https://sourceware.org/bugzilla/show_bug.cgi?id=34844
Bug ID: 34844
Summary: GNU ld RISC-V R_RISCV_ALIGN addend with the top bit
set never terminates
Product: binutils
Version: 2.46
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: basavesh.shivakumar at wsu dot edu
Target Milestone: ---
Created attachment 17164
--> https://sourceware.org/bugzilla/attachment.cgi?id=17164&action=edit
repro
I'm reporting this bug on behalf of my team: Ananta Srikar Puranam, Emily West,
Dr. Swarn Priya, Dr. Peng Gao and Dr. Basavesh Ammanaghatta Shivakumar.
Summary
=======
A valid RISC-V relocatable object whose R_RISCV_ALIGN relocation carries an
addend with its top bit set (e.g. -1, 0x8000000000000000 on RV64, or 0x80000000
sign-extended on RV32) makes _bfd_riscv_relax_align loop forever: alignment
doubles to 2^63, stays <= the unsigned addend, then wraps to 0 and never
exceeds it (bfd/elfnn-riscv.c:5253 released 2.46, :5555 current 85f5ea68, :5562
instrumented build 3d45f46c, :5555 master 17d606a601f4). The mandatory ALIGN
pass runs even with --no-relax, so static, PIE and shared links all hang; only
-r links are skipped. Released GNU ld 2.46, the Ubuntu riscv64-linux-gnu-ld
2.46, current 2.47.50.20261016 plain, and both sanitizer builds time out while
the addend-6 controls link; no sanitizer memory diagnostic is produced because
the loop variable is unsigned.
Reproduction
============
1. Download and extract
`bfd-riscv-align-negative-addend-nonterminating-relaxation-reproducer.tar.gz`.
2. Run the following command with an ld.bfd or all-target `ld-new` binary that
supports the emulation used by the reproducer:
LD=/path/to/ld-new sh repro.sh
The archive contains the fixed input files, independent controls, helper
scripts needed by `repro.sh`, and their checksums. The script uses a temporary
directory and does not modify the source tree.
Observed result
===============
A valid RISC-V relocatable object whose R_RISCV_ALIGN relocation carries an
addend with its top bit set (e.g. -1, 0x8000000000000000 on RV64, or 0x80000000
sign-extended on RV32) makes _bfd_riscv_relax_align loop forever: alignment
doubles to 2^63, stays <= the unsigned addend, then wraps to 0 and never
exceeds it (bfd/elfnn-riscv.c:5253 released 2.46, :5555 current 85f5ea68, :5562
instrumented build 3d45f46c, :5555 master 17d606a601f4). The mandatory ALIGN
pass runs even with --no-relax, so static, PIE and shared links all hang; only
-r links are skipped. Released GNU ld 2.46, the Ubuntu riscv64-linux-gnu-ld
2.46, current 2.47.50.20261016 plain, and both sanitizer builds time out while
the addend-6 controls link; no sanitizer memory diagnostic is produced because
the loop variable is unsigned.
Expected result
===============
GNU ld should either produce the correct output or reject the input with a
normal diagnostic. It should not crash, hang, execute undefined behavior, read
outside an input-derived allocation, or produce the described malformed
output.
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