Re: [PATCH v5] Add negative repeat count to 'x' command

[Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>]

On 11/08/16 00:58, Pedro Alves wrote:
> On 08/08/2016 03:45 PM, Thomas Preudhomme wrote:
> > Sorry for the late reply but I noticed an issue in the tests added by
> > this patch for arm-none-eabi:
> >
> >
> > FAIL: gdb.base/examine-backward.exp: address zero boundary: examine 3
> > bytes forward from 0x0
> > NA->FAIL: gdb.base/examine-backward.exp char-width=1, print-max=20 take
> > 1 string backward (6/6)
> > NA->FAIL: gdb.base/examine-backward.exp char-width=1, print-max=20 take
> > 6 strings backward (pattern 1)
> >
> >
> > The first one is a testism:
> >
> > we match for: 0x\[0-9a-f\]+00.*:${byte}${byte}${byte}
> > but we get: 0x0:    0x7f    0x45    0x4c
> >
> > I'd thus suggest to match 0x\(\[0-9a-f\]+0\)?0 instead, with the right
> > amount of escaping (I don't know whether ? needs escaping and why + does
> > not need escaping in current pattern).
>
> We're examining at 0x0.  Shouldn't we expect literally "0x0"
> instead then?

That's what I would have done but I assumed that the test was passing on the 
machine it was developed and thus that some machine display 0x00000000 or something.

> > The other two seems like genuine errors. take 6 strings backward
> > (pattern 1) gives:
> >
> > gdb_expect_list pattern: /"ABCDEFGHIJKLMNOPQRST".../
> > x/-6s^M
> > 0x9aff <_fini+2>: "\277\370\274\b\274\236FpGABCDEFGHIJK"...^M
> > 0x9b13 <TestStrings+11>:        "LMNOPQRSTUVWXYZ"^M
> > 0x9b23 <TestStrings+27>:        ""^M
> > 0x9b24 <TestStrings+28>:        ""^M
> > 0x9b25 <TestStrings+29>:
> > "\343\201\273\343\201\222\343\201\273\343\201\222"^M
> > 0x9b32 <TestStrings+42>:        "01234567890123456789"...^M
> > (gdb) FAIL: gdb.base/examine-backward.exp: char-width=1, print-max=20:
> > take 6 strings backward (pattern 1)
> >
> >
> > take 1 string backward (6/6) gives:
> >
> > 0x9aff <_fini+2>: "\277\370\274\b\274\236FpGABCDEFGHIJK"...
> >
> >
> > Please let me know what I can do to help diagnose this error.
>
> The find-strings-backwards algorithm just looks back for '\0' to
> find string boundaries.  Looks like it just happens that in your
> case, the TestStrings array is immediately preceded by the
> tail of _fini, with no gap in between.
>
> Try this.  It's not strictly correct to assume that the linker
> places the objects consecutively, but it's probably safe
> in practice.

The patch works indeed. Thanks for your quick answer.

Best regards,

Thomas

> diff --git c/gdb/testsuite/gdb.base/examine-backward.c w/gdb/testsuite/gdb.base/examine-backward.c
> index b338503..187fad1 100644
> --- c/gdb/testsuite/gdb.base/examine-backward.c
> +++ w/gdb/testsuite/gdb.base/examine-backward.c
> @@ -32,6 +32,14 @@ literals.  The content of each array is the same as followings:
>    };
>  */
>
> +/* This is here just to ensure we have a null character before
> +   TestStrings, to avoid showing garbage when we look for strings
> +   backwards from TestStrings.  */
> +
> +const char NullString[] = {
> +  0x00
> +};
> +
>  const char TestStrings[] = {
>    0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
>    0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,