Re: [Valgrind-users] Unhandled instruction bytes (C++, x86 on amd64)

[John R. <jr...@bi...>]

On 03/16/2018 1439 UTC, Zack Weinberg wrote:
> On Fri, Mar 16, 2018 at 1323 UTC, John Reiser wrote:
>>
>> The code 0x67 0xE8 0x7D 0xFF is "addr32 callq ...".  Valgrind is complaining
>> about the 'addr32' opcode prefix.  The compiler for locale_init.cc did a
>> not-so-good job.  The addr32 prefix is a total waste; remove it.
> 
> This _could_ be an alignment hack.  I don't see any of these prefixes
> in my copy of libstdc++ but the compiler could plausibly be trying to
> make the instruction right after the call be on a tidy address
> boundary.

The 0x67 was at 0x48cc63d which is (-3 mod 16), so the following instruction
is at (+3 mod 16) [1 for the 0x67, 1 for the 0xE8, 4 for the 32-bit displacement].
Alignment was not close to any auspicious boundary.