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Port pdumper to m68k

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Problem reported by John Paul Adrian Glaubitz (bug#44531).
* src/pdumper.c (DUMP_RELOCATION_ALIGNMENT_BITS): Remove.  It’s
not needed for optimization, as today’s compilers deduce that
multiplying and dividing by the alignment can be done with shifts.
All uses changed to use DUMP_RELOCATION_ALIGNMENT.
(DUMP_RELOCATION_ALIGNMENT) [__mc68000__]:
Now min (4, alignof (Lisp_Object)), not 4.
(dump_reloc_set_offset): Change eassert to eassume to help
the compiler.
This commit is contained in:
Paul Eggert 2026-07-14 18:05:55 -07:00
parent 0818bb3eb3
commit 407de5142c
2 changed files with 19 additions and 6 deletions
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3
etc/NEWS
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@ -29,6 +29,9 @@ applies, and please also update docstrings as needed.
The traditional unexec dumper, deprecated since Emacs 27, has been
removed.
+++
*** The portable dumper now works on m68k a.out targets.
---
** Emacs's old 'ctags' program is no longer built or installed.
You are encouraged to use Universal Ctags <https://ctags.io/> instead.

22
src/pdumper.c
View file

@ -268,10 +268,20 @@ struct dump_table_locator
enum
{
DUMP_RELOC_TYPE_BITS = 5,
DUMP_RELOC_ALIGNMENT_BITS = 2,
/* Minimum alignment required by dump file format. */
DUMP_RELOCATION_ALIGNMENT = 1 << DUMP_RELOC_ALIGNMENT_BITS,
/* Minimum alignment required by dump file format. Although this can
be any integer power of 2 up to alignof (Lisp_Alignment),
larger values help dump_reloc_set_offset support larger offsets.
The fix for bug#44531 was discovered late during Emacs 31 development,
so on Emacs 31 the value is 4 except on hosts where 4 is known to fail.
The only known failure is m68k a.out, so work around the problem
only if __mc68000__ is defined and the Lisp_Object alignment is 2,
which is a known property of the m68k a.out format. */
#ifdef __mc68000__
DUMP_RELOCATION_ALIGNMENT = min (4, alignof (Lisp_Object)),
#else
DUMP_RELOCATION_ALIGNMENT = 4,
#endif
/* The alignment granularity (in bytes) for objects we store in the
dump. Always suitable for heap objects; may be more aligned. */
@ -303,14 +313,14 @@ dump_reloc_set_type (struct dump_reloc *reloc, enum dump_reloc_type type)
static dump_off
dump_reloc_get_offset (struct dump_reloc reloc)
{
return reloc.raw_offset << DUMP_RELOC_ALIGNMENT_BITS;
return reloc.raw_offset * DUMP_RELOCATION_ALIGNMENT;
}
static void
dump_reloc_set_offset (struct dump_reloc *reloc, dump_off offset)
{
eassert (offset >= 0);
reloc->raw_offset = offset >> DUMP_RELOC_ALIGNMENT_BITS;
eassume (offset >= 0);
reloc->raw_offset = offset / DUMP_RELOCATION_ALIGNMENT;
if (dump_reloc_get_offset (*reloc) != offset)
error ("dump relocation out of range");
}