The symptom/problem:
When the target firmware is compiled for big-endian, and when
JLinkGDBServer is running such that the target is big-endian, then
when debugging with gdb the capability to break and step fails.
The question(s) are:
If the remote target is big-endian, and the host is little-endian, is
there something _more_ needed to be done in gdb(1) configuration to
conduct a debug session whereas the endianness of the data and
registers is interpreted as expected?
Is there a setting in gdb that enforces a behavior to step INTO
assembly functions rather than OVER them even when "si" is used?
Setup:
Target device TMS570LC4357 (Hercules, TMS 570) ARM Cortex-R5
Target firmware, C/ASM code compiled as "big endian" (-mbig-endian,
-EB, etc..)
All compilations made with:
$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (15:4.9.3+svn231177-1) 4.9.3 20150529 (prerelease)
$ arm-none-eabi-as --version
GNU assembler (2.26-4ubuntu1+8) 2.26
$ arm-none-eabi-ar --version
GNU ar (2.26-4ubuntu1+8) 2.26
$ arm-none-eabi-ld --version
GNU ld (2.26-4ubuntu1+8) 2.26
Host:
Little-endian Xeon with Ubuntu
Host runs JLinkGDBServer.exe ( version V642-f)
Host runs gdb(1) version 8.2
GDB was configured as follows:
configure --host=x86_64-linux-gnu --target=arm-none-eabi
--with-auto-load-dir=:/auto-load
--with-auto-load-safe-path=:/auto-load
--with-expat
--with-gdb-datadir=/usr/lib/arm-none-eabi/share/gdb
--with-jit-reader-dir=/usr/lib/lib/gdb
--without-libunwind-ia64
--without-lzma
--without-babeltrace
--without-intel-pt
--disable-libmcheck
--without-mpfr
--without-guile
--with-separate-debug-dir=/usr/lib/lib/debug
--with-system-gdbinit=/usr/lib/arm-none-eabi/lib/gdbinit
Data and explanation:
Suppose the firmware has a function at physical address 0x0000003C
(somewhere in the first block of flash)
Suppose the breakpoint set in gdb is at this address.
If the breakpoint is set, and then the firmware is run, the gdb traps
on the breakpoint:
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This GDB was configured as "--host=x86_64-linux-gnu
--target=arm-none-eabi".
Type "show configuration" for configuration details.
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Reading symbols from image.elf...done.
Remote debugging using localhost:2331
0x00000000 in ?? ()
The target endianness is set automatically (currently big endian)
(gdb) load
Loading section .text, size 0x4758 lma 0x20
Loading section .rodata, size 0x200 lma 0x4778
Start address 0x3c, load size 18776
Transfer rate: 6111 KB/sec, 6258 bytes/write.
(gdb) br _c_int00
Breakpoint 1 at 0x3c: file source/HL_sys_startup.c, line 88.
(gdb) c
Continuing.
Program received signal SIGTRAP, Trace/breakpoint trap.
0x3c000000 in ?? ()
(gdb) list
1
2
3 int main()
4 {
5 return 0;
6 }
(gdb) step
Cannot find bounds of current function
Attempts to step fail
"Cannot find bounds of current function"
I presume this is because the big-endian interpretation of the PC is
an address where the function is not located.. The function is at
physical address 0x3C.
(gdb) monitor regs
PC = 3C000000, CPSR = 000003D3 (SVC mode, ARM FIQ dis. IRQ dis.)
R0 = 00173180, R1 = FFFFFF48, R2 = 00000000, R3 = D3D3E1AB
R4 = 00000000, R5 = 08000B60, R6 = 00000000, R7 = 0800013F
USR: R8 =52894D31, R9 =084C44C1, R10=8D206C51, R11 =58311700, R12
=AC0C7CD7
R13=08000BA0, R14=08000137
FIQ: R8 =180A8884, R9 =00200200, R10=97D50C37, R11 =081E1C10, R12
=18A40002
R13=00008000, R14=9167F273, SPSR=2E0008E8
SVC: R13=04A9A810, R14=00000040, SPSR=2E0018E8
ABT: R13=2E6FA985, R14=3C000004, SPSR=00000393
IRQ: R13=2067F940, R14=0D044C2C, SPSR=2E0018E9
UND: R13=01004080, R14=00000008, SPSR=0000039B