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Differential D40624

csu: Implement _start using as to satisfy unwinders on i386
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Authored by dchagin on Jun 20 2023, 12:48 PM.
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rGd744a37a3ad4: csu: Implement _start using as to satisfy unwinders on i386
Summary

The right unwinding stop indicator should be CFI-undefined PC.
https://dwarfstd.org/doc/Dwarf3.pdf - page 118:
If a Return Address register is defined in the virtual unwind table,
and its rule is undefined (for example, by DW_CFA_undefined), then
there is no return address and no call address, and the virtual
unwind of stack activations is complete.

The hack localizing _start1 symbol removed.

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Event Timeline

dchagin created this revision.Jun 20 2023, 12:48 PM
Herald added a subscriber: imp. · View Herald TranscriptJun 20 2023, 12:48 PM
dchagin requested review of this revision.Jun 20 2023, 12:48 PM
Harbormaster completed remote builds in B52160: Diff 123490.Jun 20 2023, 12:48 PM
dchagin edited the summary of this revision. (Show Details)Jun 20 2023, 12:52 PM
dchagin added a reviewer: kib.
dchagin abandoned this revision.Jun 26 2023, 12:18 PM

https://reviews.freebsd.org/D40623

dchagin reclaimed this revision.Jun 30 2023, 7:50 AM

I suggest don't waste time with rewriting _start1 on i386

kib added a comment.Jun 30 2023, 12:42 PM
In D40624#928890, @dchagin wrote:

I suggest don't waste time with rewriting _start1 on i386

What do you mean? i386 userspace, unlike kernel, is there with us for long time.

dchagin added a comment.Jun 30 2023, 2:03 PM
In D40624#928940, @kib wrote:
In D40624#928890, @dchagin wrote:

I suggest don't waste time with rewriting _start1 on i386

What do you mean? i386 userspace, unlike kernel, is there with us for long time.

Sure, I want to finish our arm64 and libunwind before 14.0 is out to release a libunwind too, and after that I want to finish i386,
but I'm not sure I have enough time for i386 due to arm64 has much more unresolved issues

btw, with latest changes libunwind x86_64 make check is green, thank you

dchagin updated this revision to Diff 124372.Jul 9 2023, 12:14 PM
dchagin edited the summary of this revision. (Show Details)

Implement _start using as

Harbormaster completed remote builds in B52518: Diff 124372.Jul 9 2023, 12:14 PM
dchagin updated this revision to Diff 124382.Jul 9 2023, 4:46 PM

cfi_offsett for %ebp set to -4, ie to 0

Harbormaster completed remote builds in B52523: Diff 124382.Jul 9 2023, 4:46 PM
kib added inline comments.Jul 9 2023, 11:28 PM
lib/csu/Makefile.inc
47

The main reason why I mostly agree with the change, is due to removal of the hack for _start1.

lib/csu/i386/crt1_s.S
81

This comment should go into the #else block.

dchagin updated this revision to Diff 124425.Jul 10 2023, 8:59 AM

csu: Implement _start using as to satisfy unwinders on i386

The right unwinding stop indicator should be CFI-undefined PC.
https://dwarfstd.org/doc/Dwarf3.pdf - page 118:
If a Return Address register is defined in the virtual unwind table,
and its rule is undefined (for example, by DW_CFA_undefined), then
there is no return address and no call address, and the virtual
unwind of stack activations is complete.

The hack localizing _start1 symbol removed.

Harbormaster completed remote builds in B52534: Diff 124425.Jul 10 2023, 8:59 AM
kib accepted this revision.Jul 10 2023, 10:15 AM

I suppose the latest comment is really a commit message.

lib/csu/i386/crt1_s.S
57

why not use the local 1: label and then calll 1f?

This revision is now accepted and ready to land.Jul 10 2023, 10:15 AM
dchagin updated this revision to Diff 124426.Jul 10 2023, 11:13 AM

.L was used due to it not entered into the symbol table, replaced by numbered labels.

This revision now requires review to proceed.Jul 10 2023, 11:13 AM
Harbormaster completed remote builds in B52535: Diff 124426.Jul 10 2023, 11:13 AM
dchagin retitled this revision from csu: Add stop indicator to _start to satisfy unwinders on i386 to csu: Implement _start using as to satisfy unwinders on i386.Jul 10 2023, 11:14 AM
dchagin edited the summary of this revision. (Show Details)
dchagin marked 2 inline comments as done.
kib accepted this revision.Jul 10 2023, 11:42 AM
This revision is now accepted and ready to land.Jul 10 2023, 11:42 AM
Closed by commit rGd744a37a3ad4: csu: Implement _start using as to satisfy unwinders on i386 (authored by dchagin). · Explain WhyJul 11 2023, 12:12 PM
This revision was automatically updated to reflect the committed changes.
dchagin added a commit: rGd744a37a3ad4: csu: Implement _start using as to satisfy unwinders on i386.

Revision Contents
Changeset List

PathSize
lib/
csu/
6 lines
i386/
3 lines
21 lines
58 lines

Diff 124489

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lib/csu/Makefile.inc

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lib/csu/i386/Makefile

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lib/csu/i386/crt1_c.c

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lib/csu/i386/crt1_s.S

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