Re: [PATCH] Return lazy value from allocate_repeat_value

[Simon Marchi <simark@simark.ca>]

On 9/21/26 12:16 PM, Tom Tromey wrote:
> A user noticed that the "@" operator could cause a crash in gdb.  The
> bug here was that value::allocate_contents might limit the amount of
> memory allocated for the contents, but value_repeat did not respect
> this.
> 
> This patch fixes the problem by having allocate_repeat_value return a
> lazy value.  This defers to the memory reading to the "usual" code
> that does respect these limits.
> 
> Regression tested on x86-64 Fedora 43.
> 
> Note that the new test only reliably fails in an ASAN build.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34132
> ---
>  gdb/testsuite/gdb.base/printcmds.exp | 9 +++++++++
>  gdb/valops.c                         | 4 ----
>  gdb/value.c                          | 2 +-
>  3 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.base/printcmds.exp b/gdb/testsuite/gdb.base/printcmds.exp
> index 12933d898ed..0600eaf2ab6 100644
> --- a/gdb/testsuite/gdb.base/printcmds.exp
> +++ b/gdb/testsuite/gdb.base/printcmds.exp
> @@ -717,6 +717,15 @@ proc test_artificial_arrays {} {
>  	{p int1dim[0]@TWO@three}
>      gdb_test_escape_braces {p/x (short [])0x12345678} \
>  	" = ({0x1234, 0x5678}|{0x5678, 0x1234})"
> +
> +    # A regression test for a buffer overflow.  PR gdb/34132.
> +    gdb_test_no_output {set $ctable = (char *) ctable2}

Just wondering, is the use of the convenience var necessary?

> +    gdb_test_no_output "set max-value-size 16"
> +    gdb_test_no_output "set print elements 10"
> +    gdb_test {print $ctable[0] @ 20} \
> +	[quotemeta {$@DECIMAL = {97 'a', 88 'X' <repeats 15 times>...}}]
> +    gdb_test_no_output "set max-value-size 65536"
> +    gdb_test_no_output "set print elements 200"

Can you do

  with max-value-size 16 -- with print elements 10 -- ...

to avoid having to set and reset the settings?

Other than that, LGTM.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon