forked from Imagelibrary/binutils-gdb
c263c0ddcf
When running test-case gdb.ada/convvar_comp.exp on s390x-linux, I get:
...
(gdb) run ^M
Starting program: pb16_063 ^M
^M
Breakpoint 1, pck.break_me (item=...) at pck.adb:17^M
17 function Break_Me (Item : T) return Boolean is^M
(gdb) print item.started^M
Cannot access memory at address 0x0^M
(gdb) FAIL: gdb.ada/convvar_comp.exp: print item.started
...
This happens as follows.
The parameter item is available in (DW_OP_fbreg: -168):
...
<2><912>: Abbrev Number: 18 (DW_TAG_formal_parameter)
<913> DW_AT_name : (indirect string, offset: 0x14ca): item
<919> DW_AT_type : <0x929>
<91d> DW_AT_location : 3 byte block: 91 d8 7e (DW_OP_fbreg: -168)
...
and according to the rules of -O0, it's considered to be available after the
prologue, which looks like this:
...
0000000001002998 <pck__break_me>:
1002998: b3 c1 00 2b ldgr %f2,%r11
100299c: b3 c1 00 0f ldgr %f0,%r15
10029a0: e3 f0 ff 58 ff 71 lay %r15,-168(%r15)
10029a6: b9 04 00 bf lgr %r11,%r15
10029aa: e3 20 b0 a0 00 24 stg %r2,160(%r11)
...
To detect the prologue, gdb checks the line info, which looks like this:
...
pck.adb:
File name Line number Starting address View Stmt
pck.adb 17 0x1002998 x
pck.adb 17 0x1002998 1 x
pck.adb 19 0x10029b0 x
pck.adb 20 0x10029b8 x
pck.adb - 0x10029c6
...
and gdb concludes that it's an empty prologue, so we stop at 0x1002998 and
try to print parameter item, which is not available yet.
For more details, see this comment in skip_prologue_using_sal:
...
/* For languages other than assembly, treat two consecutive line
entries at the same address as a zero-instruction prologue.
...
The same thing happens on x86_64-linux, but it causes no problem there,
because amd64_skip_prologue decides not to trust the result:
...
struct compunit_symtab *cust = find_pc_compunit_symtab (func_addr);
/* LLVM backend (Clang/Flang) always emits a line note before the
prologue and another one after. We trust clang and newer Intel
compilers to emit usable line notes. */
if (post_prologue_pc
&& (cust != NULL
&& cust->producer () != nullptr
&& (producer_is_llvm (cust->producer ())
|| producer_is_icc_ge_19 (cust->producer ()))))
return std::max (start_pc, post_prologue_pc);
...
because the producer is GCC.
Work around this by setting a breakpoint on the first statement of
pck.break_me instead.
Tested on s390x-linux.