https://sourceware.org/bugzilla/show_bug.cgi?id=31115
--- Comment #5 from Nick Clifton <nickc at redhat dot com> ---
(In reply to Thiago Jung Bauermann from comment #4)
Hi Thiago,
> $ gcc -g -o pr25124 ~/src/binutils-gdb/gdb/testsuite/gdb.arch/pr25124.S
> $ gdb pr25124
> Reading symbols from pr25124...
> (gdb) x/i main
> 0x103e5 <main>: bx pc
> (gdb) x/i main+8
> 0x103ed <main+7>: vrhadd.u16 d14, d14, d31
> (gdb) quit
>
> Interestingly, as can be seen above "x/i main" actually works fine.
Except that the address is displayed with the bottom bit set, which
might be confusing the readers. Maybe.
> it's "x/i main+8" that breaks. This is a detail that I just noticed.
>
> There's another thing I just discovered : I can reproduce GDB's bad
> behavior on an ELF executable (produced by GCC from the .S file), but
> not on a .o file produced directly by gas:
Or one that is produced by using gcc to invoke just gas. ie compiling with
"-c".
> $ as -g -o pr25124.o ~/src/binutils-gdb/gdb/testsuite/gdb.arch/pr25124.S
> $ gdb pr25124.o
> Reading symbols from pr25124.o...
> (gdb) x/i main
> 0x0 <main>: bx pc
> (gdb) x/i main+8
> 0x8 <main+8>: bx lr
> (gdb) quit
Interestingly my patch makes things even worse for the fully linked executable:
$ gdb pr25124.with-nicks-patch
GNU gdb (GDB) Fedora Linux 13.2-6.fc38
[...]
(gdb) x/i main
0x8243 <_start+158>: movs r0, r0
(gdb) x/i main+8
0x824b <main+7>: b.n 0x898e
So please consider it withdrawn.
> Both the executable and the .o file have the LSB bit set in main's
> DW_AT_low_pc:
> So for some reason GDB is fine with an object file containing the wrong
> DW_AT_low_pc in main's DIE, but not when it's with a "full blown"
> executable.
My guess - totally unproven - is that GDB has special code to mask thumb
addresses for object files, but for some reason this code is not applied
to linked executables.
I do wonder if this is something that GDB has already partially fixed, and
maybe this fix needs to be extended...
Anyway I am investigating gas some more...
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