[RISCV] Add thread-pointer relaxations for local-exec TLS model#1534
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Jonathon Penix (jonathonpenix) wants to merge 3 commits into
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[RISCV] Add thread-pointer relaxations for local-exec TLS model#1534Jonathon Penix (jonathonpenix) wants to merge 3 commits into
Jonathon Penix (jonathonpenix) wants to merge 3 commits into
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Implemented as defined in the psABI at [1] Broadly, local-exec TLS accesses may be relaxed from the full sequence (ex: lui/add/lw) to a single tp-relative instruction (ex: a tp-relative lw) if the offset is within +-2KB. We check for offset < 2048 as I don't think a negative tp offset is meaningful in "normal" operation. While here, I'm also removing the usage of applyTprelAdd--as far as I'm aware there are no other psABI-defined relaxations around this relocation, so this should be obsolete. A few misc. items to note: * This can misrelax the sequence if part is marked relaxable and part is not. I'm not sure there's a great way to prevent this that works in general and this is a) in line with some other RISC-V relaxations in eld and b) is consistent with what lld and bfd do. So I didn't worry about trying to handle this. * You can also see weird things happen if you write (probably erroneous) assembly with different addends. As far as I can tell, eld is relaxing such sequences consistently with lld/bfd, so I left it be. * I *think* it should be possible to change the tp-relative offset *after* the relaxation happens, causing a mislink. And I don't think we have any error checking that would catch these cases currently. This should be consistent with ex: the TLSDESC short-form relaxations, so I'm hoping to address this as a follow-up patch. [1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/e03d44ae2f0e1144f9498c2896b5ae25b0449398/riscv-elf.adoc?plain=1#L2531 Signed-off-by: Jonathon Penix <[email protected]>
Signed-off-by: Jonathon Penix <[email protected]>
Signed-off-by: Jonathon Penix <[email protected]>
Jonathon Penix (jonathonpenix)
marked this pull request as ready for review
July 20, 2026 23:43
Jonathon Penix (jonathonpenix)
requested a review
from Shankar Easwaran (quic-seaswara)
as a code owner
July 20, 2026 23:43
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Just linking this comment/request for changes from Shankar: #1428 (comment) Will come back to/update this accordingly |
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Implemented as defined in the psABI at [1]
Broadly, local-exec TLS accesses may be relaxed from the full sequence (ex: lui/add/lw) to a single tp-relative instruction (ex: a tp-relative lw) if the offset is within +-2KB. We check for offset < 2048 as I don't think a negative tp offset is meaningful in "normal" operation.
While here, I'm also removing the usage of applyTprelAdd--as far as I'm aware there are no other psABI-defined relaxations around this relocation, so this should be obsolete.
A few misc. items to note:
[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/e03d44ae2f0e1144f9498c2896b5ae25b0449398/riscv-elf.adoc?plain=1#L2531