[Bug ld/30193] New: ASCII command length checking corner cases not properly handled

[pexu at sourceware dot mail.kapsi.fi]

https://sourceware.org/bugzilla/show_bug.cgi?id=30193

            Bug ID: 30193
           Summary: ASCII command length checking corner cases not
                    properly handled
           Product: binutils
           Version: 2.41 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: pexu at sourceware dot mail.kapsi.fi
  Target Milestone: ---

Created attachment 14727
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14727&action=edit
Handle ASCII corner cases, adjust test case accordingly

Hi.

ASCII (expr) "string" length checking is currently off by one and zero length
is handled in a manner that might be unexpected.

ld/ldlang.c: (excerpt, in-between lines omitted)
8464   if (size == 0)
8466     size = len + 1;
8467   else if (len >= size)
8468     {
8469       len = size - 1;
8473     }

`size' is the output size (zero for ASCIZ), and `len' is the actual length of
the input string (that has been processed).  As the checking currently uses
`len >= size' it is not possible to output a string that is exactly the
allocated size, e.g. `ASCII (5) "ascii"'.

Also, as lang_add_string() processes both ASCIZ and ASCII commands it is not
possible to produce an empty output, e.g. `ASCII (0) ""'.  This might be useful
if the command would be used to produce variable padding.

Attaching a proposed patch that solves both of these issues.  Instead of
relying on `size == 0' a simple boolean is added (think this as optional<
size_t >).  Also, updated the test case to handle these corner cases, including
one that leads to input string truncation.  (Also, now there are no trailing
whitespaces in the expected result.)

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