special case, and that anybody who - thinks that the concept of sub calls is meaningful in the context - of a longjmp, I'll take either one. Let's see what happens. - - Acts like a subroutine return. I can handle that with no problem - at all. - - -->So: If the current and previous beginnings of the current - function don't match, *and* the pc is at the start of a function, - we've done a subroutine call. If the pc is not at the start of a - function, we *didn't* do a subroutine call. - - -->If the beginnings of the current and previous function do match, - either: - - a) We just did a recursive call. - - In this case, we would be at the very beginning of a - function and 1) it will have a prologue (don't jump to - before prologue, or 2) (we assume here that it doesn't have - a prologue) there will have been a change in the stack - pointer over the last instruction. (Ie. it's got to put - the saved pc somewhere. The stack is the usual place. In - a recursive call a register is only an option if there's a - prologue to do something with it. This is even true on - register window machines; the prologue sets up the new - window. It might not be true on a register window machine - where the call instruction moved the register window - itself. Hmmm. One would hope that the stack pointer would - also change. If it doesn't, somebody send me a note, and - I'll work out a more general theory. - bug-gdb@prep.ai.mit.edu). This is true (albeit slipperly - so) on all machines I'm aware of: - - m68k: Call changes stack pointer. Regular jumps don't. - - sparc: Recursive calls must have frames and therefor, - prologues. - - vax: All calls have frames and hence change the - stack pointer. - - b) We did a return from a recursive call. I don't see that we - have either the ability or the need to distinguish this - from an ordinary jump. The stack frame will be printed - when and if the frame pointer changes; if we are in a - function without a frame pointer, it's the users own - lookout. - - c) We did a jump within a function. We assume that this is - true if we didn't do a recursive call. - - d) We are in no-man's land ("I see no symbols here"). We - don't worry about this; it will make calls look like simple - jumps (and the stack frames will be printed when the frame - pointer moves), which is a reasonably non-violent response. -*/ - #include "defs.h" #include #include @@ -1051,15 +967,48 @@ same_pid: SKIP_PROLOGUE (prologue_pc); } - /* ==> See comments at top of file on this algorithm. <==*/ + if ((/* Might be a non-recursive call. If the symbols are missing + enough that stop_func_start == prev_func_start even though + they are really two functions, we will treat some calls as + jumps. */ + stop_func_start != prev_func_start - if ((stop_pc < stop_func_start - || stop_pc >= stop_func_end - || stop_pc == stop_func_start - || IN_SOLIB_TRAMPOLINE (stop_pc, stop_func_name)) - && (stop_func_start != prev_func_start - || prologue_pc != stop_func_start - || stop_sp != prev_sp)) + /* Might be a recursive call if either we have a prologue + or the call instruction itself saves the PC on the stack. */ + || prologue_pc != stop_func_start + || stop_sp != prev_sp) + && (/* I think this can only happen if stop_func_start is zero + (e.g. stop_pc is in some objfile we don't know about). + If the stop_pc does that (ends up someplace unknown), it + must be some sort of subroutine call. */ + stop_pc < stop_func_start + || stop_pc >= stop_func_end + + /* If we do a call, we will be at the start of a function. */ + || stop_pc == stop_func_start + +#if 0 + /* Not conservative enough for 4.11. FIXME: enable this + after 4.11. */ + /* Except on the Alpha with -O (and perhaps other machines + with similar calling conventions), in which we might + call the address after the load of gp. Since prologues + don't contain calls, we can't return to within one, and + we don't jump back into them, so this check is OK. */ + || stop_pc < prologue_pc +#endif + + /* If we end up in certain places, it means we did a subroutine + call. I'm not completely sure this is necessary now that we + have the above checks with stop_func_start (and now that + find_pc_partial_function is pickier. */ + || IN_SOLIB_TRAMPOLINE (stop_pc, stop_func_name) + + /* If none of the above apply, it is a jump within a function, + or a return from a subroutine. The other case is longjmp, + which can no longer happen here as long as the + handling_longjmp stuff is working. */ + )) { /* It's a subroutine call. */