+ /* In order to make an interspace call, we need to go through a stub.
+ gcc supplies an appropriate stub called "__gcc_plt_call", however, if
+ an application is compiled with HP compilers then this stub is not
+ available. We used to fallback to "__d_plt_call", however that stub
+ is not entirely useful for us because it doesn't do an interspace
+ return back to the caller. Also, on hppa64-hpux, there is no
+ __gcc_plt_call available. In order to keep the code uniform, we
+ instead don't use either of these stubs, but instead write our own
+ onto the stack.
+
+ A problem arises since the stack is located in a different space than
+ code, so in order to branch to a stack stub, we will need to do an
+ interspace branch. Previous versions of gdb did this by modifying code
+ at the current pc and doing single-stepping to set the pcsq. Since this
+ is highly undesirable, we use a different scheme:
+
+ All we really need to do the branch to the stub is a short instruction
+ sequence like this:
+
+ PA1.1:
+ ldsid (rX),r1
+ mtsp r1,sr0
+ be,n (sr0,rX)
+
+ PA2.0:
+ bve,n (sr0,rX)
+
+ Instead of writing these sequences ourselves, we can find it in
+ the instruction stream that belongs to the current space. While this
+ seems difficult at first, we are actually guaranteed to find the sequences
+ in several places:
+
+ For 32-bit code:
+ - in export stubs for shared libraries
+ - in the "noshlibs" routine in the main module
+
+ For 64-bit code:
+ - at the end of each "regular" function
+
+ We cache the address of these sequences in the objfile's private data
+ since these operations can potentially be quite expensive.
+
+ So, what we do is:
+ - write a stack trampoline
+ - look for a suitable instruction sequence in the current space
+ - point the sequence at the trampoline
+ - set the return address of the trampoline to the current space
+ (see hppa_hpux_find_dummy_call_bpaddr)
+ - set the continuing address of the "dummy code" as the sequence.
+
+*/
+
+ if (IS_32BIT_TARGET (gdbarch))
+ {
+ static unsigned int hppa32_tramp[] = {
+ 0x0fdf1291, /* stw r31,-8(,sp) */
+ 0x02c010a1, /* ldsid (,r22),r1 */
+ 0x00011820, /* mtsp r1,sr0 */
+ 0xe6c00000, /* be,l 0(sr0,r22),%sr0,%r31 */
+ 0x081f0242, /* copy r31,rp */
+ 0x0fd11082, /* ldw -8(,sp),rp */
+ 0x004010a1, /* ldsid (,rp),r1 */
+ 0x00011820, /* mtsp r1,sr0 */
+ 0xe0400000, /* be 0(sr0,rp) */
+ 0x08000240 /* nop */
+ };
+
+ /* for hppa32, we must call the function through a stub so that on
+ return it can return to the space of our trampoline. */
+ stubaddr = hppa_hpux_find_import_stub_for_addr (funcaddr);
+ if (stubaddr == 0)
+ error (_("Cannot call external function not referenced by application "
+ "(no import stub).\n"));
+ regcache_cooked_write_unsigned (regcache, 22, stubaddr);
+
+ write_memory (sp, (char *)&hppa32_tramp, sizeof (hppa32_tramp));
+
+ *bp_addr = hppa_hpux_find_dummy_bpaddr (pc);
+ regcache_cooked_write_unsigned (regcache, 31, *bp_addr);
+
+ *real_pc = hppa32_hpux_search_dummy_call_sequence (gdbarch, pc, &argreg);
+ if (*real_pc == 0)
+ error (_("Cannot make interspace call from here."));
+
+ regcache_cooked_write_unsigned (regcache, argreg, sp);
+
+ sp += sizeof (hppa32_tramp);
+ }
+ else
+ {
+ static unsigned int hppa64_tramp[] = {
+ 0xeac0f000, /* bve,l (r22),%r2 */
+ 0x0fdf12d1, /* std r31,-8(,sp) */
+ 0x0fd110c2, /* ldd -8(,sp),rp */
+ 0xe840d002, /* bve,n (rp) */
+ 0x08000240 /* nop */
+ };