Re: [PATCH 4/5] ARM: read_pieced_value do big endian processing only in case of valid gdb_regnum

Yao Qi
2014-10-23T03:22:51Z

Victor Kamensky <victor.kamensky@linaro.org> writes:

> In both little endian and big endian cases compiler generate DW_OP_reg29-
> DW_OP_reg31 something like this.
>
> <2><792>: Abbrev Number: 10 (DW_TAG_formal_parameter)
> <793> DW_AT_name : u
> <795> DW_AT_decl_file : 1
> <796> DW_AT_decl_line : 115
> <797> DW_AT_type : <0x57c>
> <79b> DW_AT_location : 6 byte block: 6d 93 4 6c 93 4
> (DW_OP_reg29 (r29); DW_OP_piece: 4; DW_OP_reg28 (r28); DW_OP_piece: 4)
>

This is quite illustrative.

> I strongly suspect that it is compiler error, but more accurately
> it is hard to say, because I never saw a document where for given CPU
> mapping from registers to DWARF reg numbers is defined. Have you
> seen such document for example for ARM V7? In any case for this
> test case Gdb believes that those register numbers are wrong. I.e we
> can say for sure that gcc and gdb are disagrees.

You need doc "DWARF for the ARM Architecture", which has a table about
the mapping between dwarf reg numbers and processor registers. For the
table, we can see that dwarf register 16 to 63 doesn't map to any
processor registers.

>
>
> (gdb) file /wd1/gdb/20140930/build-v7le/gdb/testsuite/gdb.base/store
> Reading symbols from /wd1/gdb/20140930/build-v7le/gdb/testsuite/gdb.base/store...done.
> (gdb) tbreak wack_double
> Temporary breakpoint 1 at 0x1076c: file ../../../binutils-gdb/gdb/testsuite/gdb.base/store.c, line 117.
> (gdb) run
> Starting program: /wd1/gdb/20140930/build-v7le/gdb/testsuite/gdb.base/store
>
> Temporary breakpoint 1, wack_double (u=
> ../../binutils-gdb/gdb/regcache.c:177: internal-error: register_size: Assertion `regnum >= 0 && regnum < (gdbarch_num_regs (gdbarch) + gdbarch_num_pseudo_regs (gdbarch))' failed.
> A problem internal to GDB has been detected,
> further debugging may prove unreliable.
>

This is quite useful too.

>
> BE Dump
> =======
>
>
> <1><779>: Abbrev Number: 12 (DW_TAG_subprogram)
> <77a> DW_AT_external : 1
> <77a> DW_AT_name : (indirect string, offset: 0x3c9): wack_double
> <77e> DW_AT_decl_file : 1
> <77f> DW_AT_decl_line : 115
> <780> DW_AT_prototyped : 1
> <780> DW_AT_type : <0x57c>
> <784> DW_AT_low_pc : 0x10758
> <788> DW_AT_high_pc : 0x40
> <78c> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
> <78e> DW_AT_GNU_all_tail_call_sites: 1
> <78e> DW_AT_sibling : <0x7d7>
> <2><792>: Abbrev Number: 10 (DW_TAG_formal_parameter)
> <793> DW_AT_name : u
> <795> DW_AT_decl_file : 1
> <796> DW_AT_decl_line : 115
> <797> DW_AT_type : <0x57c>
> <79b> DW_AT_location : 6 byte block: 6d 93 4 6c 93 4 (DW_OP_reg29 (r29); DW_OP_piece: 4; DW_OP_reg28 (r28); DW_OP_piece: 4)
> <2><7a2>: Abbrev Number: 10 (DW_TAG_formal_parameter)
> <7a3> DW_AT_name : v
> <7a5> DW_AT_decl_file : 1
> <7a6> DW_AT_decl_line : 115
> <7a7> DW_AT_type : <0x57c>
> <7ab> DW_AT_location : 6 byte block: 6f 93 4 6e 93 4 (DW_OP_reg31 (r31); DW_OP_piece: 4; DW_OP_reg30 (r30); DW_OP_piece: 4)
> <2><7b2>: Abbrev Number: 13 (DW_TAG_variable)
> <7b3> DW_AT_name : l
> <7b5> DW_AT_decl_file : 1
> <7b6> DW_AT_decl_line : 117
> <7b7> DW_AT_type : <0x57c>
> <7bb> DW_AT_location : 8 byte block: 90 21 93 4 90 20 93 4 (DW_OP_regx: 33 (r33); DW_OP_piece: 4; DW_OP_regx: 32 (r32); DW_OP_piece: 4)
> <2><7c4>: Abbrev Number: 13 (DW_TAG_variable)
> <7c5> DW_AT_name : r
> <7c7> DW_AT_decl_file : 1
> <7c8> DW_AT_decl_line : 117
> <7c9> DW_AT_type : <0x57c>
> <7cd> DW_AT_location : 8 byte block: 90 23 93 4 90 22 93 4 (DW_OP_regx: 35 (r35); DW_OP_piece: 4; DW_OP_regx: 34 (r34); DW_OP_piece: 4)
>

However, we don't need to copy the whole DIE here, instead, we can only
copy one DW_TAG_formal_parameter, which is should be illustrative enough
for the problem.

> Backtrace when it failed to get reg number
> ==========================================

We don't need to copy the full stack back trace here.

--
Yao (齐尧)