/* Target-dependent code for GDB, the GNU debugger.
- Copyright 1986, 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 2000
- Free Software Foundation, Inc.
+
+ Copyright 1986, 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997,
+ 2000, 2001 Free Software Foundation, Inc.
This file is part of GDB.
#include "gdbcmd.h"
#include "symfile.h"
#include "objfiles.h"
+#include "regcache.h"
+#include "value.h"
+
+#include "solib-svr4.h"
+#include "ppc-tdep.h"
/* The following two instructions are used in the signal trampoline
code on linux/ppc */
#define PPC_LINUX_PT_FPR31 (PPC_LINUX_PT_FPR0 + 2*31)
#define PPC_LINUX_PT_FPSCR (PPC_LINUX_PT_FPR0 + 2*32 + 1)
+static int ppc_linux_at_sigtramp_return_path (CORE_ADDR pc);
+
/* Determine if pc is in a signal trampoline...
Ha! That's not what this does at all. wait_for_inferior in infrun.c
char buf[4];
CORE_ADDR handler;
- lr = read_register (LR_REGNUM);
+ lr = read_register (gdbarch_tdep (current_gdbarch)->ppc_lr_regnum);
if (!ppc_linux_at_sigtramp_return_path (lr))
return 0;
* instructions. It'd be faster though if we could find a way to do this
* via some simple address comparisons.
*/
-int
+static int
ppc_linux_at_sigtramp_return_path (CORE_ADDR pc)
{
char buf[12];
/* The rs6000 version of FRAME_SAVED_PC will almost work for us. The
signal handler details are different, so we'll handle those here
and call the rs6000 version to do the rest. */
-unsigned long
+CORE_ADDR
ppc_linux_frame_saved_pc (struct frame_info *fi)
{
if (fi->signal_handler_caller)
{
CORE_ADDR regs_addr =
- read_memory_integer (fi->frame + PPC_LINUX_REGS_PTR_OFFSET, 4);
+ read_memory_integer (fi->frame + PPC_LINUX_REGS_PTR_OFFSET, 4);
/* return the NIP in the regs array */
return read_memory_integer (regs_addr + 4 * PPC_LINUX_PT_NIP, 4);
}
-
- return rs6000_frame_saved_pc (fi);
+ else if (fi->next && fi->next->signal_handler_caller)
+ {
+ CORE_ADDR regs_addr =
+ read_memory_integer (fi->next->frame + PPC_LINUX_REGS_PTR_OFFSET, 4);
+ /* return LNK in the regs array */
+ return read_memory_integer (regs_addr + 4 * PPC_LINUX_PT_LNK, 4);
+ }
+ else
+ return rs6000_frame_saved_pc (fi);
}
void
regs_addr =
read_memory_integer (fi->frame + PPC_LINUX_REGS_PTR_OFFSET, 4);
fi->saved_regs[PC_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_NIP;
- fi->saved_regs[PS_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_MSR;
- fi->saved_regs[CR_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_CCR;
- fi->saved_regs[LR_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_LNK;
- fi->saved_regs[CTR_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_CTR;
- fi->saved_regs[XER_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_XER;
- fi->saved_regs[MQ_REGNUM] = regs_addr + 4 * PPC_LINUX_PT_MQ;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_ps_regnum] =
+ regs_addr + 4 * PPC_LINUX_PT_MSR;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_cr_regnum] =
+ regs_addr + 4 * PPC_LINUX_PT_CCR;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_lr_regnum] =
+ regs_addr + 4 * PPC_LINUX_PT_LNK;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_ctr_regnum] =
+ regs_addr + 4 * PPC_LINUX_PT_CTR;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_xer_regnum] =
+ regs_addr + 4 * PPC_LINUX_PT_XER;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_mq_regnum] =
+ regs_addr + 4 * PPC_LINUX_PT_MQ;
for (i = 0; i < 32; i++)
- fi->saved_regs[GP0_REGNUM + i] = regs_addr + 4 * PPC_LINUX_PT_R0 + 4 * i;
+ fi->saved_regs[gdbarch_tdep (current_gdbarch)->ppc_gp0_regnum + i] =
+ regs_addr + 4 * PPC_LINUX_PT_R0 + 4 * i;
for (i = 0; i < 32; i++)
fi->saved_regs[FP0_REGNUM + i] = regs_addr + 4 * PPC_LINUX_PT_FPR0 + 8 * i;
}
starting from r4. */
CORE_ADDR
-ppc_sysv_abi_push_arguments (nargs, args, sp, struct_return, struct_addr)
- int nargs;
- value_ptr *args;
- CORE_ADDR sp;
- int struct_return;
- CORE_ADDR struct_addr;
+ppc_sysv_abi_push_arguments (int nargs, struct value **args, CORE_ADDR sp,
+ int struct_return, CORE_ADDR struct_addr)
{
int argno;
int greg, freg;
int structstkspace;
int argoffset;
int structoffset;
- value_ptr arg;
+ struct value *arg;
struct type *type;
int len;
char old_sp_buf[4];
structoffset = argoffset + argstkspace;
freg = 1;
greg = 3;
+ /* Fill in r3 with the return structure, if any */
+ if (struct_return)
+ {
+ char val_buf[4];
+ store_address (val_buf, 4, struct_addr);
+ memcpy (®isters[REGISTER_BYTE (greg)], val_buf, 4);
+ greg++;
+ }
/* Now fill in the registers and stack... */
for (argno = 0; argno < nargs; argno++)
{
target_store_registers (-1);
return sp;
}
+
+/* ppc_linux_memory_remove_breakpoints attempts to remove a breakpoint
+ in much the same fashion as memory_remove_breakpoint in mem-break.c,
+ but is careful not to write back the previous contents if the code
+ in question has changed in between inserting the breakpoint and
+ removing it.
+
+ Here is the problem that we're trying to solve...
+
+ Once upon a time, before introducing this function to remove
+ breakpoints from the inferior, setting a breakpoint on a shared
+ library function prior to running the program would not work
+ properly. In order to understand the problem, it is first
+ necessary to understand a little bit about dynamic linking on
+ this platform.
+
+ A call to a shared library function is accomplished via a bl
+ (branch-and-link) instruction whose branch target is an entry
+ in the procedure linkage table (PLT). The PLT in the object
+ file is uninitialized. To gdb, prior to running the program, the
+ entries in the PLT are all zeros.
+
+ Once the program starts running, the shared libraries are loaded
+ and the procedure linkage table is initialized, but the entries in
+ the table are not (necessarily) resolved. Once a function is
+ actually called, the code in the PLT is hit and the function is
+ resolved. In order to better illustrate this, an example is in
+ order; the following example is from the gdb testsuite.
+
+ We start the program shmain.
+
+ [kev@arroyo testsuite]$ ../gdb gdb.base/shmain
+ [...]
+
+ We place two breakpoints, one on shr1 and the other on main.
+
+ (gdb) b shr1
+ Breakpoint 1 at 0x100409d4
+ (gdb) b main
+ Breakpoint 2 at 0x100006a0: file gdb.base/shmain.c, line 44.
+
+ Examine the instruction (and the immediatly following instruction)
+ upon which the breakpoint was placed. Note that the PLT entry
+ for shr1 contains zeros.
+
+ (gdb) x/2i 0x100409d4
+ 0x100409d4 <shr1>: .long 0x0
+ 0x100409d8 <shr1+4>: .long 0x0
+
+ Now run 'til main.
+
+ (gdb) r
+ Starting program: gdb.base/shmain
+ Breakpoint 1 at 0xffaf790: file gdb.base/shr1.c, line 19.
+
+ Breakpoint 2, main ()
+ at gdb.base/shmain.c:44
+ 44 g = 1;
+
+ Examine the PLT again. Note that the loading of the shared
+ library has initialized the PLT to code which loads a constant
+ (which I think is an index into the GOT) into r11 and then
+ branchs a short distance to the code which actually does the
+ resolving.
+
+ (gdb) x/2i 0x100409d4
+ 0x100409d4 <shr1>: li r11,4
+ 0x100409d8 <shr1+4>: b 0x10040984 <sg+4>
+ (gdb) c
+ Continuing.
+
+ Breakpoint 1, shr1 (x=1)
+ at gdb.base/shr1.c:19
+ 19 l = 1;
+
+ Now we've hit the breakpoint at shr1. (The breakpoint was
+ reset from the PLT entry to the actual shr1 function after the
+ shared library was loaded.) Note that the PLT entry has been
+ resolved to contain a branch that takes us directly to shr1.
+ (The real one, not the PLT entry.)
+
+ (gdb) x/2i 0x100409d4
+ 0x100409d4 <shr1>: b 0xffaf76c <shr1>
+ 0x100409d8 <shr1+4>: b 0x10040984 <sg+4>
+
+ The thing to note here is that the PLT entry for shr1 has been
+ changed twice.
+
+ Now the problem should be obvious. GDB places a breakpoint (a
+ trap instruction) on the zero value of the PLT entry for shr1.
+ Later on, after the shared library had been loaded and the PLT
+ initialized, GDB gets a signal indicating this fact and attempts
+ (as it always does when it stops) to remove all the breakpoints.
+
+ The breakpoint removal was causing the former contents (a zero
+ word) to be written back to the now initialized PLT entry thus
+ destroying a portion of the initialization that had occurred only a
+ short time ago. When execution continued, the zero word would be
+ executed as an instruction an an illegal instruction trap was
+ generated instead. (0 is not a legal instruction.)
+
+ The fix for this problem was fairly straightforward. The function
+ memory_remove_breakpoint from mem-break.c was copied to this file,
+ modified slightly, and renamed to ppc_linux_memory_remove_breakpoint.
+ In tm-linux.h, MEMORY_REMOVE_BREAKPOINT is defined to call this new
+ function.
+
+ The differences between ppc_linux_memory_remove_breakpoint () and
+ memory_remove_breakpoint () are minor. All that the former does
+ that the latter does not is check to make sure that the breakpoint
+ location actually contains a breakpoint (trap instruction) prior
+ to attempting to write back the old contents. If it does contain
+ a trap instruction, we allow the old contents to be written back.
+ Otherwise, we silently do nothing.
+
+ The big question is whether memory_remove_breakpoint () should be
+ changed to have the same functionality. The downside is that more
+ traffic is generated for remote targets since we'll have an extra
+ fetch of a memory word each time a breakpoint is removed.
+
+ For the time being, we'll leave this self-modifying-code-friendly
+ version in ppc-linux-tdep.c, but it ought to be migrated somewhere
+ else in the event that some other platform has similar needs with
+ regard to removing breakpoints in some potentially self modifying
+ code. */
+int
+ppc_linux_memory_remove_breakpoint (CORE_ADDR addr, char *contents_cache)
+{
+ unsigned char *bp;
+ int val;
+ int bplen;
+ char old_contents[BREAKPOINT_MAX];
+
+ /* Determine appropriate breakpoint contents and size for this address. */
+ bp = BREAKPOINT_FROM_PC (&addr, &bplen);
+ if (bp == NULL)
+ error ("Software breakpoints not implemented for this target.");
+
+ val = target_read_memory (addr, old_contents, bplen);
+
+ /* If our breakpoint is no longer at the address, this means that the
+ program modified the code on us, so it is wrong to put back the
+ old value */
+ if (val == 0 && memcmp (bp, old_contents, bplen) == 0)
+ val = target_write_memory (addr, contents_cache, bplen);
+
+ return val;
+}
+
+/* Fetch (and possibly build) an appropriate link_map_offsets
+ structure for Linux/PPC targets using the struct offsets
+ defined in link.h (but without actual reference to that file).
+
+ This makes it possible to access Linux/PPC shared libraries from a
+ GDB that was not built on an Linux/PPC host (for cross debugging). */
+
+struct link_map_offsets *
+ppc_linux_svr4_fetch_link_map_offsets (void)
+{
+ static struct link_map_offsets lmo;
+ static struct link_map_offsets *lmp = NULL;
+
+ if (lmp == NULL)
+ {
+ lmp = &lmo;
+
+ lmo.r_debug_size = 8; /* The actual size is 20 bytes, but
+ this is all we need. */
+ lmo.r_map_offset = 4;
+ lmo.r_map_size = 4;
+
+ lmo.link_map_size = 20; /* The actual size is 560 bytes, but
+ this is all we need. */
+ lmo.l_addr_offset = 0;
+ lmo.l_addr_size = 4;
+
+ lmo.l_name_offset = 4;
+ lmo.l_name_size = 4;
+
+ lmo.l_next_offset = 12;
+ lmo.l_next_size = 4;
+
+ lmo.l_prev_offset = 16;
+ lmo.l_prev_size = 4;
+ }
+
+ return lmp;
+}
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