[Bug rust/31082] New: rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[Bug rust/31082] New: rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

            Bug ID: 31082
           Summary: rust-parse infers `0xffffffd00000009a` and other
                    addresses as i128, preventing `as *mut _` coercions in
                    `print`
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rust
          Assignee: unassigned at sourceware dot org
          Reporter: tpzker at thepuzzlemaker dot info
  Target Milestone: ---

Created attachment 15226
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15226&action=edit
[PATCH] rust-parse: Infer some integer constants as u64

I've been working on an operating system in Rust for learning purposes, and
have found myself having to deal with addresses greater than `2^63-1` due to
canonicalization and higher-half kernels. Due to a bug (#29735) in GDB 13.2,
fixed in GDB 14 HEAD, however, I have been using the GDB 14 branch to perform
debugging.

However, when trying to print expressions as such:
```
p (0xffffffd00000009a as *mut u64)
```
The system returns an error: `That operation is not available on integers of
more than 8 bytes.`

To reproduce this, compile a simple Rust program like such (in `tmp.rs`, for
example):
```rs
fn main() { println!("hello world!") }
```
Then `b tmp::main` and run the print command above.

After some debugging, I've discovered that this stems from the following patch:
https://sourceware.org/pipermail/gdb-patches/2023-March/198410.html

This patch added support for `i128`, however in this process, made all `u64`s
`(2 ** 63) - 1 <= x <= (2 ** 64) - 1` inferred to be i128s, when they really
should be `u64`s. This causes the `as *mut u64` operation to fail.

This only occurs for addresses in the higher half, and not any other
addresses--perhaps why it was not discovered earlier.

I have attached a patch that is a bit hacky, but does solve this issue. It will
regress some inference of large values as i128, however, and that will require
explicit suffixing as `[number]i128`. I'm not sure how to better solve that,
though.

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[Bug rust/31082] rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[tpzker at thepuzzlemaker dot info]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

The Puzzlemaker <tpzker at thepuzzlemaker dot info> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tpzker at thepuzzlemaker dot info

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[Bug rust/31082] rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-11-24
                 CC|                            |tromey at sourceware dot org
     Ever confirmed|0                           |1

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
FWIW you can reproduce it without a program at all, just "set lang rust".

I tend to think value_cast can be fixed instead.  This bug probably
affects any language that can create a 128-bit integer.

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[Bug rust/31082] rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

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[Bug rust/31082] rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
https://sourceware.org/pipermail/gdb-patches/2023-November/204503.html

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[Bug rust/31082] rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

--- Comment #3 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=44671f3f7f4c6435e7a639ad2215629f4e1ea8a7

commit 44671f3f7f4c6435e7a639ad2215629f4e1ea8a7
Author: Tom Tromey <tom@tromey.com>
Date:   Fri Nov 24 12:10:53 2023 -0700

    Allow cast of 128-bit integer to pointer

    PR rust/31082 points out that casting a 128-bit integer to a pointer
    will fail.  This happens because a case in value_cast was not
    converted to use GMP.

    This patch fixes the problem.  I am not really sure that testing
    against the negative value here makes sense, but I opted to just
    preserve the existing behavior rather than change it.

    Regression tested on x86-64 Fedora 38.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31082

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[Bug rust/31082] rust-parse infers `0xffffffd00000009a` and other addresses as i128, preventing `as *mut _` coercions in `print`

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31082

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |15.1

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
Fixed.

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