NetBSD Problem Report #59360

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Date: Sat, 26 Apr 2025 15:59:00 +0000 (UTC)
From: campbell+netbsd@mumble.net
Reply-To: campbell+netbsd@mumble.net
To: gnats-bugs@NetBSD.org
Subject: ld.elf_so(8): missing RELR support
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>Number:         59360
>Category:       bin
>Synopsis:       ld.elf_so(8): missing RELR support
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 26 16:00:00 +0000 2025
>Last-Modified:  Fri May 02 23:05:03 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The PackedBSD Relocation Elves, Inc.
>Environment:
>Description:
The RELR format is a compact format for R_*_RELATIVE-type relocations that dramatically reduces the size of relocation sections, which directly saves disk space and memory, and indirectly saves load time by reducing I/O and memory transactions.

No formal reference in the ELF gABI yet (https://www.sco.com/developers/gabi/latest/ch4.sheader.html) but here's a large dump of information about the background, motivation, and format:

https://maskray.me/blog/2021-10-31-relative-relocations-and-relr

GNU ld supports generating these sections on i386, amd64, amd64-with-ilp32, and powerpc64, with -Wl,-z,pack-relative-relocs.
>How-To-Repeat:
XXX add a simple test case that illustrates ld.elf_so's missing support for RELR
>Fix:
Yes, please!

>Audit-Trail:
From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src/sys/sys
Date: Sun, 27 Apr 2025 00:11:27 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sun Apr 27 00:11:27 UTC 2025

 Modified Files:
 	src/sys/sys: exec_elf.h

 Log Message:
 sys/exec_elf.h: Nix trailing whitespace.

 No functional change intended.

 Preparation for:

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.172 -r1.173 src/sys/sys/exec_elf.h

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src/sys/sys
Date: Sun, 27 Apr 2025 00:11:41 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sun Apr 27 00:11:40 UTC 2025

 Modified Files:
 	src/sys/sys: exec_elf.h

 Log Message:
 sys/exec_elf.h: Add some missing numbers from the ELF gABI.

 Fix the meta-number DT_ENCODING while here: it is defined to be 32,
 not 31; it is a name for the smallest DT_* tag that follows the rule
 of only even-numbered tags using d_ptr, and odd-numbered tags using
 either nothing or d_val.  Nothing uses DT_ENCODING directly, though,
 so this shouldn't affect anything.

 https://www.sco.com/developers/gabi/latest/ch5.dynamic.html

 Preparation for:

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.173 -r1.174 src/sys/sys/exec_elf.h

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src/tests/libexec/ld.elf_so
Date: Sun, 27 Apr 2025 00:11:57 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sun Apr 27 00:11:57 UTC 2025

 Modified Files:
 	src/tests/libexec/ld.elf_so: Makefile

 Log Message:
 tests/libexec/ld.elf_so/Makefile: Sort.

 Preparation for:

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.25 -r1.26 src/tests/libexec/ld.elf_so/Makefile

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src
Date: Fri, 2 May 2025 03:26:27 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri May  2 03:26:26 UTC 2025

 Modified Files:
 	src/distrib/sets/lists/debug: mi
 	src/distrib/sets/lists/tests: mi
 	src/tests/libexec/ld.elf_so: Makefile
 Added Files:
 	src/tests/libexec/ld.elf_so: h_r_rel.c t_r_rel.sh

 Log Message:
 ld.elf_so: Add a trivial test for R_*_RELATIVE relocations.

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.480 -r1.481 src/distrib/sets/lists/debug/mi
 cvs rdiff -u -r1.1373 -r1.1374 src/distrib/sets/lists/tests/mi
 cvs rdiff -u -r1.26 -r1.27 src/tests/libexec/ld.elf_so/Makefile
 cvs rdiff -u -r0 -r1.1 src/tests/libexec/ld.elf_so/h_r_rel.c \
     src/tests/libexec/ld.elf_so/t_r_rel.sh

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src
Date: Fri, 2 May 2025 22:30:29 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri May  2 22:30:29 UTC 2025

 Modified Files:
 	src/distrib/sets/lists/debug: mi
 	src/distrib/sets/lists/tests: mi
 	src/tests/lib/csu: Makefile t_hello.sh

 Log Message:
 lib/csu: Test a static PIE with RELR relocations.

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.482 -r1.483 src/distrib/sets/lists/debug/mi
 cvs rdiff -u -r1.1375 -r1.1376 src/distrib/sets/lists/tests/mi
 cvs rdiff -u -r1.9 -r1.10 src/tests/lib/csu/Makefile
 cvs rdiff -u -r1.1 -r1.2 src/tests/lib/csu/t_hello.sh

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src/sys/sys
Date: Fri, 2 May 2025 23:02:55 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri May  2 23:02:55 UTC 2025

 Modified Files:
 	src/sys/sys: exec_elf.h

 Log Message:
 sys/exec_elf.h: Add RELR definitions.

 The SHT_RELR .relr.dyn section, identified in DT_RELR dynamic tag,
 holds compressed R_*_RELATIVE-type relocations, substantially
 reducing the disk space occupied by many programs.

 Reference:

 Rahul Chaudhry, `Re: Proposal for a new section type SHT_RELR',
 generic-abi mailing list, 2018-02-07.

 https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/Jnz1lgLJAgAJ
 https://web.archive.org/web/20241213012330/https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/Jnz1lgLJAgAJ

 Proposed on tech-userlevel:
 https://mail-index.NetBSD.org/tech-userlevel/2025/04/27/msg014727.html

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.174 -r1.175 src/sys/sys/exec_elf.h

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src
Date: Fri, 2 May 2025 23:03:16 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri May  2 23:03:16 UTC 2025

 Modified Files:
 	src/libexec/ld.elf_so: headers.c reloc.c rtld.h
 	src/tests/libexec/ld.elf_so: t_r_rel.sh

 Log Message:
 ld.elf_so: Implement RELR relocations.

 The SHT_RELR-type .relr.dyn section, pointed to by the DT_RELR
 dynamic tag, holds compressed R_*_RELATIVE-type relocations,
 substantially reducing the disk space occupied by many programs.

 This commit adds support in ld.elf_so for relocating dynamically
 linked executables with RELR relocations.

 Reference:

 Rahul Chaudhry, `Re: Proposal for a new section type SHT_RELR',
 generic-abi mailing list, 2018-02-07.

 https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/Jnz1lgLJAgAJ
 https://web.archive.org/web/20241213012330/https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/Jnz1lgLJAgAJ

 Proposed on tech-userlevel:
 https://mail-index.NetBSD.org/tech-userlevel/2025/04/27/msg014727.html

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.74 -r1.75 src/libexec/ld.elf_so/headers.c
 cvs rdiff -u -r1.119 -r1.120 src/libexec/ld.elf_so/reloc.c
 cvs rdiff -u -r1.148 -r1.149 src/libexec/ld.elf_so/rtld.h
 cvs rdiff -u -r1.1 -r1.2 src/tests/libexec/ld.elf_so/t_r_rel.sh

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: "Taylor R Campbell" <riastradh@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/59360 CVS commit: src
Date: Fri, 2 May 2025 23:04:06 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri May  2 23:04:06 UTC 2025

 Modified Files:
 	src/lib/csu/common: crt0-common.c
 	src/tests/lib/csu: t_hello.sh

 Log Message:
 lib/csu: Add support for RELR relocations in static PIEs.

 Same logic as in ld.elf_so, but baked into the executable itself for
 static PIEs.

 Addendum to proposal on tech-userlevel:
 https://mail-index.NetBSD.org/tech-userlevel/2025/04/27/msg014727.html

 PR bin/59360: ld.elf_so(8): missing RELR support


 To generate a diff of this commit:
 cvs rdiff -u -r1.29 -r1.30 src/lib/csu/common/crt0-common.c
 cvs rdiff -u -r1.2 -r1.3 src/tests/lib/csu/t_hello.sh

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

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