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Subject: [PATCH v12 0/11 Add support for CRC64 generation in linker
Date: Mon,  6 Mar 2023 14:31:47 +0100
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Patchset XII
testsuite fixed to skip some tests.

Too limited flash space
* tic4x-coff, tic54x-cof
No support for the ".section" directive
(Neither are flash based micros and unlikely to use the feature)
* ns32k-pc532-macho
* pdp11-dec-aout
* powerpc-ibm-aix5.2.0
* rs6000-aix4.3.3
* alpha-linuxecoff

Patchset XI
During final generation of CRC, the output sections will be searched
for the section that contains the address of the digest
and this will be the selected section.

The 'DIGEST SECTION "name"' command is removed.

Added multiple test for error conditions when testing DIGEST

Patchset 10
Forget patchset IX.
Managed to push the master branch.
This is the real thing.

Patchset IX
Endian:
Default small endian.
Override with switches: -BE, -LE
Override in label using [#BE] and [#LE]

  DIGEST "<label>[#BE|#LE]" "CRC32"              (start, end)
  DIGEST "<label>[#BE|#LE]" "CRC64-ECMA"         (start, end)
  DIGEST "<label>[#BE|#LE]" "CRC64-GO-ISO"       (start, end)
  DIGEST "<label>[#BE|#LE]" "CRC64-GO-ISO-R"     (start, end)
  DIGEST "<label>[#BE|#LE]" "CRC64-WE"           (start, end)
  DIGEST "<label>[#BE|#LE]" "CRC64-XZ"           (start, end)
  DIGEST "<label>[#BE|#LE]"  POLY (<params>)     (start, end)
  DIGEST TABLE "<label>[#BE|#LE]"
  DIGEST SECTION "<section>"

Improve error messages. Some warnings are now errors.
Handle reported errors.
Keep DIGEST SECTION "name", but the whole feature should be deleted.

Patchset VIII
Memory in testsuite reduced to 16kB ROM and 4 kB RAM
All situated in the first 64 KB.

Patchset VII

Rebased against master
Fixed whitespace errors
Run indent on CRC files
Moved license to ld directory and renamed to COPYING.<website>
Added comments to COPYING.www.sunshine2k.de explaining what it is.

Patchset six
Commands changes so you always get little endian
but can override this in the linker command file.

  DIGEST "<label>[.BE]" "CRC32"              (start, end)
  DIGEST "<label>[.BE]" "CRC64-ECMA"         (start, end)
  DIGEST "<label>[.BE]" "CRC64-GO-ISO"       (start, end)
  DIGEST "<label>[.BE]" "CRC64-GO-ISO-R"     (start, end)
  DIGEST "<label>[.BE]" "CRC64-WE"           (start, end)
  DIGEST "<label>[.BE]" "CRC64-XZ"           (start, end)
  DIGEST "<label>[.BE]"  POLY (<params>)     (start, end)
  DIGEST TABLE "<label>[.BE]"
  DIGEST SECTION "<section>"

Each command has a label, which gets defined (not include ".BE")

It has been built natively as well as with the following setup
to configure.

  --target=x86_64-pc-linux-gnu
  --target=x86_64-w64-mingw32
  --target=aarch64-linux-gnu
  --target=powerpc64-linux-gnu
  --target=mips-elf
  --enable-targets=all --enable-64-bit-bfd 

A testsuite for all predefined algorithms are added.
The testsuite calculates the CRC for the "123456789"
string which is common.
The expected checksum value is provided.
The check ensures that a table is generated, but does not
check the binary contents of the table.
It is indirectly checked by using the same table for the
algorithm

The "DIGEST POLY" commands are checked by using
the the "CRC32" and "CRC64-ECMA" polynomes and parameters.

There is an online calculator at
http://www.sunshine2k.de/coding/javascript/crc/crc_js.html

There are no testsuites for the DEBUG ON|OFF, TIMESTAMP and
"DIGEST SECTION" commands yet.

The testsuite will fail if "DEBUG ON" is executed due to
verbose output.

The TIMESTAMP output varies with time and is difficult to test.

The DIGEST SECTION command is not tested, because this
need a little extra discussion.
I have not seen any other suitable sections being generated.

Since the information at http://www.sunshine2k.de/ has
been very useful, their license (MIT) is added.

Code examples for the CRC check routines that needs to be in the
user source is added to the documentation with copyright statements.
Should they be there, or is it enough to have the license
in the source code?

The Makefile.in is manually generated since I had a HDD crash
and upgraded to a new disk and installed Ubuntu 22.04.
The autotools are upgraded to 2.71. The build system
did not like this, so I installed 2.69.
This changes a lot more than the autotools-2.69 in Ubuntu 18.04
so I resorted to manual edit of Makefile.in.

Maybe someone should run autotools and generate this automatically
instead of applying the the manual edit.

Added instructions to build ldint.pdf which is not buildable today.

The system has only been tested on a PC == little endian.
I do not have a big endian host, but maybe someone could
test it on such a host.

The way endianess is implemented, it is easy for the user
to supply a workaround by specifying another endianess.



Fifth patchset.

+* The linker script has a new command to insert a timestamp
+  TIMESTAMP
+  inserts the current time (seconds since Epoch) as a 64-bit value
+
+* The linker script syntax has new commands for debugging a linker script
+  DEBUG ON  turns on debugging
+  DEBUG OFF turns off debugging
+
+* The linker script syntax has new commands for handling CRC-32/64 calculations
+  on the '.text' section
+  It uses code from https://www.libcrc.org/
+
+  DIGEST "CRC32"              (start, end)
+  DIGEST "CRC64-ECMA"         (start, end)
+  DIGEST "CRC64-ISO"          (start, end)
+  DIGEST "CRC64-WE"           (start, end)
+  DIGEST POLY (size, polynome)(start, end)
+  DIGEST POLYI(size, polynome)(start, end) (inversion during CRC calculation)
+  DIGEST TABLE
+  DIGEST SECTION "<section>

ran indent on the new files.

The *.d files in the testsuite was edited to 
reduce size and to remove all '(' characters.
The new linker can link using the testsuite/ld-script/*.t
linker files, but they do not pass the 'make check-ld'
test.

Fourth patchset.
Get rid of binaries in testsuite.

Here is the third patchset for introducing CRC64 generation.
This has focused on supporting maintainability of the feature.
In order to do so, CRC32 generation has been introduced to
detect issues when extending the linker with another algoritm
for checking integrity of the image.
This will simplify adding other algorithms like SHA algoritms
in the future.

In addition, the TIMESTAMP command is used to store the current time
in seconds since Epoch is stored in the image.

The main routine for calculating CRCs has been broken down
in subroutines which allow other algorithms.

An algorithm typically needs
<type> *init_<algo>_tab( <type> poly )
<type> calc_<algo>_inv( const unsigned char *input_str, size_t num_bytes );
<type> calc_<algo>    ( const unsigned char *input_str, size_t num_bytes );
void lang_add_<algo>_syndrome(bool invert, bfd_vma poly)
void lang_add_<algo>_table(void)

The common functions are:
* bool get_text_section_contents(void)
  This reads the '.text' section and its contents
  Pointers are stored in the global variables
  asection *text_section
  char     *text_contents
* bool set_crc_checksum(bfd_vma crc, bfd_vma addr, bfd_vma size)
  Stores the CRC at the index addr. The size of the CRC in bytes is specified.
  Storing something larger that 64-bit is not supported here.
* bool symbol_lookup(char *name, bfd_vma *val)
  Gets the value of a symbol into 'val'. Returns false if not found.

To add CRC32 support means adding the following commands
* CRC32 CRC32                    '(' crc_start ',' crc_end ')'
* CRC32 POLY  '[' mustbe_exp ']' '(' crc_start ',' crc_end ')'
* CRC32 POLYI '[' mustbe_exp ']' '(' crc_start ',' crc_end ')'

================
Here is the second patchset for introducing CRC64 generation in the linker
This is mainly looking at indentation and whitespace errors.
The patches applies cleanly without whitespace error
except for the last patch which contains the testsuite.
When the contents of .text is printed out, sometimes
the last byte of a line in the CRC table is a space.
This is reported as a whitespace error.

Supports the following new linker commands:
* CRC64 ECMA                     '(' crc_start ',' crc_end ')'
* CRC64 ISO                      '(' crc_start ',' crc_end ')'
* CRC64 POLY  '[' mustbe_exp ']' '(' crc_start ',' crc_end ')'
* CRC64 POLYI '[' mustbe_exp ']' '(' crc_start ',' crc_end ')'
* CRC64 TABLE

ECMA  == 0x42F0E1EBA9EA3693
ISO   == 0xD800000000000000
POLY  == Allows your own polynome
POLYI == Allows your own polynome, with inversion during calc

The CRC is calculated from crc_start to crc_end (not included)

The "CRC64 <polynome> command
* Allows specifying the polynom (ECMA(default), ISO or your own)
* Allows for inversion in the CRC calculation (CRC64-WE)
* Allows specifying the area that should be checked.
* reserves room for the CRC (8 bytes)
* Declares a symbol ___CRC64___ for the address of the CRC.
* Declares a symbol ___CRC64_START___ for the first address of the checked area
* Declares a symbol ___CRC64_END___ for the first address after the checked area

The symbols names are declared in "checksum.h".
If the names are unsuitable, it is easy to change.

The CRC TABLE command
  This is used to speed up the CRC calculation.
* Creates a 2kB table which speeds up the CRC calculation
* Can insert the 2kB table into the .text section at current location.
* Declares a symbol ___CRC64_TABLE___ if the table is inserted.

Comments on the code:

The process of calculation involves:
* Check if CRC is requested
* Validation of CRC prerequisites
* get .text section
* get .text section contents
* calculate CRC over the area
* insert the CRC in the correct location
====================================

This version also supports the
* DEBUG ON
* DEBUG OFF
turning on/off yydebug
I find it useful for debugging the build, but it can easly be removed.

This patch contains a lot of debug output, that is enabled by
#define DEBUG_CRC 1
This should be removed in the final version.

The ld.texi stuff needs some more work. Not very experienced with that.

Added an entry in NEWS

Added 4 test cases for the different CRC64 polynome commands.
All testcases generate a CRC table.

The code is using the libcrc released under an MIT license found in
* https://www.libcrc.org/
* https://github.com/lammertb/libcrc/tree/v2.0
Author:  Lammert Bies
A license for libcrc is added to the patch.

[PATCH v12 01/11] DIGEST: LICENSING
[PATCH v12 02/11] DIGEST: NEWS
[PATCH v12 03/11] DIGEST: Documentation
[PATCH v12 04/11] DIGEST: testsuite
[PATCH v12 05/11] DIGEST: ldlex.l
[PATCH v12 06/11] DIGEST: ldgram.y
[PATCH v12 07/11] DIGEST: ldmain.c
[PATCH v12 08/11] DIGEST: ldlang.*: add timestamp
[PATCH v12 09/11] DIGEST: calculation
[PATCH v12 10/11] DIGEST: Makefile.*
[PATCH v12 11/11] Build ldint