Run Time linker and relocation of multiple local labels
dufault at hda.com
dufault at hda.com
Thu Apr 25 16:04:51 UTC 2019
In a given object file for "NOTYPE LOCAL” entries in a data segment with zero size that don’t start with ‘$’ could you append text based on the Num field for the rtems_rtl_obj symbol lookup in cpukit/libdl/rtl-sym.c? Right now it’s a linear lookup on e.g. “.LC2” and stops at the first hit. I haven’t checked that consumers of the lookup can generate the correct name, that is, always have the “Num” field value.
You’d wind up with mangled lookups such as:
22: 0000002c 0 NOTYPE LOCAL DEFAULT 3 .LC2.Num22
44: 0000013c 0 NOTYPE LOCAL DEFAULT 3 .LC2.Num44
This is from one of my relocatable files grepping for NOTYPE LOCAL. I’ve verified large files also work.
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
14: 00000000 0 NOTYPE LOCAL DEFAULT 3 $d
15: 00000000 0 NOTYPE LOCAL DEFAULT 4 $d
17: 00000000 0 NOTYPE LOCAL DEFAULT 6 $d
18: 00000000 2048 NOTYPE LOCAL DEFAULT 6 env_entries
20: 00000800 4 NOTYPE LOCAL DEFAULT 6 env_initialized
21: 00000008 0 NOTYPE LOCAL DEFAULT 3 .LC1
22: 0000002c 0 NOTYPE LOCAL DEFAULT 3 .LC2
23: 00000030 0 NOTYPE LOCAL DEFAULT 3 .LC3
25: 00000000 0 NOTYPE LOCAL DEFAULT 1 $t
28: 00000050 0 NOTYPE LOCAL DEFAULT 3 .LC4
29: 00000058 0 NOTYPE LOCAL DEFAULT 3 .LC5
30: 00000080 0 NOTYPE LOCAL DEFAULT 3 .LC6
32: 00000094 0 NOTYPE LOCAL DEFAULT 3 .LC7
33: 000000c4 0 NOTYPE LOCAL DEFAULT 3 .LC8
34: 000000cc 0 NOTYPE LOCAL DEFAULT 3 .LC9
35: 000000f4 0 NOTYPE LOCAL DEFAULT 3 .LC10
37: 00000130 0 NOTYPE LOCAL DEFAULT 3 $d
38: 0000000c 0 NOTYPE LOCAL DEFAULT 4 $d
40: 00000804 0 NOTYPE LOCAL DEFAULT 6 $d
41: 00000d14 520 NOTYPE LOCAL DEFAULT 6 putenv_trace_ptrs
42: 00000690 0 NOTYPE LOCAL DEFAULT 1 $t
43: 00000138 0 NOTYPE LOCAL DEFAULT 3 .LC1
44: 0000013c 0 NOTYPE LOCAL DEFAULT 3 .LC2
45: 0000014c 0 NOTYPE LOCAL DEFAULT 3 .LC3
47: 00000164 0 NOTYPE LOCAL DEFAULT 3 .LC4
> On Apr 25, 2019, at 07:56 , Peter Dufault <dufault at hda.com> wrote:
>
> I’m porting a large vxWorks application and I’m trying to download “ld -r” files as you can on vxWorks using the run-time loader. At least on ARM I can’t get it to work, it uses the first local address it sees for all occurrences.
>
> Example: Label .LC2 is used in two places, once for the “r” in an fopen() and later for a format string. In both cases the address used is 0x419f14, the address of “r”.
>
> First is the readelf output, then the disassembly, then debugging output from the RTL.
>
> FIRST OCCURRENCE OF .LC2 used as “r” in fopen()
> readelf:
> 00000020 0000152f R_ARM_THM_MOVW_ABS_NC 00000008 .LC1
> 00000024 00001530 R_ARM_THM_MOVT_ABS 00000008 .LC1
> 0000002a 0000162f R_ARM_THM_MOVW_ABS_NC 0000002c .LC2
> 0000002e 00001630 R_ARM_THM_MOVT_ABS 0000002c .LC2
> 00000034 0000450a R_ARM_THM_CALL 00000000 fopen
>
> Disassemble:
> if ((fd = fopen(string, "r")) == (0)) {
> 2a: f240 0100 movw r1, #0
> 2e: f2c0 0100 movt r1, #0
> 32: 6878 ldr r0, [r7, #4]
> 34: f7ff fffe bl 0 <fopen>
>
> RTL:
> rtl: THM_MOVT_ABS/THM_MOVW_ABS_NC 0x341f2c0 @ 0x4196dc in bad
> rtl: rel: sym:.LC2(22)=00419f14 type:47 off:0000002a
> rtl: THM_MOVT_ABS/THM_MOVW_ABS_NC 0x7114f649 @ 0x4196e2 in bad
> rtl: rel: sym:.LC2(22)=00419f14 type:48 off:0000002e
> rtl: THM_MOVT_ABS/THM_MOVW_ABS_NC 0x141f2c0 @ 0x4196e6 in bad
> rtl: rel: sym:fopen(69)=000d33c1 type:10 off:00000034
>
> SECOND OCCURRENCE of .LC2 used for the printf format string:
>
> readelf:
> 000007a8 00002c2f R_ARM_THM_MOVW_ABS_NC 0000013c .LC2
> 000007ac 00002c30 R_ARM_THM_MOVT_ABS 0000013c .LC2
> 000007b0 0000330a R_ARM_THM_CALL 00000000 printf
>
> Disassemble:
> 7a6: 68f9 ldr r1, [r7, #12]
> 7a8: f240 0000 movw r0, #0
> 7ac: f2c0 0000 movt r0, #0
> 7b0: f7ff fffe bl 0 <printf>
>
> RTL:
> rtl: rel: sym:.LC2(44)=00419f14 type:47 off:000007a8
> rtl: THM_MOVT_ABS/THM_MOVW_ABS_NC 0x7014f649 @ 0x419e60 in /opt/flatland/arch/arm-stubs-vxstubs/bin/sys-bad
> rtl: rel: sym:.LC2(44)=00419f14 type:48 off:000007ac
> rtl: THM_MOVT_ABS/THM_MOVW_ABS_NC 0x41f2c0 @ 0x419e64 in /opt/flatland/arch/arm-stubs-vxstubs/bin/sys-bad
> rtl: rel: sym:printf(51)=000daac9 type:10 off:000007b0
>
> Peter
> -----------------
> Peter Dufault
> HD Associates, Inc. Software and System Engineering
>
> This email is delivered through the public internet using protocols subject to interception and tampering.
>
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Peter
-----------------
Peter Dufault
HD Associates, Inc. Software and System Engineering
This email is delivered through the public internet using protocols subject to interception and tampering.
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