GNU bug report logs - #44173
28.0.50; gdb-mi mangles strings with octal escapes

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Mattias Engdegård <mattiase <at> acm.org>
Subject: bug#44173: closed (Re: bug#44173: 28.0.50; gdb-mi mangles strings
 with octal escapes)
Date: Fri, 06 Nov 2020 13:04:02 +0000

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Your bug report

#44173: 28.0.50; gdb-mi mangles strings with octal escapes

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 44173 <at> debbugs.gnu.org.

-- 
44173: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=44173
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Mattias Engdegård <mattiase <at> acm.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 44173-done <at> debbugs.gnu.org
Subject: Re: bug#44173: 28.0.50; gdb-mi mangles strings with octal escapes
Date: Fri, 6 Nov 2020 14:01:06 +0100

31 okt. 2020 kl. 14.57 skrev Mattias Engdegård <mattiase <at> acm.org>:

> The attached patch changes the default value of gdb-mi-decode-strings from nil to t.

This patch has now been pushed since it did not appear controversial. Changes are of course still possible.
With that, the bug is closed.

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From: Mattias Engdegård <mattiase <at> acm.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 28.0.50; gdb-mi mangles strings with octal escapes
Date: Fri, 23 Oct 2020 13:50:24 +0200

When GDB sends a string containing octally-escaped characters, it will be something like

 "abc\377def"

which is first massaged into JSON and then parsed as such, but since JSON doesn't recognise octal escapes, the result is

 "abc377def"

which is wrong. This assumes gdb-mi-decode-strings is nil, which it is by default; otherwise the octal escapes are decoded by a fragile preprocessing stage (gdb-mi-decode) which itself has known problems as noted in a comment.

Frankly, this business with going via JSON after several ad-hoc text-based transforms isn't very principled.

While the bug could be 'solved' by adding yet another regexp hack to gdb-mi-decode or gdb-mi-jsonify-buffer, I suggest we write a GDB/MI parser in Lisp directly, ditching the gdb-mi-decode preprocessing and JSON form entirely, solving this and related bugs once and for all. Many transforms can then be done on the S-expression result after parsing, which should be more efficient and less error-prone.

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